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* [PATCH] drivers: char: hvc: add arm JTAG DCC console support
@ 2010-11-30 19:25 Daniel Walker
  2010-11-30 19:57 ` Nicolas Pitre
                   ` (2 more replies)
  0 siblings, 3 replies; 39+ messages in thread
From: Daniel Walker @ 2010-11-30 19:25 UTC (permalink / raw)
  To: linux-kernel
  Cc: linux-arm-msm, Daniel Walker, Tony Lindgren, Arnd Bergmann,
	Nicolas Pitre, Greg Kroah-Hartman, Mike Frysinger, Andrew Morton,
	Alan Cox, Randy Dunlap, FUJITA Tomonori, linuxppc-dev

This driver adds a basic console that uses the arm JTAG
DCC to transfer data back and forth. It has support for
ARMv6 and ARMv7.

This console is created under the HVC driver, and should be named
/dev/hvcX (or /dev/hvc0 for example).

Cc: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Nicolas Pitre <nico@fluxnic.net>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Daniel Walker <dwalker@codeaurora.org>
---
 drivers/char/Kconfig   |    9 +++
 drivers/char/Makefile  |    1 +
 drivers/char/hvc_dcc.c |  133 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 143 insertions(+), 0 deletions(-)
 create mode 100644 drivers/char/hvc_dcc.c

diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 43d3395..d4a7776 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -682,6 +682,15 @@ config HVC_UDBG
        select HVC_DRIVER
        default n
 
+config HVC_DCC
+       bool "ARM JTAG DCC console"
+       depends on ARM
+       select HVC_DRIVER
+       help
+         This console uses the JTAG DCC on ARM to create a console under the HVC
+	 driver. This console is used through a JTAG only on ARM. If you don't have
+	 a JTAG then you probably don't want this option.
+
 config VIRTIO_CONSOLE
 	tristate "Virtio console"
 	depends on VIRTIO
diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index ba53ec9..fa0b824 100644
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -34,6 +34,7 @@ obj-$(CONFIG_HVC_CONSOLE)	+= hvc_vio.o hvsi.o
 obj-$(CONFIG_HVC_ISERIES)	+= hvc_iseries.o
 obj-$(CONFIG_HVC_RTAS)		+= hvc_rtas.o
 obj-$(CONFIG_HVC_TILE)		+= hvc_tile.o
+obj-$(CONFIG_HVC_DCC)		+= hvc_dcc.o
 obj-$(CONFIG_HVC_BEAT)		+= hvc_beat.o
 obj-$(CONFIG_HVC_DRIVER)	+= hvc_console.o
 obj-$(CONFIG_HVC_IRQ)		+= hvc_irq.o
diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
new file mode 100644
index 0000000..6470f63
--- /dev/null
+++ b/drivers/char/hvc_dcc.c
@@ -0,0 +1,133 @@
+/* Copyright (c) 2010, Code Aurora Forum. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#include <linux/console.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/moduleparam.h>
+#include <linux/types.h>
+
+#include <asm/processor.h>
+
+#include "hvc_console.h"
+
+/* DCC Status Bits */
+#define DCC_STATUS_RX		(1 << 30)
+#define DCC_STATUS_TX		(1 << 29)
+
+static inline u32 __dcc_getstatus(void)
+{
+	u32 __ret;
+
+	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
+		: "=r" (__ret) : : "cc");
+
+	return __ret;
+}
+
+
+#if defined(CONFIG_CPU_V7)
+static inline char __dcc_getchar(void)
+{
+	char __c;
+
+	asm("get_wait:	mrc p14, 0, pc, c0, c1, 0                          \n\
+			bne get_wait                                       \n\
+			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
+		: "=r" (__c) : : "cc");
+
+	return __c;
+}
+#else
+static inline char __dcc_getchar(void)
+{
+	char __c;
+
+	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
+		: "=r" (__c));
+
+	return __c;
+}
+#endif
+
+#if defined(CONFIG_CPU_V7)
+static inline void __dcc_putchar(char c)
+{
+	asm("put_wait:	mrc p14, 0, pc, c0, c1, 0                 \n\
+			bcs put_wait                              \n\
+			mcr p14, 0, %0, c0, c5, 0                   "
+	: : "r" (c) : "cc");
+}
+#else
+static inline void __dcc_putchar(char c)
+{
+	asm("mcr p14, 0, %0, c0, c5, 0	@ write a char"
+		: /* no output register */
+		: "r" (c));
+}
+#endif
+
+static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
+{
+	int i;
+
+	for (i = 0; i < count; i++) {
+		while (__dcc_getstatus() & DCC_STATUS_TX)
+			cpu_relax();
+
+		__dcc_putchar((char)(buf[i] & 0xFF));
+	}
+
+	return count;
+}
+
+static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
+{
+	int i;
+
+	for (i = 0; i < count; ++i) {
+		int c = -1;
+
+		if (__dcc_getstatus() & DCC_STATUS_RX)
+			c = __dcc_getchar();
+		if (c < 0)
+			break;
+		buf[i] = c;
+	}
+
+	return i;
+}
+
+static const struct hv_ops hvc_dcc_get_put_ops = {
+	.get_chars = hvc_dcc_get_chars,
+	.put_chars = hvc_dcc_put_chars,
+};
+
+static int __init hvc_dcc_console_init(void)
+{
+	hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
+	return 0;
+}
+console_initcall(hvc_dcc_console_init);
+
+static int __init hvc_dcc_init(void)
+{
+	hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
+	return 0;
+}
+device_initcall(hvc_dcc_init);
-- 
1.7.1

-- 
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-11-30 19:25 [PATCH] drivers: char: hvc: add arm JTAG DCC console support Daniel Walker
@ 2010-11-30 19:57 ` Nicolas Pitre
  2010-11-30 21:17   ` Arnd Bergmann
  2010-12-01  5:30 ` Stephen Boyd
  2011-04-07 18:39 ` RONETIX - Asen Dimov
  2 siblings, 1 reply; 39+ messages in thread
From: Nicolas Pitre @ 2010-11-30 19:57 UTC (permalink / raw)
  To: Daniel Walker
  Cc: linux-kernel, linux-arm-msm, Tony Lindgren, Arnd Bergmann,
	Greg Kroah-Hartman, Mike Frysinger, Andrew Morton, Alan Cox,
	Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On Tue, 30 Nov 2010, Daniel Walker wrote:

> This driver adds a basic console that uses the arm JTAG
> DCC to transfer data back and forth. It has support for
> ARMv6 and ARMv7.
> 
> This console is created under the HVC driver, and should be named
> /dev/hvcX (or /dev/hvc0 for example).
> 
> Cc: Tony Lindgren <tony@atomide.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Nicolas Pitre <nico@fluxnic.net>
> Cc: Greg Kroah-Hartman <gregkh@suse.de>
> Cc: Mike Frysinger <vapier@gentoo.org>
> Signed-off-by: Daniel Walker <dwalker@codeaurora.org>

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

This doesn't support both ARMv6 and ARMv7 at run time, but this can 
trivially be added later when needed.


Nicolas

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-11-30 19:57 ` Nicolas Pitre
@ 2010-11-30 21:17   ` Arnd Bergmann
  0 siblings, 0 replies; 39+ messages in thread
From: Arnd Bergmann @ 2010-11-30 21:17 UTC (permalink / raw)
  To: Nicolas Pitre
  Cc: Daniel Walker, linux-kernel, linux-arm-msm, Tony Lindgren,
	Greg Kroah-Hartman, Mike Frysinger, Andrew Morton, Alan Cox,
	Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On Tuesday 30 November 2010, Nicolas Pitre wrote:
> > Cc: Tony Lindgren <tony@atomide.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Nicolas Pitre <nico@fluxnic.net>
> > Cc: Greg Kroah-Hartman <gregkh@suse.de>
> > Cc: Mike Frysinger <vapier@gentoo.org>
> > Signed-off-by: Daniel Walker <dwalker@codeaurora.org>
> 
> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

Acked-by: Arnd Bergmann <arnd@arndb.de>

> This doesn't support both ARMv6 and ARMv7 at run time, but this can 
> trivially be added later when needed.

I was about to make a similar comment when I saw yours ;-)

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-11-30 19:25 [PATCH] drivers: char: hvc: add arm JTAG DCC console support Daniel Walker
  2010-11-30 19:57 ` Nicolas Pitre
@ 2010-12-01  5:30 ` Stephen Boyd
  2010-12-01 18:54   ` Daniel Walker
  2011-04-07 18:39 ` RONETIX - Asen Dimov
  2 siblings, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2010-12-01  5:30 UTC (permalink / raw)
  To: Daniel Walker
  Cc: linux-kernel, linux-arm-msm, Tony Lindgren, Arnd Bergmann,
	Nicolas Pitre, Greg Kroah-Hartman, Mike Frysinger, Andrew Morton,
	Alan Cox, Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On 11/30/2010 11:25 AM, Daniel Walker wrote:
> @@ -682,6 +682,15 @@ config HVC_UDBG
>         select HVC_DRIVER
>         default n
>  
> +config HVC_DCC
> +       bool "ARM JTAG DCC console"
> +       depends on ARM
> +       select HVC_DRIVER
> +       help
> +         This console uses the JTAG DCC on ARM to create a console under the HVC

Looks like you added one too many spaces for indent here.

> diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
> new file mode 100644
> index 0000000..6470f63
> --- /dev/null
> +++ b/drivers/char/hvc_dcc.c
> +static inline u32 __dcc_getstatus(void)
> +{
> +	u32 __ret;
> +
> +	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
> +		: "=r" (__ret) : : "cc");
> +
> +	return __ret;
> +}

Without marking this asm volatile my compiler decides it can cache the
value of __ret in a register and then check the value of it continually
in hvc_dcc_put_chars() (I had to replace get_wait/put_wait with 1 and
fixup the branch otherwise my disassembler barfed on __dcc_(get|put)char).


00000000 <hvc_dcc_put_chars>:
   0:   ee103e11        mrc     14, 0, r3, cr0, cr1, {0}
   4:   e3a0c000        mov     ip, #0  ; 0x0
   8:   e2033202        and     r3, r3, #536870912      ; 0x20000000
   c:   ea000006        b       2c <hvc_dcc_put_chars+0x2c>
  10:   e3530000        cmp     r3, #0  ; 0x0
  14:   1afffffd        bne     10 <hvc_dcc_put_chars+0x10>
  18:   e7d1000c        ldrb    r0, [r1, ip]
  1c:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  20:   2afffffd        bcs     1c <hvc_dcc_put_chars+0x1c>
  24:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  28:   e28cc001        add     ip, ip, #1      ; 0x1
  2c:   e15c0002        cmp     ip, r2
  30:   bafffff6        blt     10 <hvc_dcc_put_chars+0x10>
  34:   e1a00002        mov     r0, r2
  38:   e12fff1e        bx      lr

As you can see, the value of the mrc is checked against DCC_STATUS_TX
(bit 29) and then stored in r3 for later use. Marking this volatile
produces the following:

00000000 <hvc_dcc_put_chars>:
   0:   e3a03000        mov     r3, #0  ; 0x0
   4:   ea000007        b       28 <hvc_dcc_put_chars+0x28>
   8:   ee100e11        mrc     14, 0, r0, cr0, cr1, {0}
   c:   e3100202        tst     r0, #536870912  ; 0x20000000
  10:   1afffffc        bne     8 <hvc_dcc_put_chars+0x8>
  14:   e7d10003        ldrb    r0, [r1, r3]
  18:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  1c:   2afffffd        bcs     18 <hvc_dcc_put_chars+0x18>
  20:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  24:   e2833001        add     r3, r3, #1      ; 0x1
  28:   e1530002        cmp     r3, r2
  2c:   bafffff5        blt     8 <hvc_dcc_put_chars+0x8>
  30:   e1a00002        mov     r0, r2
  34:   e12fff1e        bx      lr

which looks better.

