Re: [PATCH 3/5] ARC: handle DSP presence in HW

[Vineet Gupta <Vineet.Gupta1@synopsys.com>]

On 12/27/19 10:03 AM, Eugeniy Paltsev wrote:
> In case of DSP extension presence in HW some instructions
> (related to integer multiply, multiply-accumulate, and divide
> operation) executes on this DSP execution unit. So their
> execution will depend on dsp configuration register (DSP_CTRL)
>
> As we want these instructions to execute the same way regardless
> of DSP presence we need to set DSP_CTRL properly. However this
> register can be modified bu any usersace app therefore any
> usersace may break kernel execution.
>
> Fix that by configure DSP_CTRL in CPU early code and in IRQs
> entries.
>
> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> ---
>  arch/arc/Kconfig                   | 25 ++++++++++++++++-
>  arch/arc/include/asm/arcregs.h     | 12 ++++++++
>  arch/arc/include/asm/dsp-impl.h    | 45 ++++++++++++++++++++++++++++++
>  arch/arc/include/asm/entry-arcv2.h |  3 ++
>  arch/arc/kernel/head.S             |  4 +++
>  arch/arc/kernel/setup.c            |  4 +++
>  6 files changed, 92 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arc/include/asm/dsp-impl.h
>
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index 8383155c8c82..b9cd7ce3f878 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -404,13 +404,36 @@ config ARC_HAS_DIV_REM
>  	default y
>  
>  config ARC_HAS_ACCL_REGS
> -	bool "Reg Pair ACCL:ACCH (FPU and/or MPY > 6)"
> +	bool "Reg Pair ACCL:ACCH (FPU and/or MPY > 6 and/or DSP)"
>  	default y
>  	help
>  	  Depending on the configuration, CPU can contain accumulator reg-pair
>  	  (also referred to as r58:r59). These can also be used by gcc as GPR so
>  	  kernel needs to save/restore per process
>  
> +choice
> +	prompt "DSP support"
> +	default ARC_NO_DSP
> +	help
> +	  Depending on the configuration, CPU can contain DSP registers
> +	  (ACC0_GLO, ACC0_GHI, DSP_BFLY0, DSP_CTRL, DSP_FFT_CTRL).
> +	  Bellow is options describing how to handle these registers in
> +	  interrupt entry / exit and in context switch.
> +
> +config ARC_NO_DSP

Can this be called ARC_DSP_NONE for better intuitive regex searches !

> +	bool "No DSP extension presence in HW"
> +	help
> +	  No DSP extension presence in HW
> +
> +config ARC_DSP_KERNEL
> +	bool "DSP extension in HW, no support for userspace"
> +	select ARC_HAS_ACCL_REGS
> +	help
> +	  DSP extension presence in HW, no support for DSP-enabled userspace
> +	  applications. We don't save / restore DSP registers and only do
> +	  some minimal preparations so userspace won't be able to break kernel
> +endchoice
> +
>  config ARC_IRQ_NO_AUTOSAVE
>  	bool "Disable hardware autosave regfile on interrupts"
>  	default n
> diff --git a/arch/arc/include/asm/arcregs.h b/arch/arc/include/asm/arcregs.h
> index 5134f0baf33c..0004b1e9b325 100644
> --- a/arch/arc/include/asm/arcregs.h
> +++ b/arch/arc/include/asm/arcregs.h
> @@ -116,6 +116,18 @@
>  #define ARC_AUX_DPFP_2H         0x304
>  #define ARC_AUX_DPFP_STAT       0x305
>  
> +/*
> + * DSP-related registers
> + */
> +#define ARC_AUX_DSP_BUILD	0x7A
> +#define ARC_AUX_ACC0_LO		0x580
> +#define ARC_AUX_ACC0_GLO	0x581
> +#define ARC_AUX_ACC0_HI		0x582
> +#define ARC_AUX_ACC0_GHI	0x583
> +#define ARC_AUX_DSP_BFLY0	0x598
> +#define ARC_AUX_DSP_CTRL	0x59F
> +#define ARC_AUX_DSP_FFT_CTRL	0x59E
> +
>  #ifndef __ASSEMBLY__
>  
>  #include <soc/arc/aux.h>
> diff --git a/arch/arc/include/asm/dsp-impl.h b/arch/arc/include/asm/dsp-impl.h
> new file mode 100644
> index 000000000000..788093cbe689
> --- /dev/null
> +++ b/arch/arc/include/asm/dsp-impl.h
> @@ -0,0 +1,45 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2020 Synopsys, Inc. (www.synopsys.com)
> + *
> + * Author: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> + */
> +#ifndef __ASM_ARC_DSP_IMPL_H
> +#define __ASM_ARC_DSP_IMPL_H
> +
> +#define DSP_CTRL_DISABLED_ALL		0
> +
> +#ifdef __ASSEMBLY__
> +
> +/* clobbers r5 register */
> +.macro DSP_EARLY_INIT
> +	lr	r5, [ARC_AUX_DSP_BUILD]
> +	bmsk	r5, r5, 7
> +	breq    r5, 0, 1f
> +	mov	r5, DSP_CTRL_DISABLED_ALL
> +	sr	r5, [ARC_AUX_DSP_CTRL]
> +1:
> +.endm
> +
> +/* clobbers r58, r59 registers pair */
> +.macro DSP_SAVE_REGFILE_IRQ
> +#if defined(CONFIG_ARC_DSP_KERNEL)
> +	/* Drop any changes to DSP_CTRL made by userspace so userspace won't be
> +	 * able to break kernel */
> +	mov	r58, DSP_CTRL_DISABLED_ALL
> +	sr	r58, [ARC_AUX_DSP_CTRL]