I marked all the asm in this driver as volatile. Is that correct?

> +#if defined(CONFIG_CPU_V7)
> +static inline char __dcc_getchar(void)
> +{
> +	char __c;
> +
> +	asm("get_wait:	mrc p14, 0, pc, c0, c1, 0                          \n\
> +			bne get_wait                                       \n\
> +			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> +		: "=r" (__c) : : "cc");
> +
> +	return __c;
> +}
> +#else
> +static inline char __dcc_getchar(void)
> +{
> +	char __c;
> +
> +	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> +		: "=r" (__c));
> +
> +	return __c;
> +}
> +#endif
> +
> +#if defined(CONFIG_CPU_V7)
> +static inline void __dcc_putchar(char c)
> +{
> +	asm("put_wait:	mrc p14, 0, pc, c0, c1, 0                 \n\
> +			bcs put_wait                              \n\
> +			mcr p14, 0, %0, c0, c5, 0                   "
> +	: : "r" (c) : "cc");
> +}
> +#else
> +static inline void __dcc_putchar(char c)
> +{
> +	asm("mcr p14, 0, %0, c0, c5, 0	@ write a char"
> +		: /* no output register */
> +		: "r" (c));
> +}
> +#endif
> +

I don't think both the v7 and v6 functions are necessary. It seems I can
get away with just the second version of __dcc_(get|put)char() on a v7.
The mrc p14, 0, pc, c0, c1, 0 will assign the top 4 bits (31-28) to the
condition codes NZCV on v7. It also looks like on an ARM11 (a v6) will
also do the same thing if I read the manuals right. The test in the
inline assembly is saying, wait for a character to be ready or wait for
a character to be read then actually write a character or read one. The
code in hvc_dcc_put_chars() is already doing the same thing, albeit in a
slightly different form. Instead of getting the status bits put into the
condition codes and looping with bne or bcs it will read the register,
and it with bit 29 or bit 28 to see if it should wait and then continue
with the writing/reading. I think you can just drop the looping for the
v7 version of the functions and have this driver work on v6 and v7.
Alternatively, you can make some function that says tx buffer is empty,
rx buffer is full or something but I don't see how saving a couple
instructions buys us much when we can have one driver for v6 and v7.

I see that Tony Lindgren modified the DCC macros for v7 in commit
200b7a8 (ARM: 5884/1: arm: Fix DCC console for v7, 2010-01-19). I'm not
sure why though, since it seems that a v6 and a v7 should really do the
same thing by waiting for the buffers to be ready before filling them or
reading them. Which probably means we can get low-level dcc debugging on
all targets if I'm not mistaken.

> +static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
> +{
> +	int i;
> +
> +	for (i = 0; i < count; i++) {
> +		while (__dcc_getstatus() & DCC_STATUS_TX)
> +			cpu_relax();
> +
> +		__dcc_putchar((char)(buf[i] & 0xFF));

Is this & 0xFF and cast to char unnecessary? buf is a char array, and
chars are always 8 bits. Can't we just do __dcc_putchar(buf[i])?

> +static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
> +{
> +	int i;
> +
> +	for (i = 0; i < count; ++i) {
> +		int c = -1;
> +
> +		if (__dcc_getstatus() & DCC_STATUS_RX)
> +			c = __dcc_getchar();
> +		if (c < 0)
> +			break;
> +		buf[i] = c;
> +	}

I think this for loop can be simplified. __dcc_getchar() returns a char.
It never returns -1, so the check for c < 0 can't be taken if
__dcc_getstatus() & DCC_STATUS_RX is true. The only case you break the
loop in then is if __dcc_getstatus() & DCC_STATUS_RX is false. So you
can have a simple if-else and assign buf[i] in the if branch and break
in the else branch.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-12-01  5:30 ` Stephen Boyd
@ 2010-12-01 18:54   ` Daniel Walker
  2010-12-01 19:28     ` Greg KH
  2010-12-01 20:20     ` [PATCH] drivers: char: hvc: add arm JTAG DCC console support Stephen Boyd
  0 siblings, 2 replies; 39+ messages in thread
From: Daniel Walker @ 2010-12-01 18:54 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: linux-kernel, linux-arm-msm, Tony Lindgren, Arnd Bergmann,
	Nicolas Pitre, Greg Kroah-Hartman, Mike Frysinger, Andrew Morton,
	Alan Cox, Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On Tue, 2010-11-30 at 21:30 -0800, Stephen Boyd wrote:
> On 11/30/2010 11:25 AM, Daniel Walker wrote:
> > @@ -682,6 +682,15 @@ config HVC_UDBG
> >         select HVC_DRIVER
> >         default n
> >  
> > +config HVC_DCC
> > +       bool "ARM JTAG DCC console"
> > +       depends on ARM
> > +       select HVC_DRIVER
> > +       help
> > +         This console uses the JTAG DCC on ARM to create a console under the HVC
> 
> Looks like you added one too many spaces for indent here.

The first line is fine, but the other two might need an extra space.

> > diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
> > new file mode 100644
> > index 0000000..6470f63
> > --- /dev/null
> > +++ b/drivers/char/hvc_dcc.c
> > +static inline u32 __dcc_getstatus(void)
> > +{
> > +	u32 __ret;
> > +
> > +	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
> > +		: "=r" (__ret) : : "cc");
> > +
> > +	return __ret;
> > +}
> 
> Without marking this asm volatile my compiler decides it can cache the
> value of __ret in a register and then check the value of it continually
> in hvc_dcc_put_chars() (I had to replace get_wait/put_wait with 1 and
> fixup the branch otherwise my disassembler barfed on __dcc_(get|put)char).
> 
> 
> 00000000 <hvc_dcc_put_chars>:
>    0:   ee103e11        mrc     14, 0, r3, cr0, cr1, {0}
>    4:   e3a0c000        mov     ip, #0  ; 0x0
>    8:   e2033202        and     r3, r3, #536870912      ; 0x20000000
>    c:   ea000006        b       2c <hvc_dcc_put_chars+0x2c>
>   10:   e3530000        cmp     r3, #0  ; 0x0
>   14:   1afffffd        bne     10 <hvc_dcc_put_chars+0x10>
>   18:   e7d1000c        ldrb    r0, [r1, ip]
>   1c:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
>   20:   2afffffd        bcs     1c <hvc_dcc_put_chars+0x1c>
>   24:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
>   28:   e28cc001        add     ip, ip, #1      ; 0x1
>   2c:   e15c0002        cmp     ip, r2
>   30:   bafffff6        blt     10 <hvc_dcc_put_chars+0x10>
>   34:   e1a00002        mov     r0, r2
>   38:   e12fff1e        bx      lr
> 
> As you can see, the value of the mrc is checked against DCC_STATUS_TX
> (bit 29) and then stored in r3 for later use. Marking this volatile
> produces the following:
> 
> 00000000 <hvc_dcc_put_chars>:
>    0:   e3a03000        mov     r3, #0  ; 0x0
>    4:   ea000007        b       28 <hvc_dcc_put_chars+0x28>
>    8:   ee100e11        mrc     14, 0, r0, cr0, cr1, {0}
>    c:   e3100202        tst     r0, #536870912  ; 0x20000000
>   10:   1afffffc        bne     8 <hvc_dcc_put_chars+0x8>
>   14:   e7d10003        ldrb    r0, [r1, r3]
>   18:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
>   1c:   2afffffd        bcs     18 <hvc_dcc_put_chars+0x18>
>   20:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
>   24:   e2833001        add     r3, r3, #1      ; 0x1
>   28:   e1530002        cmp     r3, r2
>   2c:   bafffff5        blt     8 <hvc_dcc_put_chars+0x8>
>   30:   e1a00002        mov     r0, r2
>   34:   e12fff1e        bx      lr
> 
> which looks better.
> 
> I marked all the asm in this driver as volatile. Is that correct?

Are you talking about __dcc_getstatus only? I don't think adding
volatile is going to hurt anything, if not having it causes problems.

> > +#if defined(CONFIG_CPU_V7)
> > +static inline char __dcc_getchar(void)
> > +{
> > +	char __c;
> > +
> > +	asm("get_wait:	mrc p14, 0, pc, c0, c1, 0                          \n\
> > +			bne get_wait                                       \n\
> > +			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> > +		: "=r" (__c) : : "cc");
> > +
> > +	return __c;
> > +}
> > +#else
> > +static inline char __dcc_getchar(void)
> > +{
> > +	char __c;
> > +
> > +	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> > +		: "=r" (__c));
> > +
> > +	return __c;
> > +}
> > +#endif
> > +
> > +#if defined(CONFIG_CPU_V7)
> > +static inline void __dcc_putchar(char c)
> > +{
> > +	asm("put_wait:	mrc p14, 0, pc, c0, c1, 0                 \n\
> > +			bcs put_wait                              \n\
> > +			mcr p14, 0, %0, c0, c5, 0                   "
> > +	: : "r" (c) : "cc");
> > +}
> > +#else
> > +static inline void __dcc_putchar(char c)
> > +{
> > +	asm("mcr p14, 0, %0, c0, c5, 0	@ write a char"
> > +		: /* no output register */
> > +		: "r" (c));
> > +}
> > +#endif
> > +
> 
> I don't think both the v7 and v6 functions are necessary. It seems I can
> get away with just the second version of __dcc_(get|put)char() on a v7.
> The mrc p14, 0, pc, c0, c1, 0 will assign the top 4 bits (31-28) to the
> condition codes NZCV on v7. It also looks like on an ARM11 (a v6) will
> also do the same thing if I read the manuals right. The test in the
> inline assembly is saying, wait for a character to be ready or wait for
> a character to be read then actually write a character or read one. The
> code in hvc_dcc_put_chars() is already doing the same thing, albeit in a
> slightly different form. Instead of getting the status bits put into the
> condition codes and looping with bne or bcs it will read the register,
> and it with bit 29 or bit 28 to see if it should wait and then continue
> with the writing/reading. I think you can just drop the looping for the
> v7 version of the functions and have this driver work on v6 and v7.

We could maybe drop the looping for TX, but RX has no C based looping
even tho for v7 it's recommended that we loop (presumably for v6 it's
not recommended).

> Alternatively, you can make some function that says tx buffer is empty,
> rx buffer is full or something but I don't see how saving a couple
> instructions buys us much when we can have one driver for v6 and v7.
> 
> I see that Tony Lindgren modified the DCC macros for v7 in commit
> 200b7a8 (ARM: 5884/1: arm: Fix DCC console for v7, 2010-01-19). I'm not
> sure why though, since it seems that a v6 and a v7 should really do the
> same thing by waiting for the buffers to be ready before filling them or
> reading them. Which probably means we can get low-level dcc debugging on
> all targets if I'm not mistaken.

This is primarily why these function look they way they do. I'd like to
hear from Tony, because he apparent didn't think they did the same
thing.

> > +static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < count; i++) {
> > +		while (__dcc_getstatus() & DCC_STATUS_TX)
> > +			cpu_relax();
> > +
> > +		__dcc_putchar((char)(buf[i] & 0xFF));
> 
> Is this & 0xFF and cast to char unnecessary? buf is a char array, and
> chars are always 8 bits. Can't we just do __dcc_putchar(buf[i])?

Yeah, doesn't seem like it.

> > +static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < count; ++i) {
> > +		int c = -1;
> > +
> > +		if (__dcc_getstatus() & DCC_STATUS_RX)
> > +			c = __dcc_getchar();
> > +		if (c < 0)
> > +			break;
> > +		buf[i] = c;
> > +	}
> 
> I think this for loop can be simplified. __dcc_getchar() returns a char.
> It never returns -1, so the check for c < 0 can't be taken if
> __dcc_getstatus() & DCC_STATUS_RX is true. The only case you break the
> loop in then is if __dcc_getstatus() & DCC_STATUS_RX is false. So you
> can have a simple if-else and assign buf[i] in the if branch and break
> in the else branch.
> 

Like this?

	for (i = 0; i < count; ++i) {

		if (__dcc_getstatus() & DCC_STATUS_RX)
			buf[i] = __dcc_getchar();
		else
			break;
	}

It's a micro clean up I guess ..

Daniel
-- 

Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-12-01 18:54   ` Daniel Walker
@ 2010-12-01 19:28     ` Greg KH
  2010-12-18  5:16       ` [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
  2010-12-01 20:20     ` [PATCH] drivers: char: hvc: add arm JTAG DCC console support Stephen Boyd
  1 sibling, 1 reply; 39+ messages in thread
From: Greg KH @ 2010-12-01 19:28 UTC (permalink / raw)
  To: Daniel Walker
  Cc: Stephen Boyd, linux-kernel, linux-arm-msm, Tony Lindgren,
	Arnd Bergmann, Nicolas Pitre, Mike Frysinger, Andrew Morton,
	Alan Cox, Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On Wed, Dec 01, 2010 at 10:54:56AM -0800, Daniel Walker wrote:
> On Tue, 2010-11-30 at 21:30 -0800, Stephen Boyd wrote:
> > On 11/30/2010 11:25 AM, Daniel Walker wrote:
> > > @@ -682,6 +682,15 @@ config HVC_UDBG
> > >         select HVC_DRIVER
> > >         default n
> > >  
> > > +config HVC_DCC
> > > +       bool "ARM JTAG DCC console"
> > > +       depends on ARM
> > > +       select HVC_DRIVER
> > > +       help
> > > +         This console uses the JTAG DCC on ARM to create a console under the HVC
> > 
> > Looks like you added one too many spaces for indent here.
> 
> The first line is fine, but the other two might need an extra space.

For this, or any other changes you want, I'll gladly take a follow-on
patch as this one is already in my tty-next tree.

thanks,

greg k-h

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-12-01 18:54   ` Daniel Walker
  2010-12-01 19:28     ` Greg KH
@ 2010-12-01 20:20     ` Stephen Boyd
  2010-12-07 19:10       ` Stephen Boyd
  1 sibling, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2010-12-01 20:20 UTC (permalink / raw)
  To: Daniel Walker, Tony Lindgren
  Cc: linux-kernel, linux-arm-msm, Arnd Bergmann, Nicolas Pitre,
	Greg Kroah-Hartman, Mike Frysinger, Andrew Morton, Alan Cox,
	Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On 12/01/2010 10:54 AM, Daniel Walker wrote:
> Are you talking about __dcc_getstatus only? I don't think adding
> volatile is going to hurt anything, if not having it causes problems.
>

Just marking __dcc_getstatus volatile gives me

00000038 <hvc_dcc_get_chars>:
  38:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  3c:   1afffffd        bne     38 <hvc_dcc_get_chars>
  40:   ee103e15        mrc     14, 0, r3, cr0, cr5, {0}
  44:   e3a00000        mov     r0, #0  ; 0x0
  48:   e6ef3073        uxtb    r3, r3
  4c:   ea000004        b       64 <hvc_dcc_get_chars+0x2c>
  50:   ee10ce11        mrc     14, 0, ip, cr0, cr1, {0}
  54:   e31c0101        tst     ip, #1073741824 ; 0x40000000
  58:   012fff1e        bxeq    lr
  5c:   e7c13000        strb    r3, [r1, r0]
  60:   e2800001        add     r0, r0, #1      ; 0x1
  64:   e1500002        cmp     r0, r2
  68:   bafffff8        blt     50 <hvc_dcc_get_chars+0x18>
  6c:   e12fff1e        bx      lr

Seems the compiler keeps the value of __dcc_getchar() in r3 for the
duration of the loop. So we need to mark that one volatile too. I don't
think __dcc_putchar() needs to be marked volatile but it probably
doesn't hurt.

>
> We could maybe drop the looping for TX, but RX has no C based looping
> even tho for v7 it's recommended that we loop (presumably for v6 it's
> not recommended).
>

Definitely for TX since it seems like a redundant loop, but I agree RX
code has changed. Instead of

If RX buffer full
Poll for RX buffer full
Read character from RX buffer

we would have

If RX buffer full
Read character from RX buffer

which doesn't seem all that different assuming the RX buffer doesn't go
from full to empty between the If and Poll steps. Hopefully Tony knows more.

> Like this?
>
> 	for (i = 0; i < count; ++i) {
>
> 		if (__dcc_getstatus() & DCC_STATUS_RX)
> 			buf[i] = __dcc_getchar();
> 		else
> 			break;
> 	}
>
> It's a micro clean up I guess ..

Yes, it's much clearer that way.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-12-01 20:20     ` [PATCH] drivers: char: hvc: add arm JTAG DCC console support Stephen Boyd
@ 2010-12-07 19:10       ` Stephen Boyd
  2011-01-14 19:19         ` Tony Lindgren
  0 siblings, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2010-12-07 19:10 UTC (permalink / raw)
  To: Tony Lindgren
  Cc: Daniel Walker, linux-kernel, linux-arm-msm, Arnd Bergmann,
	Nicolas Pitre, Greg Kroah-Hartman, Mike Frysinger, Andrew Morton,
	Alan Cox, Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On 12/01/2010 12:20 PM, Stephen Boyd wrote:
> Definitely for TX since it seems like a redundant loop, but I agree RX
> code has changed. Instead of
>
> If RX buffer full
> Poll for RX buffer full
> Read character from RX buffer
>
> we would have
>
> If RX buffer full
> Read character from RX buffer
>
> which doesn't seem all that different assuming the RX buffer doesn't go
> from full to empty between the If and Poll steps. Hopefully Tony knows more.
>

Tony, any thoughts?

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2010-12-01 19:28     ` Greg KH
@ 2010-12-18  5:16       ` Stephen Boyd
  2010-12-20 17:51         ` Daniel Walker
  2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
  0 siblings, 2 replies; 39+ messages in thread
From: Stephen Boyd @ 2010-12-18  5:16 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: linux-kernel, linux-arm-msm, linux-arm-kernel, Tony Lindgren,
	Arnd Bergmann, Nicolas Pitre, Daniel Walker

The inline assembly differences for v6 vs. v7 in the hvc_dcc
driver are purely optimizations. On a v7 processor, an mrc with
the pc sets the condition codes to the 28-31 bits of the register
being read. It just so happens that the TX/RX full bits the DCC
driver is testing for are high enough in the register to be put
into the condition codes. On a v6 processor, this "feature" isn't
implemented and thus we have to do the usual read, mask, test
operations to check for TX/RX full.

Since we already test the RX/TX full bits before calling
__dcc_getchar() and __dcc_putchar() we don't actually need to do
anything special for v7 over v6. The only difference is in
hvc_dcc_get_chars(). We would test RX full, poll RX full, and
then read a character from the buffer, whereas now we will test
RX full, read a character from the buffer, and then test RX full
again for the second iteration of the loop. It doesn't seem
possible for the buffer to go from full to empty between testing
the RX full and reading a character. Therefore, replace the v7
versions with the v6 versions and everything works the same.

While we're here, cleanup the for loops a bit and mark the inline
assembly as volatile. Not marking it volatile causes GCC to cache
the results of the status and RX buffer registers causing
lockups.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/char/hvc_dcc.c |   43 +++++++------------------------------------
 1 files changed, 7 insertions(+), 36 deletions(-)

diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
index 6470f63..435f6fa 100644
--- a/drivers/char/hvc_dcc.c
+++ b/drivers/char/hvc_dcc.c
@@ -33,54 +33,29 @@
 static inline u32 __dcc_getstatus(void)
 {
 	u32 __ret;
-
-	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
+	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
 		: "=r" (__ret) : : "cc");
 
 	return __ret;
 }
 
 
-#if defined(CONFIG_CPU_V7)
 static inline char __dcc_getchar(void)
 {
 	char __c;
 
-	asm("get_wait:	mrc p14, 0, pc, c0, c1, 0                          \n\
-			bne get_wait                                       \n\
-			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
-		: "=r" (__c) : : "cc");
-
-	return __c;
-}
-#else
-static inline char __dcc_getchar(void)
-{
-	char __c;
-
-	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
+	asm volatile("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
 		: "=r" (__c));
 
 	return __c;
 }
-#endif
 
-#if defined(CONFIG_CPU_V7)
-static inline void __dcc_putchar(char c)
-{
-	asm("put_wait:	mrc p14, 0, pc, c0, c1, 0                 \n\
-			bcs put_wait                              \n\
-			mcr p14, 0, %0, c0, c5, 0                   "
-	: : "r" (c) : "cc");
-}
-#else
 static inline void __dcc_putchar(char c)
 {
-	asm("mcr p14, 0, %0, c0, c5, 0	@ write a char"
+	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
 		: /* no output register */
 		: "r" (c));
 }
-#endif
 
 static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
 {
@@ -90,7 +65,7 @@ static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
 		while (__dcc_getstatus() & DCC_STATUS_TX)
 			cpu_relax();
 
-		__dcc_putchar((char)(buf[i] & 0xFF));
+		__dcc_putchar(buf[i]);
 	}
 
 	return count;
@@ -100,15 +75,11 @@ static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
 {
 	int i;
 
-	for (i = 0; i < count; ++i) {
-		int c = -1;
-
+	for (i = 0; i < count; ++i)
 		if (__dcc_getstatus() & DCC_STATUS_RX)
-			c = __dcc_getchar();
-		if (c < 0)
+			buf[i] = __dcc_getchar();
+		else
 			break;
-		buf[i] = c;
-	}
 
 	return i;
 }
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2010-12-18  5:16       ` [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
@ 2010-12-20 17:51         ` Daniel Walker
  2010-12-20 18:39           ` Stephen Boyd
  2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
  1 sibling, 1 reply; 39+ messages in thread
From: Daniel Walker @ 2010-12-20 17:51 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Nicolas Pitre

On Fri, 2010-12-17 at 21:16 -0800, Stephen Boyd wrote:
> The inline assembly differences for v6 vs. v7 in the hvc_dcc
> driver are purely optimizations. On a v7 processor, an mrc with
> the pc sets the condition codes to the 28-31 bits of the register
> being read. It just so happens that the TX/RX full bits the DCC
> driver is testing for are high enough in the register to be put
> into the condition codes. On a v6 processor, this "feature" isn't
> implemented and thus we have to do the usual read, mask, test
> operations to check for TX/RX full.
> 
> Since we already test the RX/TX full bits before calling
> __dcc_getchar() and __dcc_putchar() we don't actually need to do
> anything special for v7 over v6. The only difference is in
> hvc_dcc_get_chars(). We would test RX full, poll RX full, and
> then read a character from the buffer, whereas now we will test
> RX full, read a character from the buffer, and then test RX full
> again for the second iteration of the loop. It doesn't seem
> possible for the buffer to go from full to empty between testing
> the RX full and reading a character. Therefore, replace the v7
> versions with the v6 versions and everything works the same.
> 
> While we're here, cleanup the for loops a bit and mark the inline
> assembly as volatile. Not marking it volatile causes GCC to cache
> the results of the status and RX buffer registers causing
> lockups.

I would expect to see three patches. One that adds volatile, which
appears to be a good fix. Another patch that changes the assembly lines,
and another that does the clean up. The last two are more controversial
ones.

Daniel

-- 
Sent by an consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum.