In low level entry code, we typically use r10/r11 for scratch purposes, can u use
r10 here for consistency !

> +#endif /* ARC_DSP_KERNEL */
> +.endm
> +
> +#else /* __ASEMBLY__ */
> +
> +static inline bool dsp_exist(void)
> +{
> +	struct bcr_generic bcr;
> +
> +	READ_BCR(ARC_AUX_DSP_BUILD, bcr);
> +	return !!bcr.ver;

open code these use once / one liners in the call site itself.

> +}
> +
> +#endif /* __ASEMBLY__ */
> +#endif /* __ASM_ARC_DSP_IMPL_H */
> diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
> index 0b8b63d0bec1..e3f8bd3e2eba 100644
> --- a/arch/arc/include/asm/entry-arcv2.h
> +++ b/arch/arc/include/asm/entry-arcv2.h
> @@ -4,6 +4,7 @@
>  #define __ASM_ARC_ENTRY_ARCV2_H
>  
>  #include <asm/asm-offsets.h>
> +#include <asm/dsp-impl.h>
>  #include <asm/irqflags-arcv2.h>
>  #include <asm/thread_info.h>	/* For THREAD_SIZE */
>  
> @@ -165,6 +166,8 @@
>  	ST2	r58, r59, PT_r58
>  #endif
>  
> +	/* clobbers r58, r59 registers pair, so must be after r58, r59 save */
> +	DSP_SAVE_REGFILE_IRQ
>  .endm
>  
>  /*------------------------------------------------------------------------*/
> diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
> index 6f41265f6250..6eb23f1545ee 100644
> --- a/arch/arc/kernel/head.S
> +++ b/arch/arc/kernel/head.S
> @@ -14,6 +14,7 @@
>  #include <asm/entry.h>
>  #include <asm/arcregs.h>
>  #include <asm/cache.h>
> +#include <asm/dsp-impl.h>
>  #include <asm/irqflags.h>
>  
>  .macro CPU_EARLY_SETUP
> @@ -59,6 +60,9 @@
>  #endif
>  	kflag	r5
>  #endif
> +	; Config DSP_CTRL properly, so kernel may use integer multiply,
> +	; multiply-accumulate, and divide operations



> +	DSP_EARLY_INIT
>  .endm
>  
>  	.section .init.text, "ax",@progbits
> diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
> index edb55b6ee278..b3995dd673d9 100644
> --- a/arch/arc/kernel/setup.c
> +++ b/arch/arc/kernel/setup.c
> @@ -26,6 +26,7 @@
>  #include <asm/unwind.h>
>  #include <asm/mach_desc.h>
>  #include <asm/smp.h>
> +#include <asm/dsp-impl.h>
>  
>  #define FIX_PTR(x)  __asm__ __volatile__(";" : "+r"(x))
>  
> @@ -444,6 +445,9 @@ static void arc_chk_core_config(void)
>  		/* Accumulator Low:High pair (r58:59) present if DSP MPY or FPU */
>  		present = cpu->extn_mpy.dsp | cpu->extn.fpu_sp | cpu->extn.fpu_dp;
>  		CHK_OPT_STRICT(CONFIG_ARC_HAS_ACCL_REGS, present);
> +
> +		present = dsp_exist();

Open code as suggested above.

> +		CHK_OPT_STRICT(CONFIG_ARC_DSP_KERNEL, present);
>  	}
>  }
>