^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2010-12-20 17:51         ` Daniel Walker
@ 2010-12-20 18:39           ` Stephen Boyd
  2010-12-20 18:46             ` Nicolas Pitre
  0 siblings, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2010-12-20 18:39 UTC (permalink / raw)
  To: Daniel Walker
  Cc: Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Nicolas Pitre

On 12/20/2010 09:51 AM, Daniel Walker wrote:
>
> I would expect to see three patches. One that adds volatile, which
> appears to be a good fix. Another patch that changes the assembly lines,
> and another that does the clean up. The last two are more controversial
> ones

Ok. I'll send a series later today to give some more time for feedback.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2010-12-20 18:39           ` Stephen Boyd
@ 2010-12-20 18:46             ` Nicolas Pitre
  0 siblings, 0 replies; 39+ messages in thread
From: Nicolas Pitre @ 2010-12-20 18:46 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Daniel Walker, Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann

On Mon, 20 Dec 2010, Stephen Boyd wrote:

> On 12/20/2010 09:51 AM, Daniel Walker wrote:
> >
> > I would expect to see three patches. One that adds volatile, which
> > appears to be a good fix. Another patch that changes the assembly lines,
> > and another that does the clean up. The last two are more controversial
> > ones
> 
> Ok. I'll send a series later today to give some more time for feedback.

I think you can do that right away.  Splitting the patch will make that 
feedback easier to provide.


Nicolas

^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCH 0/3] hvc_dcc cleanups and fixes
  2010-12-18  5:16       ` [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
  2010-12-20 17:51         ` Daniel Walker
@ 2010-12-20 20:08         ` Stephen Boyd
  2010-12-20 20:08           ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
                             ` (4 more replies)
  1 sibling, 5 replies; 39+ messages in thread
From: Stephen Boyd @ 2010-12-20 20:08 UTC (permalink / raw)
  To: Greg Kroah-Hartman; +Cc: linux-kernel, linux-arm-msm, linux-arm-kernel

Here are the split patches.

The first two patches cleanup and fix the hvc_dcc driver for my
compiler. The final patch is more controversial, it removes the
v6 and v7 differences in this driver.

Stephen Boyd (3):
  hvc_dcc: Fix bad code generation by marking assembly volatile
  hvc_dcc: Simplify put_chars()/get_chars() loops
  hvc_dcc: Simplify assembly for v6 and v7 ARM

 drivers/char/hvc_dcc.c |   43 +++++++------------------------------------
 1 files changed, 7 insertions(+), 36 deletions(-)

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
@ 2010-12-20 20:08           ` Stephen Boyd
  2010-12-20 21:39             ` Nicolas Pitre
  2010-12-20 21:49             ` Arnaud Lacombe
  2010-12-20 20:08           ` [PATCH 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
                             ` (3 subsequent siblings)
  4 siblings, 2 replies; 39+ messages in thread
From: Stephen Boyd @ 2010-12-20 20:08 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: linux-kernel, linux-arm-msm, linux-arm-kernel, Tony Lindgren,
	Arnd Bergmann, Nicolas Pitre, Daniel Walker

Without marking the asm __dcc_getstatus() volatile my compiler
decides it can cache the value of __ret in a register and then
check the value of it continually in hvc_dcc_put_chars() (I had
to replace get_wait/put_wait with 1 and fixup the branch
otherwise my disassembler barfed on __dcc_(get|put)char).

00000000 <hvc_dcc_put_chars>:
   0:   ee103e11        mrc     14, 0, r3, cr0, cr1, {0}
   4:   e3a0c000        mov     ip, #0  ; 0x0
   8:   e2033202        and     r3, r3, #536870912      ; 0x20000000
   c:   ea000006        b       2c <hvc_dcc_put_chars+0x2c>
  10:   e3530000        cmp     r3, #0  ; 0x0
  14:   1afffffd        bne     10 <hvc_dcc_put_chars+0x10>
  18:   e7d1000c        ldrb    r0, [r1, ip]
  1c:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  20:   2afffffd        bcs     1c <hvc_dcc_put_chars+0x1c>
  24:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  28:   e28cc001        add     ip, ip, #1      ; 0x1
  2c:   e15c0002        cmp     ip, r2
  30:   bafffff6        blt     10 <hvc_dcc_put_chars+0x10>
  34:   e1a00002        mov     r0, r2
  38:   e12fff1e        bx      lr

As you can see, the value of the mrc is checked against
DCC_STATUS_TX (bit 29) and then stored in r3 for later use.
Marking the asm volatile produces the following:

00000000 <hvc_dcc_put_chars>:
   0:   e3a03000        mov     r3, #0  ; 0x0
   4:   ea000007        b       28 <hvc_dcc_put_chars+0x28>
   8:   ee100e11        mrc     14, 0, r0, cr0, cr1, {0}
   c:   e3100202        tst     r0, #536870912  ; 0x20000000
  10:   1afffffc        bne     8 <hvc_dcc_put_chars+0x8>
  14:   e7d10003        ldrb    r0, [r1, r3]
  18:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  1c:   2afffffd        bcs     18 <hvc_dcc_put_chars+0x18>
  20:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  24:   e2833001        add     r3, r3, #1      ; 0x1
  28:   e1530002        cmp     r3, r2
  2c:   bafffff5        blt     8 <hvc_dcc_put_chars+0x8>
  30:   e1a00002        mov     r0, r2
  34:   e12fff1e        bx      lr

which looks better and actually works. Mark all the inline
assembly in this file as volatile since we don't want the
compiler to optimize away these statements or move them around
in any way.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/char/hvc_dcc.c |   11 +++++------
 1 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
index 6470f63..155ec10 100644
--- a/drivers/char/hvc_dcc.c
+++ b/drivers/char/hvc_dcc.c
@@ -33,8 +33,7 @@
 static inline u32 __dcc_getstatus(void)
 {
 	u32 __ret;
-
-	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
+	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
 		: "=r" (__ret) : : "cc");
 
 	return __ret;
@@ -46,7 +45,7 @@ static inline char __dcc_getchar(void)
 {
 	char __c;
 
-	asm("get_wait:	mrc p14, 0, pc, c0, c1, 0                          \n\
+	asm volatile("get_wait:	mrc p14, 0, pc, c0, c1, 0                  \n\
 			bne get_wait                                       \n\
 			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
 		: "=r" (__c) : : "cc");
@@ -58,7 +57,7 @@ static inline char __dcc_getchar(void)
 {
 	char __c;
 
-	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
+	asm volatile("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
 		: "=r" (__c));
 
 	return __c;
@@ -68,7 +67,7 @@ static inline char __dcc_getchar(void)
 #if defined(CONFIG_CPU_V7)
 static inline void __dcc_putchar(char c)
 {
-	asm("put_wait:	mrc p14, 0, pc, c0, c1, 0                 \n\
+	asm volatile("put_wait:	mrc p14, 0, pc, c0, c1, 0         \n\
 			bcs put_wait                              \n\
 			mcr p14, 0, %0, c0, c5, 0                   "
 	: : "r" (c) : "cc");
@@ -76,7 +75,7 @@ static inline void __dcc_putchar(char c)
 #else
 static inline void __dcc_putchar(char c)
 {
-	asm("mcr p14, 0, %0, c0, c5, 0	@ write a char"
+	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
 		: /* no output register */
 		: "r" (c));
 }
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCH 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops
  2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
  2010-12-20 20:08           ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
@ 2010-12-20 20:08           ` Stephen Boyd
  2010-12-20 20:08           ` [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
                             ` (2 subsequent siblings)
  4 siblings, 0 replies; 39+ messages in thread
From: Stephen Boyd @ 2010-12-20 20:08 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: linux-kernel, linux-arm-msm, linux-arm-kernel, Daniel Walker

Casting and anding with 0xff is unnecessary in
hvc_dcc_put_chars() since buf is already a char[].
__dcc_get_char() can't return an int less than 0 since it only
returns a char. Simplify the if statement in hvc_dcc_get_chars()
to take this into account.

Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/char/hvc_dcc.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
index 155ec10..ad23cc8 100644
--- a/drivers/char/hvc_dcc.c
+++ b/drivers/char/hvc_dcc.c
@@ -89,7 +89,7 @@ static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
 		while (__dcc_getstatus() & DCC_STATUS_TX)
 			cpu_relax();
 
-		__dcc_putchar((char)(buf[i] & 0xFF));
+		__dcc_putchar(buf[i]);
 	}
 
 	return count;
@@ -99,15 +99,11 @@ static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
 {
 	int i;
 
-	for (i = 0; i < count; ++i) {
-		int c = -1;
-
+	for (i = 0; i < count; ++i)
 		if (__dcc_getstatus() & DCC_STATUS_RX)
-			c = __dcc_getchar();
-		if (c < 0)
+			buf[i] = __dcc_getchar();
+		else
 			break;
-		buf[i] = c;
-	}
 
 	return i;
 }
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
  2010-12-20 20:08           ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
  2010-12-20 20:08           ` [PATCH 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
@ 2010-12-20 20:08           ` Stephen Boyd
  2010-12-20 21:44             ` Nicolas Pitre
  2011-01-06  1:49           ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
  2011-02-03 22:17           ` Greg KH
  4 siblings, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2010-12-20 20:08 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: linux-kernel, linux-arm-msm, linux-arm-kernel, Tony Lindgren,
	Arnd Bergmann, Nicolas Pitre, Daniel Walker

The inline assembly differences for v6 vs. v7 in the hvc_dcc
driver are purely optimizations. On a v7 processor, an mrc with
the pc sets the condition codes to the 28-31 bits of the register
being read. It just so happens that the TX/RX full bits the DCC
driver is testing for are high enough in the register to be put
into the condition codes. On a v6 processor, this "feature" isn't
implemented and thus we have to do the usual read, mask, test
operations to check for TX/RX full.

Since we already test the RX/TX full bits before calling
__dcc_getchar() and __dcc_putchar() we don't actually need to do
anything special for v7 over v6. The only difference is in
hvc_dcc_get_chars(). We would test RX full, poll RX full, and
then read a character from the buffer, whereas now we will test
RX full, read a character from the buffer, and then test RX full
again for the second iteration of the loop. It doesn't seem
possible for the buffer to go from full to empty between testing
the RX full and reading a character. Therefore, replace the v7
versions with the v6 versions and everything works the same.

Cc: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/char/hvc_dcc.c |   24 ------------------------
 1 files changed, 0 insertions(+), 24 deletions(-)

diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
index ad23cc8..435f6fa 100644
--- a/drivers/char/hvc_dcc.c
+++ b/drivers/char/hvc_dcc.c
@@ -40,19 +40,6 @@ static inline u32 __dcc_getstatus(void)
 }
 
 
-#if defined(CONFIG_CPU_V7)
-static inline char __dcc_getchar(void)
-{
-	char __c;
-
-	asm volatile("get_wait:	mrc p14, 0, pc, c0, c1, 0                  \n\
-			bne get_wait                                       \n\
-			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
-		: "=r" (__c) : : "cc");
-
-	return __c;
-}
-#else
 static inline char __dcc_getchar(void)
 {
 	char __c;
@@ -62,24 +49,13 @@ static inline char __dcc_getchar(void)
 
 	return __c;
 }
-#endif
 
-#if defined(CONFIG_CPU_V7)
-static inline void __dcc_putchar(char c)
-{
-	asm volatile("put_wait:	mrc p14, 0, pc, c0, c1, 0         \n\
-			bcs put_wait                              \n\
-			mcr p14, 0, %0, c0, c5, 0                   "
-	: : "r" (c) : "cc");
-}
-#else
 static inline void __dcc_putchar(char c)
 {
 	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
 		: /* no output register */
 		: "r" (c));
 }
-#endif
 
 static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
 {
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2010-12-20 20:08           ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
@ 2010-12-20 21:39             ` Nicolas Pitre
  2011-01-02  9:00               ` Pavel Machek
  2011-01-04 18:49               ` Tony Lindgren
  2010-12-20 21:49             ` Arnaud Lacombe
  1 sibling, 2 replies; 39+ messages in thread
From: Nicolas Pitre @ 2010-12-20 21:39 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Daniel Walker

On Mon, 20 Dec 2010, Stephen Boyd wrote:

> Without marking the asm __dcc_getstatus() volatile my compiler
> decides it can cache the value of __ret in a register and then
> check the value of it continually in hvc_dcc_put_chars() (I had
> to replace get_wait/put_wait with 1 and fixup the branch
> otherwise my disassembler barfed on __dcc_(get|put)char).
> 
> 00000000 <hvc_dcc_put_chars>:
>    0:   ee103e11        mrc     14, 0, r3, cr0, cr1, {0}
>    4:   e3a0c000        mov     ip, #0  ; 0x0
>    8:   e2033202        and     r3, r3, #536870912      ; 0x20000000
>    c:   ea000006        b       2c <hvc_dcc_put_chars+0x2c>
>   10:   e3530000        cmp     r3, #0  ; 0x0
>   14:   1afffffd        bne     10 <hvc_dcc_put_chars+0x10>
>   18:   e7d1000c        ldrb    r0, [r1, ip]
>   1c:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
>   20:   2afffffd        bcs     1c <hvc_dcc_put_chars+0x1c>
>   24:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
>   28:   e28cc001        add     ip, ip, #1      ; 0x1
>   2c:   e15c0002        cmp     ip, r2
>   30:   bafffff6        blt     10 <hvc_dcc_put_chars+0x10>
>   34:   e1a00002        mov     r0, r2
>   38:   e12fff1e        bx      lr
> 
> As you can see, the value of the mrc is checked against
> DCC_STATUS_TX (bit 29) and then stored in r3 for later use.
> Marking the asm volatile produces the following:
> 
> 00000000 <hvc_dcc_put_chars>:
>    0:   e3a03000        mov     r3, #0  ; 0x0
>    4:   ea000007        b       28 <hvc_dcc_put_chars+0x28>
>    8:   ee100e11        mrc     14, 0, r0, cr0, cr1, {0}
>    c:   e3100202        tst     r0, #536870912  ; 0x20000000
>   10:   1afffffc        bne     8 <hvc_dcc_put_chars+0x8>
>   14:   e7d10003        ldrb    r0, [r1, r3]
>   18:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
>   1c:   2afffffd        bcs     18 <hvc_dcc_put_chars+0x18>
>   20:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
>   24:   e2833001        add     r3, r3, #1      ; 0x1
>   28:   e1530002        cmp     r3, r2
>   2c:   bafffff5        blt     8 <hvc_dcc_put_chars+0x8>
>   30:   e1a00002        mov     r0, r2
>   34:   e12fff1e        bx      lr
> 
> which looks better and actually works. Mark all the inline
> assembly in this file as volatile since we don't want the
> compiler to optimize away these statements or move them around
> in any way.
> 
> Cc: Tony Lindgren <tony@atomide.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
> Cc: Daniel Walker <dwalker@codeaurora.org>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>


> ---
>  drivers/char/hvc_dcc.c |   11 +++++------
>  1 files changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
> index 6470f63..155ec10 100644
> --- a/drivers/char/hvc_dcc.c
> +++ b/drivers/char/hvc_dcc.c
> @@ -33,8 +33,7 @@
>  static inline u32 __dcc_getstatus(void)
>  {
>  	u32 __ret;
> -
> -	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
> +	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
>  		: "=r" (__ret) : : "cc");
>  
>  	return __ret;
> @@ -46,7 +45,7 @@ static inline char __dcc_getchar(void)
>  {
>  	char __c;
>  
> -	asm("get_wait:	mrc p14, 0, pc, c0, c1, 0                          \n\
> +	asm volatile("get_wait:	mrc p14, 0, pc, c0, c1, 0                  \n\
>  			bne get_wait                                       \n\
>  			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
>  		: "=r" (__c) : : "cc");
> @@ -58,7 +57,7 @@ static inline char __dcc_getchar(void)
>  {
>  	char __c;
>  
> -	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> +	asm volatile("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
>  		: "=r" (__c));
>  
>  	return __c;
> @@ -68,7 +67,7 @@ static inline char __dcc_getchar(void)
>  #if defined(CONFIG_CPU_V7)
>  static inline void __dcc_putchar(char c)
>  {
> -	asm("put_wait:	mrc p14, 0, pc, c0, c1, 0                 \n\
> +	asm volatile("put_wait:	mrc p14, 0, pc, c0, c1, 0         \n\
>  			bcs put_wait                              \n\
>  			mcr p14, 0, %0, c0, c5, 0                   "
>  	: : "r" (c) : "cc");
> @@ -76,7 +75,7 @@ static inline void __dcc_putchar(char c)
>  #else
>  static inline void __dcc_putchar(char c)
>  {
> -	asm("mcr p14, 0, %0, c0, c5, 0	@ write a char"
> +	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
>  		: /* no output register */
>  		: "r" (c));
>  }
> -- 
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
> 

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2010-12-20 20:08           ` [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
@ 2010-12-20 21:44             ` Nicolas Pitre
  2011-01-04 18:52               ` Tony Lindgren
  0 siblings, 1 reply; 39+ messages in thread
From: Nicolas Pitre @ 2010-12-20 21:44 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Daniel Walker

On Mon, 20 Dec 2010, Stephen Boyd wrote:

> The inline assembly differences for v6 vs. v7 in the hvc_dcc
> driver are purely optimizations. On a v7 processor, an mrc with
> the pc sets the condition codes to the 28-31 bits of the register
> being read. It just so happens that the TX/RX full bits the DCC
> driver is testing for are high enough in the register to be put
> into the condition codes. On a v6 processor, this "feature" isn't
> implemented and thus we have to do the usual read, mask, test
> operations to check for TX/RX full.
> 
> Since we already test the RX/TX full bits before calling
> __dcc_getchar() and __dcc_putchar() we don't actually need to do
> anything special for v7 over v6. The only difference is in
> hvc_dcc_get_chars(). We would test RX full, poll RX full, and
> then read a character from the buffer, whereas now we will test
> RX full, read a character from the buffer, and then test RX full
> again for the second iteration of the loop. It doesn't seem
> possible for the buffer to go from full to empty between testing
> the RX full and reading a character. Therefore, replace the v7
> versions with the v6 versions and everything works the same.
> 
> Cc: Tony Lindgren <tony@atomide.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
> Cc: Daniel Walker <dwalker@codeaurora.org>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

> ---
>  drivers/char/hvc_dcc.c |   24 ------------------------
>  1 files changed, 0 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
> index ad23cc8..435f6fa 100644
> --- a/drivers/char/hvc_dcc.c
> +++ b/drivers/char/hvc_dcc.c
> @@ -40,19 +40,6 @@ static inline u32 __dcc_getstatus(void)
>  }
>  
>  
> -#if defined(CONFIG_CPU_V7)
> -static inline char __dcc_getchar(void)
> -{
> -	char __c;
> -
> -	asm volatile("get_wait:	mrc p14, 0, pc, c0, c1, 0                  \n\
> -			bne get_wait                                       \n\
> -			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> -		: "=r" (__c) : : "cc");
> -
> -	return __c;
> -}
> -#else
>  static inline char __dcc_getchar(void)
>  {
>  	char __c;
> @@ -62,24 +49,13 @@ static inline char __dcc_getchar(void)
>  
>  	return __c;
>  }
> -#endif
>  
> -#if defined(CONFIG_CPU_V7)
> -static inline void __dcc_putchar(char c)
> -{
> -	asm volatile("put_wait:	mrc p14, 0, pc, c0, c1, 0         \n\
> -			bcs put_wait                              \n\
> -			mcr p14, 0, %0, c0, c5, 0                   "
> -	: : "r" (c) : "cc");
> -}
> -#else
>  static inline void __dcc_putchar(char c)
>  {
>  	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
>  		: /* no output register */
>  		: "r" (c));
>  }
> -#endif
>  
>  static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
>  {
> -- 
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
> 

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2010-12-20 20:08           ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
  2010-12-20 21:39             ` Nicolas Pitre
@ 2010-12-20 21:49             ` Arnaud Lacombe
  2010-12-20 21:52               ` Stephen Boyd
  1 sibling, 1 reply; 39+ messages in thread
From: Arnaud Lacombe @ 2010-12-20 21:49 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Nicolas Pitre,
	Daniel Walker

Hi,

On Mon, Dec 20, 2010 at 3:08 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
> Without marking the asm __dcc_getstatus() volatile my compiler
> decides [...]
What compiler ? That might be a usefull information to know,
espectially 5 years from now when tracing code history. There has been
similar issue with gcc 4.5 recently. AFAIK, in the same idea, the
final change has been to mark the asm volatile.

Thanks,
 - Arnaud

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2010-12-20 21:49             ` Arnaud Lacombe
@ 2010-12-20 21:52               ` Stephen Boyd
  2010-12-20 22:10                 ` Nicolas Pitre
  0 siblings, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2010-12-20 21:52 UTC (permalink / raw)
  To: Arnaud Lacombe
  Cc: Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Nicolas Pitre,
	Daniel Walker

On 12/20/2010 01:49 PM, Arnaud Lacombe wrote:
> Hi,
>
> On Mon, Dec 20, 2010 at 3:08 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
>> Without marking the asm __dcc_getstatus() volatile my compiler
>> decides [...]
> What compiler ? That might be a usefull information to know,
> espectially 5 years from now when tracing code history. There has been
> similar issue with gcc 4.5 recently. AFAIK, in the same idea, the
> final change has been to mark the asm volatile.

Sure, we can replace "my compiler" with "my compiler (arm-eabi-gcc (GCC)
4.4.0)".

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2010-12-20 21:52               ` Stephen Boyd
@ 2010-12-20 22:10                 ` Nicolas Pitre
  0 siblings, 0 replies; 39+ messages in thread
From: Nicolas Pitre @ 2010-12-20 22:10 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Arnaud Lacombe, Greg Kroah-Hartman, lkml, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Daniel Walker

On Mon, 20 Dec 2010, Stephen Boyd wrote:

> On 12/20/2010 01:49 PM, Arnaud Lacombe wrote:
> > Hi,
> >
> > On Mon, Dec 20, 2010 at 3:08 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
> >> Without marking the asm __dcc_getstatus() volatile my compiler
> >> decides [...]
> > What compiler ? That might be a usefull information to know,
> > espectially 5 years from now when tracing code history. There has been
> > similar issue with gcc 4.5 recently. AFAIK, in the same idea, the
> > final change has been to mark the asm volatile.
> 
> Sure, we can replace "my compiler" with "my compiler (arm-eabi-gcc (GCC)
> 4.4.0)".

Compiler version doesn't matter -- this is a simple correctness issue.

If an inline asm statement provides an output value then the compiler is 
free to cache that value in a register, unless the inline asm is marked 
so that the value may change from one invocation to another.  Also, the 
compiler is free to eliminate the inline asm statement entirely as well 
if the output value provided by that inline asm is never used... unless 
if the inline asm is marked as having side effects.  In both cases the 
volatile qualifier does indicate that the returned value may change 
(new status flag state) and 
that the asm code therein has side effects (e.g. pop a character off a 
FIFO).

Sometimes the desired effect can be indicated by clever usage of 
parameter constraints, but in this case the volatile keyword is most 
appropriate.


Nicolas

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2010-12-20 21:39             ` Nicolas Pitre
@ 2011-01-02  9:00               ` Pavel Machek
  2011-01-02 18:49                 ` David Brown
  2011-01-04 18:49               ` Tony Lindgren
  1 sibling, 1 reply; 39+ messages in thread
From: Pavel Machek @ 2011-01-02  9:00 UTC (permalink / raw)
  To: Nicolas Pitre
  Cc: Stephen Boyd, Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Tony Lindgren, Arnd Bergmann, Daniel Walker

Hi!

> > diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
> > index 6470f63..155ec10 100644
> > --- a/drivers/char/hvc_dcc.c
> > +++ b/drivers/char/hvc_dcc.c
> > @@ -33,8 +33,7 @@
> >  static inline u32 __dcc_getstatus(void)
> >  {
> >  	u32 __ret;
> > -
> > -	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
> > +	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
> >  		: "=r" (__ret) : : "cc");
> >  
> >  	return __ret;

Is volatile needed here? If __dcc_getstatus() return value is
discarded, we want assembly discarded, right?


> > @@ -58,7 +57,7 @@ static inline char __dcc_getchar(void)
> >  {
> >  	char __c;
> >  
> > -	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> > +	asm volatile("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
> >  		: "=r" (__c));
> >  
> >  	return __c;

Same here?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2011-01-02  9:00               ` Pavel Machek
@ 2011-01-02 18:49                 ` David Brown
  2011-01-03  5:50                   ` Pavel Machek
  0 siblings, 1 reply; 39+ messages in thread
From: David Brown @ 2011-01-02 18:49 UTC (permalink / raw)
  To: Pavel Machek
  Cc: Nicolas Pitre, Stephen Boyd, Greg Kroah-Hartman, linux-kernel,
	linux-arm-msm, linux-arm-kernel, Tony Lindgren, Arnd Bergmann,
	Daniel Walker

On Sun, Jan 02 2011, Pavel Machek wrote:

>> > diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
>> > index 6470f63..155ec10 100644
>> > --- a/drivers/char/hvc_dcc.c
>> > +++ b/drivers/char/hvc_dcc.c
>> > @@ -33,8 +33,7 @@
>> >  static inline u32 __dcc_getstatus(void)
>> >  {
>> >  	u32 __ret;
>> > -
>> > -	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
>> > +	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
>> >  		: "=r" (__ret) : : "cc");
>> >  
>> >  	return __ret;
>
> Is volatile needed here? If __dcc_getstatus() return value is
> discarded, we want assembly discarded, right?

That's not really the issue being fixed.  Without the volatile, the
compiler is free to cache and reuse a previously loaded status value.
It is important that the status be read each time.

I don't think there is a way of indicating that assembly needs to happen
for each use, but that it is OK to discard if the value isn't used.
'volatile' is a bit overloaded.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2011-01-02 18:49                 ` David Brown
@ 2011-01-03  5:50                   ` Pavel Machek
  0 siblings, 0 replies; 39+ messages in thread
From: Pavel Machek @ 2011-01-03  5:50 UTC (permalink / raw)
  To: David Brown
  Cc: Nicolas Pitre, Stephen Boyd, Greg Kroah-Hartman, linux-kernel,
	linux-arm-msm, linux-arm-kernel, Tony Lindgren, Arnd Bergmann,
	Daniel Walker

On Sun 2011-01-02 10:49:32, David Brown wrote:
> On Sun, Jan 02 2011, Pavel Machek wrote:
> 
> >> > diff --git a/drivers/char/hvc_dcc.c b/drivers/char/hvc_dcc.c
> >> > index 6470f63..155ec10 100644
> >> > --- a/drivers/char/hvc_dcc.c
> >> > +++ b/drivers/char/hvc_dcc.c
> >> > @@ -33,8 +33,7 @@
> >> >  static inline u32 __dcc_getstatus(void)
> >> >  {
> >> >  	u32 __ret;
> >> > -
> >> > -	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
> >> > +	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
> >> >  		: "=r" (__ret) : : "cc");
> >> >  
> >> >  	return __ret;
> >
> > Is volatile needed here? If __dcc_getstatus() return value is
> > discarded, we want assembly discarded, right?
> 
> That's not really the issue being fixed.  Without the volatile, the
> compiler is free to cache and reuse a previously loaded status value.
> It is important that the status be read each time.
> 
> I don't think there is a way of indicating that assembly needs to happen
> for each use, but that it is OK to discard if the value isn't used.
> 'volatile' is a bit overloaded.

Ok, thanks for explanation.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2010-12-20 21:39             ` Nicolas Pitre
  2011-01-02  9:00               ` Pavel Machek
@ 2011-01-04 18:49               ` Tony Lindgren
  1 sibling, 0 replies; 39+ messages in thread
From: Tony Lindgren @ 2011-01-04 18:49 UTC (permalink / raw)
  To: Nicolas Pitre
  Cc: Stephen Boyd, Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Arnd Bergmann, Daniel Walker

* Nicolas Pitre <nico@fluxnic.net> [101220 13:38]:
> On Mon, 20 Dec 2010, Stephen Boyd wrote:
> 
> > Without marking the asm __dcc_getstatus() volatile my compiler
> > decides it can cache the value of __ret in a register and then
> > check the value of it continually in hvc_dcc_put_chars() (I had
> > to replace get_wait/put_wait with 1 and fixup the branch
> > otherwise my disassembler barfed on __dcc_(get|put)char).
> > 
> > 00000000 <hvc_dcc_put_chars>:
> >    0:   ee103e11        mrc     14, 0, r3, cr0, cr1, {0}
> >    4:   e3a0c000        mov     ip, #0  ; 0x0
> >    8:   e2033202        and     r3, r3, #536870912      ; 0x20000000
> >    c:   ea000006        b       2c <hvc_dcc_put_chars+0x2c>
> >   10:   e3530000        cmp     r3, #0  ; 0x0
> >   14:   1afffffd        bne     10 <hvc_dcc_put_chars+0x10>
> >   18:   e7d1000c        ldrb    r0, [r1, ip]
> >   1c:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
> >   20:   2afffffd        bcs     1c <hvc_dcc_put_chars+0x1c>
> >   24:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
> >   28:   e28cc001        add     ip, ip, #1      ; 0x1
> >   2c:   e15c0002        cmp     ip, r2
> >   30:   bafffff6        blt     10 <hvc_dcc_put_chars+0x10>
> >   34:   e1a00002        mov     r0, r2
> >   38:   e12fff1e        bx      lr
> > 
> > As you can see, the value of the mrc is checked against
> > DCC_STATUS_TX (bit 29) and then stored in r3 for later use.
> > Marking the asm volatile produces the following:
> > 
> > 00000000 <hvc_dcc_put_chars>:
> >    0:   e3a03000        mov     r3, #0  ; 0x0
> >    4:   ea000007        b       28 <hvc_dcc_put_chars+0x28>
> >    8:   ee100e11        mrc     14, 0, r0, cr0, cr1, {0}
> >    c:   e3100202        tst     r0, #536870912  ; 0x20000000
> >   10:   1afffffc        bne     8 <hvc_dcc_put_chars+0x8>
> >   14:   e7d10003        ldrb    r0, [r1, r3]
> >   18:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
> >   1c:   2afffffd        bcs     18 <hvc_dcc_put_chars+0x18>
> >   20:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
> >   24:   e2833001        add     r3, r3, #1      ; 0x1
> >   28:   e1530002        cmp     r3, r2
> >   2c:   bafffff5        blt     8 <hvc_dcc_put_chars+0x8>
> >   30:   e1a00002        mov     r0, r2
> >   34:   e12fff1e        bx      lr
> > 
> > which looks better and actually works. Mark all the inline
> > assembly in this file as volatile since we don't want the
> > compiler to optimize away these statements or move them around
> > in any way.
> > 
> > Cc: Tony Lindgren <tony@atomide.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
> > Cc: Daniel Walker <dwalker@codeaurora.org>
> > Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> 
> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

Acked-by: Tony Lindgren <tony@atomide.com>

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2010-12-20 21:44             ` Nicolas Pitre
@ 2011-01-04 18:52               ` Tony Lindgren
  0 siblings, 0 replies; 39+ messages in thread
From: Tony Lindgren @ 2011-01-04 18:52 UTC (permalink / raw)
  To: Nicolas Pitre
  Cc: Stephen Boyd, Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel, Arnd Bergmann, Daniel Walker

* Nicolas Pitre <nico@fluxnic.net> [101220 13:44]:
> On Mon, 20 Dec 2010, Stephen Boyd wrote:
> 
> > The inline assembly differences for v6 vs. v7 in the hvc_dcc
> > driver are purely optimizations. On a v7 processor, an mrc with
> > the pc sets the condition codes to the 28-31 bits of the register
> > being read. It just so happens that the TX/RX full bits the DCC
> > driver is testing for are high enough in the register to be put
> > into the condition codes. On a v6 processor, this "feature" isn't
> > implemented and thus we have to do the usual read, mask, test
> > operations to check for TX/RX full.
> > 
> > Since we already test the RX/TX full bits before calling
> > __dcc_getchar() and __dcc_putchar() we don't actually need to do
> > anything special for v7 over v6. The only difference is in
> > hvc_dcc_get_chars(). We would test RX full, poll RX full, and
> > then read a character from the buffer, whereas now we will test
> > RX full, read a character from the buffer, and then test RX full
> > again for the second iteration of the loop. It doesn't seem
> > possible for the buffer to go from full to empty between testing
> > the RX full and reading a character. Therefore, replace the v7
> > versions with the v6 versions and everything works the same.
> > 
> > Cc: Tony Lindgren <tony@atomide.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
> > Cc: Daniel Walker <dwalker@codeaurora.org>
> > Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> 
> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

Acked-by: Tony Lindgren <tony@atomide.com>

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 0/3] hvc_dcc cleanups and fixes
  2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
                             ` (2 preceding siblings ...)
  2010-12-20 20:08           ` [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
@ 2011-01-06  1:49           ` Stephen Boyd
  2011-01-06  3:20             ` Greg KH
  2011-02-03 22:17           ` Greg KH
  4 siblings, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2011-01-06  1:49 UTC (permalink / raw)
  To: Greg Kroah-Hartman; +Cc: linux-kernel, linux-arm-msm, linux-arm-kernel

Greg,

On 12/20/2010 12:08 PM, Stephen Boyd wrote:
> Here are the split patches.

Should I resend these with the proper acks or can/have you picked these
patches up?

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 0/3] hvc_dcc cleanups and fixes
  2011-01-06  1:49           ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
@ 2011-01-06  3:20             ` Greg KH
  0 siblings, 0 replies; 39+ messages in thread
From: Greg KH @ 2011-01-06  3:20 UTC (permalink / raw)
  To: Stephen Boyd; +Cc: linux-kernel, linux-arm-msm, linux-arm-kernel

On Wed, Jan 05, 2011 at 05:49:17PM -0800, Stephen Boyd wrote:
> Greg,
> 
> On 12/20/2010 12:08 PM, Stephen Boyd wrote:
> > Here are the split patches.
> 
> Should I resend these with the proper acks or can/have you picked these
> patches up?

They are in my to-apply queue after .38-rc1 is out.

thanks,

greg k-h

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-12-07 19:10       ` Stephen Boyd
@ 2011-01-14 19:19         ` Tony Lindgren
  2011-01-14 23:49           ` Stephen Boyd
  0 siblings, 1 reply; 39+ messages in thread
From: Tony Lindgren @ 2011-01-14 19:19 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Daniel Walker, linux-kernel, linux-arm-msm, Arnd Bergmann,
	Nicolas Pitre, Greg Kroah-Hartman, Mike Frysinger, Andrew Morton,
	Alan Cox, Randy Dunlap, FUJITA Tomonori, linuxppc-dev

* Stephen Boyd <sboyd@codeaurora.org> [101207 11:00]:
> On 12/01/2010 12:20 PM, Stephen Boyd wrote:
> > Definitely for TX since it seems like a redundant loop, but I agree RX
> > code has changed. Instead of
> >
> > If RX buffer full
> > Poll for RX buffer full
> > Read character from RX buffer
> >
> > we would have
> >
> > If RX buffer full
> > Read character from RX buffer
> >
> > which doesn't seem all that different assuming the RX buffer doesn't go
> > from full to empty between the If and Poll steps. Hopefully Tony knows more.
> >
> 
> Tony, any thoughts?

Sorry for the delay, looks like I'm only 1 month behind with email..
Sounds like it should work to me. I can try it out if you point me
to a patch.

Regards,

Tony

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2011-01-14 19:19         ` Tony Lindgren
@ 2011-01-14 23:49           ` Stephen Boyd
  0 siblings, 0 replies; 39+ messages in thread
From: Stephen Boyd @ 2011-01-14 23:49 UTC (permalink / raw)
  To: Tony Lindgren
  Cc: Daniel Walker, linux-kernel, linux-arm-msm, Arnd Bergmann,
	Nicolas Pitre, Greg Kroah-Hartman, Mike Frysinger, Andrew Morton,
	Alan Cox, Randy Dunlap, FUJITA Tomonori, linuxppc-dev

On 01/14/2011 11:19 AM, Tony Lindgren wrote:
> * Stephen Boyd <sboyd@codeaurora.org> [101207 11:00]:
>> On 12/01/2010 12:20 PM, Stephen Boyd wrote:
>>> Definitely for TX since it seems like a redundant loop, but I agree RX
>>> code has changed. Instead of
>>>
>>> If RX buffer full
>>> Poll for RX buffer full
>>> Read character from RX buffer
>>>
>>> we would have
>>>
>>> If RX buffer full
>>> Read character from RX buffer
>>>
>>> which doesn't seem all that different assuming the RX buffer doesn't go
>>> from full to empty between the If and Poll steps. Hopefully Tony knows more.
>>>
>>
>> Tony, any thoughts?
>
> Sorry for the delay, looks like I'm only 1 month behind with email..
> Sounds like it should work to me. I can try it out if you point me
> to a patch.

I think you acked the patches to make this change. You can test them out
by applying the "hvc_dcc cleanups and fixes" patches (Message-Id:
<1292875718-7980-1-git-send-email-sboyd@codeaurora.org>) on top of this
patch. They were sent as a reply to this thread.

Stephen

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 0/3] hvc_dcc cleanups and fixes
  2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
                             ` (3 preceding siblings ...)
  2011-01-06  1:49           ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
@ 2011-02-03 22:17           ` Greg KH
  2011-02-03 23:19             ` Stephen Boyd
  2011-02-03 23:48             ` [PATCHv2 " Stephen Boyd
  4 siblings, 2 replies; 39+ messages in thread
From: Greg KH @ 2011-02-03 22:17 UTC (permalink / raw)
  To: Stephen Boyd
  Cc: Greg Kroah-Hartman, linux-kernel, linux-arm-msm, linux-arm-kernel

On Mon, Dec 20, 2010 at 12:08:35PM -0800, Stephen Boyd wrote:
> Here are the split patches.
> 
> The first two patches cleanup and fix the hvc_dcc driver for my
> compiler. The final patch is more controversial, it removes the
> v6 and v7 differences in this driver.
> 
> Stephen Boyd (3):
>   hvc_dcc: Fix bad code generation by marking assembly volatile
>   hvc_dcc: Simplify put_chars()/get_chars() loops
>   hvc_dcc: Simplify assembly for v6 and v7 ARM

Can you redo these against the linux-next tree as they don't apply
anymore and resend them so I can apply them?

thanks,

greg k-h

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 0/3] hvc_dcc cleanups and fixes
  2011-02-03 22:17           ` Greg KH
@ 2011-02-03 23:19             ` Stephen Boyd
  2011-02-03 23:30               ` Greg KH
  2011-02-03 23:48             ` [PATCHv2 " Stephen Boyd
  1 sibling, 1 reply; 39+ messages in thread
From: Stephen Boyd @ 2011-02-03 23:19 UTC (permalink / raw)
  To: Greg KH
  Cc: Stephen Boyd, Greg Kroah-Hartman, linux-kernel, linux-arm-msm,
	linux-arm-kernel

> On Mon, Dec 20, 2010 at 12:08:35PM -0800, Stephen Boyd wrote:
>> Here are the split patches.
>>
>> The first two patches cleanup and fix the hvc_dcc driver for my
>> compiler. The final patch is more controversial, it removes the
>> v6 and v7 differences in this driver.
>>
>> Stephen Boyd (3):
>>   hvc_dcc: Fix bad code generation by marking assembly volatile
>>   hvc_dcc: Simplify put_chars()/get_chars() loops
>>   hvc_dcc: Simplify assembly for v6 and v7 ARM
> 
> Can you redo these against the linux-next tree as they don't apply
> anymore and resend them so I can apply them?
> 

Have you tried 'git am -3' on them? I assume it's the movement of the
file that's causing the problem.

Either way, I'll resend and collect the acks in a bit.

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH 0/3] hvc_dcc cleanups and fixes
  2011-02-03 23:19             ` Stephen Boyd
@ 2011-02-03 23:30               ` Greg KH
  0 siblings, 0 replies; 39+ messages in thread
From: Greg KH @ 2011-02-03 23:30 UTC (permalink / raw)
  To: Stephen Boyd; +Cc: Greg KH, linux-kernel, linux-arm-msm, linux-arm-kernel

On Thu, Feb 03, 2011 at 03:19:07PM -0800, Stephen Boyd wrote:
> > On Mon, Dec 20, 2010 at 12:08:35PM -0800, Stephen Boyd wrote:
> >> Here are the split patches.
> >>
> >> The first two patches cleanup and fix the hvc_dcc driver for my
> >> compiler. The final patch is more controversial, it removes the
> >> v6 and v7 differences in this driver.
> >>
> >> Stephen Boyd (3):
> >>   hvc_dcc: Fix bad code generation by marking assembly volatile
> >>   hvc_dcc: Simplify put_chars()/get_chars() loops
> >>   hvc_dcc: Simplify assembly for v6 and v7 ARM
> > 
> > Can you redo these against the linux-next tree as they don't apply
> > anymore and resend them so I can apply them?
> > 
> 
> Have you tried 'git am -3' on them? I assume it's the movement of the
> file that's causing the problem.
> 
> Either way, I'll resend and collect the acks in a bit.

thanks, that would be great.

greg k-h


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCHv2 0/3] hvc_dcc cleanups and fixes
  2011-02-03 22:17           ` Greg KH
  2011-02-03 23:19             ` Stephen Boyd
@ 2011-02-03 23:48             ` Stephen Boyd
  2011-02-03 23:48               ` [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
                                 ` (2 more replies)
  1 sibling, 3 replies; 39+ messages in thread
From: Stephen Boyd @ 2011-02-03 23:48 UTC (permalink / raw)
  To: Greg KH; +Cc: linux-kernel, linux-arm-msm, linux-arm-kernel

Redone against tty-next and collected acks from Nicolas and Tony.

Stephen Boyd (3):
  hvc_dcc: Fix bad code generation by marking assembly volatile
  hvc_dcc: Simplify put_chars()/get_chars() loops
  hvc_dcc: Simplify assembly for v6 and v7 ARM

 drivers/tty/hvc/hvc_dcc.c |   43 +++++++------------------------------------
 1 files changed, 7 insertions(+), 36 deletions(-)

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile
  2011-02-03 23:48             ` [PATCHv2 " Stephen Boyd
@ 2011-02-03 23:48               ` Stephen Boyd
  2011-02-03 23:48               ` [PATCHv2 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
  2011-02-03 23:48               ` [PATCHv2 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
  2 siblings, 0 replies; 39+ messages in thread
From: Stephen Boyd @ 2011-02-03 23:48 UTC (permalink / raw)
  To: Greg KH
  Cc: linux-kernel, linux-arm-msm, linux-arm-kernel, Arnd Bergmann,
	Daniel Walker

Without marking the asm __dcc_getstatus() volatile my compiler
decides it can cache the value of __ret in a register and then
check the value of it continually in hvc_dcc_put_chars() (I had
to replace get_wait/put_wait with 1 and fixup the branch
otherwise my disassembler barfed on __dcc_(get|put)char).

00000000 <hvc_dcc_put_chars>:
   0:   ee103e11        mrc     14, 0, r3, cr0, cr1, {0}
   4:   e3a0c000        mov     ip, #0  ; 0x0
   8:   e2033202        and     r3, r3, #536870912      ; 0x20000000
   c:   ea000006        b       2c <hvc_dcc_put_chars+0x2c>
  10:   e3530000        cmp     r3, #0  ; 0x0
  14:   1afffffd        bne     10 <hvc_dcc_put_chars+0x10>
  18:   e7d1000c        ldrb    r0, [r1, ip]
  1c:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  20:   2afffffd        bcs     1c <hvc_dcc_put_chars+0x1c>
  24:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  28:   e28cc001        add     ip, ip, #1      ; 0x1
  2c:   e15c0002        cmp     ip, r2
  30:   bafffff6        blt     10 <hvc_dcc_put_chars+0x10>
  34:   e1a00002        mov     r0, r2
  38:   e12fff1e        bx      lr

As you can see, the value of the mrc is checked against
DCC_STATUS_TX (bit 29) and then stored in r3 for later use.
Marking the asm volatile produces the following:

00000000 <hvc_dcc_put_chars>:
   0:   e3a03000        mov     r3, #0  ; 0x0
   4:   ea000007        b       28 <hvc_dcc_put_chars+0x28>
   8:   ee100e11        mrc     14, 0, r0, cr0, cr1, {0}
   c:   e3100202        tst     r0, #536870912  ; 0x20000000
  10:   1afffffc        bne     8 <hvc_dcc_put_chars+0x8>
  14:   e7d10003        ldrb    r0, [r1, r3]
  18:   ee10fe11        mrc     14, 0, pc, cr0, cr1, {0}
  1c:   2afffffd        bcs     18 <hvc_dcc_put_chars+0x18>
  20:   ee000e15        mcr     14, 0, r0, cr0, cr5, {0}
  24:   e2833001        add     r3, r3, #1      ; 0x1
  28:   e1530002        cmp     r3, r2
  2c:   bafffff5        blt     8 <hvc_dcc_put_chars+0x8>
  30:   e1a00002        mov     r0, r2
  34:   e12fff1e        bx      lr

which looks better and actually works. Mark all the inline
assembly in this file as volatile since we don't want the
compiler to optimize away these statements or move them around
in any way.

Acked-by: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/tty/hvc/hvc_dcc.c |   11 +++++------
 1 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
index 6470f63..155ec10 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c
@@ -33,8 +33,7 @@
 static inline u32 __dcc_getstatus(void)
 {
 	u32 __ret;
-
-	asm("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
+	asm volatile("mrc p14, 0, %0, c0, c1, 0	@ read comms ctrl reg"
 		: "=r" (__ret) : : "cc");
 
 	return __ret;
@@ -46,7 +45,7 @@ static inline char __dcc_getchar(void)
 {
 	char __c;
 
-	asm("get_wait:	mrc p14, 0, pc, c0, c1, 0                          \n\
+	asm volatile("get_wait:	mrc p14, 0, pc, c0, c1, 0                  \n\
 			bne get_wait                                       \n\
 			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
 		: "=r" (__c) : : "cc");
@@ -58,7 +57,7 @@ static inline char __dcc_getchar(void)
 {
 	char __c;
 
-	asm("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
+	asm volatile("mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
 		: "=r" (__c));
 
 	return __c;
@@ -68,7 +67,7 @@ static inline char __dcc_getchar(void)
 #if defined(CONFIG_CPU_V7)
 static inline void __dcc_putchar(char c)
 {
-	asm("put_wait:	mrc p14, 0, pc, c0, c1, 0                 \n\
+	asm volatile("put_wait:	mrc p14, 0, pc, c0, c1, 0         \n\
 			bcs put_wait                              \n\
 			mcr p14, 0, %0, c0, c5, 0                   "
 	: : "r" (c) : "cc");
@@ -76,7 +75,7 @@ static inline void __dcc_putchar(char c)
 #else
 static inline void __dcc_putchar(char c)
 {
-	asm("mcr p14, 0, %0, c0, c5, 0	@ write a char"
+	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
 		: /* no output register */
 		: "r" (c));
 }
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCHv2 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops
  2011-02-03 23:48             ` [PATCHv2 " Stephen Boyd
  2011-02-03 23:48               ` [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
@ 2011-02-03 23:48               ` Stephen Boyd
  2011-02-03 23:48               ` [PATCHv2 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
  2 siblings, 0 replies; 39+ messages in thread
From: Stephen Boyd @ 2011-02-03 23:48 UTC (permalink / raw)
  To: Greg KH; +Cc: linux-kernel, linux-arm-msm, linux-arm-kernel, Daniel Walker

Casting and anding with 0xff is unnecessary in
hvc_dcc_put_chars() since buf is already a char[].
__dcc_get_char() can't return an int less than 0 since it only
returns a char. Simplify the if statement in hvc_dcc_get_chars()
to take this into account.

Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/tty/hvc/hvc_dcc.c |   12 ++++--------
 1 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
index 155ec10..ad23cc8 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c
@@ -89,7 +89,7 @@ static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
 		while (__dcc_getstatus() & DCC_STATUS_TX)
 			cpu_relax();
 
-		__dcc_putchar((char)(buf[i] & 0xFF));
+		__dcc_putchar(buf[i]);
 	}
 
 	return count;
@@ -99,15 +99,11 @@ static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
 {
 	int i;
 
-	for (i = 0; i < count; ++i) {
-		int c = -1;
-
+	for (i = 0; i < count; ++i)
 		if (__dcc_getstatus() & DCC_STATUS_RX)
-			c = __dcc_getchar();
-		if (c < 0)
+			buf[i] = __dcc_getchar();
+		else
 			break;
-		buf[i] = c;
-	}
 
 	return i;
 }
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* [PATCHv2 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM
  2011-02-03 23:48             ` [PATCHv2 " Stephen Boyd
  2011-02-03 23:48               ` [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
  2011-02-03 23:48               ` [PATCHv2 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
@ 2011-02-03 23:48               ` Stephen Boyd
  2 siblings, 0 replies; 39+ messages in thread
From: Stephen Boyd @ 2011-02-03 23:48 UTC (permalink / raw)
  To: Greg KH
  Cc: linux-kernel, linux-arm-msm, linux-arm-kernel, Arnd Bergmann,
	Daniel Walker

The inline assembly differences for v6 vs. v7 in the hvc_dcc
driver are purely optimizations. On a v7 processor, an mrc with
the pc sets the condition codes to the 28-31 bits of the register
being read. It just so happens that the TX/RX full bits the DCC
driver is testing for are high enough in the register to be put
into the condition codes. On a v6 processor, this "feature" isn't
implemented and thus we have to do the usual read, mask, test
operations to check for TX/RX full.

Since we already test the RX/TX full bits before calling
__dcc_getchar() and __dcc_putchar() we don't actually need to do
anything special for v7 over v6. The only difference is in
hvc_dcc_get_chars(). We would test RX full, poll RX full, and
then read a character from the buffer, whereas now we will test
RX full, read a character from the buffer, and then test RX full
again for the second iteration of the loop. It doesn't seem
possible for the buffer to go from full to empty between testing
the RX full and reading a character. Therefore, replace the v7
versions with the v6 versions and everything works the same.

Acked-by: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/tty/hvc/hvc_dcc.c |   24 ------------------------
 1 files changed, 0 insertions(+), 24 deletions(-)

diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
index ad23cc8..435f6fa 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c
@@ -40,19 +40,6 @@ static inline u32 __dcc_getstatus(void)
 }
 
 
-#if defined(CONFIG_CPU_V7)
-static inline char __dcc_getchar(void)
-{
-	char __c;
-
-	asm volatile("get_wait:	mrc p14, 0, pc, c0, c1, 0                  \n\
-			bne get_wait                                       \n\
-			mrc p14, 0, %0, c0, c5, 0	@ read comms data reg"
-		: "=r" (__c) : : "cc");
-
-	return __c;
-}
-#else
 static inline char __dcc_getchar(void)
 {
 	char __c;
@@ -62,24 +49,13 @@ static inline char __dcc_getchar(void)
 
 	return __c;
 }
-#endif
 
-#if defined(CONFIG_CPU_V7)
-static inline void __dcc_putchar(char c)
-{
-	asm volatile("put_wait:	mrc p14, 0, pc, c0, c1, 0         \n\
-			bcs put_wait                              \n\
-			mcr p14, 0, %0, c0, c5, 0                   "
-	: : "r" (c) : "cc");
-}
-#else
 static inline void __dcc_putchar(char c)
 {
 	asm volatile("mcr p14, 0, %0, c0, c5, 0	@ write a char"
 		: /* no output register */
 		: "r" (c));
 }
-#endif
 
 static int hvc_dcc_put_chars(uint32_t vt, const char *buf, int count)
 {
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2010-11-30 19:25 [PATCH] drivers: char: hvc: add arm JTAG DCC console support Daniel Walker
  2010-11-30 19:57 ` Nicolas Pitre
  2010-12-01  5:30 ` Stephen Boyd
@ 2011-04-07 18:39 ` RONETIX - Asen Dimov
  2011-04-07 18:57   ` Mike Frysinger
  2 siblings, 1 reply; 39+ messages in thread
From: RONETIX - Asen Dimov @ 2011-04-07 18:39 UTC (permalink / raw)
  To: Daniel Walker
  Cc: linux-kernel, Randy Dunlap, Mike Frysinger, Arnd Bergmann,
	Nicolas Pitre, Tony Lindgren, linux-arm-msm, Greg Kroah-Hartman,
	FUJITA Tomonori, Andrew Morton, linuxppc-dev, Alan Cox

Hello,

On 11/30/2010 09:25 PM, Daniel Walker wrote:
> This driver adds a basic console that uses the arm JTAG
> DCC to transfer data back and forth. It has support for
> ARMv6 and ARMv7.
>
> This console is created under the HVC driver, and should be named
> /dev/hvcX (or /dev/hvc0 for example).
>
> Cc: Tony Lindgren<tony@atomide.com>
> Cc: Arnd Bergmann<arnd@arndb.de>
> Cc: Nicolas Pitre<nico@fluxnic.net>
> Cc: Greg Kroah-Hartman<gregkh@suse.de>
> Cc: Mike Frysinger<vapier@gentoo.org>
> Signed-off-by: Daniel Walker<dwalker@codeaurora.org>
> ---
>   drivers/char/Kconfig   |    9 +++
>   drivers/char/Makefile  |    1 +
>   drivers/char/hvc_dcc.c |  133 ++++++++++++++++++++++++++++++++++++++++++++++++
...

this DCC driver implements "one channel", but what about implementing
"multiple channels". For example reserve few(3) bits for channel number,
and two bits for carried data, then fill the rest bytes with with some data
and send the word(32 bits) over DCC. On the Linux side writing on /dev/hvcX
puts the number X as channel number, and on the other side the CPU
emulator gets the data and redistribute it to TCP/IP socket.

I have started write some code implementing this. Are there any one 
interested
in this multiple channels, and are there any one started to work on it?


Regards,
Asen

^ permalink raw reply	[flat|nested] 39+ messages in thread

* Re: [PATCH] drivers: char: hvc: add arm JTAG DCC console support
  2011-04-07 18:39 ` RONETIX - Asen Dimov
@ 2011-04-07 18:57   ` Mike Frysinger
  0 siblings, 0 replies; 39+ messages in thread
From: Mike Frysinger @ 2011-04-07 18:57 UTC (permalink / raw)
  To: RONETIX - Asen Dimov
  Cc: Daniel Walker, linux-kernel, Randy Dunlap, Arnd Bergmann,
	Nicolas Pitre, Tony Lindgren, linux-arm-msm, Greg Kroah-Hartman,
	FUJITA Tomonori, Andrew Morton, linuxppc-dev, Alan Cox

On Thu, Apr 7, 2011 at 14:39, RONETIX - Asen Dimov wrote:
> On 11/30/2010 09:25 PM, Daniel Walker wrote:
>> This driver adds a basic console that uses the arm JTAG
>> DCC to transfer data back and forth. It has support for
>> ARMv6 and ARMv7.
>>
>> This console is created under the HVC driver, and should be named
>> /dev/hvcX (or /dev/hvc0 for example).
>>
>>  drivers/char/Kconfig   |    9 +++
>>  drivers/char/Makefile  |    1 +
>>  drivers/char/hvc_dcc.c |  133
>> ++++++++++++++++++++++++++++++++++++++++++++++++
>
> ...
>
> this DCC driver implements "one channel", but what about implementing
> "multiple channels". For example reserve few(3) bits for channel number,
> and two bits for carried data, then fill the rest bytes with with some data
> and send the word(32 bits) over DCC. On the Linux side writing on /dev/hvcX
> puts the number X as channel number, and on the other side the CPU
> emulator gets the data and redistribute it to TCP/IP socket.
>
> I have started write some code implementing this. Are there any one
> interested
> in this multiple channels, and are there any one started to work on it?

this sort of multiplexing of the data stream sounds like the job for
userspace ?  or maybe a line discipline ?  inserting structured data
into the kernel driver doesnt sound right to me ...
-mike

^ permalink raw reply	[flat|nested] 39+ messages in thread

end of thread, other threads:[~2011-04-07 18:58 UTC | newest]

Thread overview: 39+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2010-11-30 19:25 [PATCH] drivers: char: hvc: add arm JTAG DCC console support Daniel Walker
2010-11-30 19:57 ` Nicolas Pitre
2010-11-30 21:17   ` Arnd Bergmann
2010-12-01  5:30 ` Stephen Boyd
2010-12-01 18:54   ` Daniel Walker
2010-12-01 19:28     ` Greg KH
2010-12-18  5:16       ` [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
2010-12-20 17:51         ` Daniel Walker
2010-12-20 18:39           ` Stephen Boyd
2010-12-20 18:46             ` Nicolas Pitre
2010-12-20 20:08         ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
2010-12-20 20:08           ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
2010-12-20 21:39             ` Nicolas Pitre
2011-01-02  9:00               ` Pavel Machek
2011-01-02 18:49                 ` David Brown
2011-01-03  5:50                   ` Pavel Machek
2011-01-04 18:49               ` Tony Lindgren
2010-12-20 21:49             ` Arnaud Lacombe
2010-12-20 21:52               ` Stephen Boyd
2010-12-20 22:10                 ` Nicolas Pitre
2010-12-20 20:08           ` [PATCH 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
2010-12-20 20:08           ` [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
2010-12-20 21:44             ` Nicolas Pitre
2011-01-04 18:52               ` Tony Lindgren
2011-01-06  1:49           ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd
2011-01-06  3:20             ` Greg KH
2011-02-03 22:17           ` Greg KH
2011-02-03 23:19             ` Stephen Boyd
2011-02-03 23:30               ` Greg KH
2011-02-03 23:48             ` [PATCHv2 " Stephen Boyd
2011-02-03 23:48               ` [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd
2011-02-03 23:48               ` [PATCHv2 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd
2011-02-03 23:48               ` [PATCHv2 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd
2010-12-01 20:20     ` [PATCH] drivers: char: hvc: add arm JTAG DCC console support Stephen Boyd
2010-12-07 19:10       ` Stephen Boyd
2011-01-14 19:19         ` Tony Lindgren
2011-01-14 23:49           ` Stephen Boyd
2011-04-07 18:39 ` RONETIX - Asen Dimov
2011-04-07 18:57   ` Mike Frysinger

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