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From: "McKay, Luke" <Luke.McKay@aeroflex.com>
To: Andrey Utkin <andrey.krieger.utkin@gmail.com>,
	Stephen Hemminger <stephen@networkplumber.org>
Cc: "kernel-mentors@selenic.com" <kernel-mentors@selenic.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: RE: Question on MSI support in PCI and PCI-E devices
Date: Mon, 2 Mar 2015 14:02:33 +0000	[thread overview]
Message-ID: <41F544F51A709A4AA2914581E1219BDCBE480B@SEC-MBX-01.aeroflex.corp> (raw)
In-Reply-To: <CANZNk80AM6kuouG6dMsBMS1=YnM3OhcP2YHM5xTZRSsUpKg+Dw@mail.gmail.com>

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It doesn't appear that your device supports MSI.  If it did lspci -v should list the MSI capability and whether or not it is enabled.

i.e. Something like...
Capabilities: [68] MSI: Enable+ Count=1/1 Maskable- 64bit+

Without a listing that shows the capability is present, there is nothing to enable.

Have you tried polling instead of using interrupts?  Definitely not ideal, but it might help you to determine whether hardware is dropping/missing an interrupt or whether the hardware is being completely hung up.  

Do you know if this missing interrupt is occurring in other systems as well?  How about whether it happens with different boards in the same system?  Answers to these questions would help to determine whether you might have a defective board, or some sort of incompatibility with the system.

Regards,
Luke


-- 
Luke McKay 
Senior Engineer
Cobham AvComm
T : +1 (316) 529 5585

Please consider the environment before printing this email


-----Original Message-----
From: Kernel-mentors [mailto:kernel-mentors-bounces@selenic.com] On Behalf Of Andrey Utkin
Sent: Thursday, February 12, 2015 9:12 AM
To: Stephen Hemminger
Cc: kernel-mentors@selenic.com; linux-kernel@vger.kernel.org; kernelnewbies
Subject: Re: Question on MSI support in PCI and PCI-E devices

2015-02-12 16:48 GMT+02:00 Stephen Hemminger <stephen@networkplumber.org>:
> On Wed, 11 Feb 2015 18:19:00 +0000
> Andrey Utkin <andrey.krieger.utkin@gmail.com> wrote:
>
>> Is it true that _every_ PCI or PCI Express device supporting MSI is 
>> indicated by some mention of MSI in "lspci -v", and if there's no 
>> such mention, it surely doesn't support MSI?
>>
>
> Look at kernel source (drivers/pci/msi.c) function pci_msi_supported 
> there are many things which can block MSI.
>
> There can be cases where PCI quirks in kernel block MSI because for 
> example the device supports MSI, but the motherboard BIOS is broken. 
> This only happens on really old systems.

Thank you for your reply.
However, I was more interested in the case when lspci for device doesn't mention MSI at all, so I wonder if it makes sense to try to enable it in the driver at all.

04:05.0 Multimedia video controller: Bluecherry BC-H16480A 16 port
H.264 video and audio encoder / decoder
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV+ VGASnoop-
ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap- 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium
>TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 64 (250ns max), Cache Line Size: 32 bytes
        Interrupt: pin A routed to IRQ 16
        Region 0: Memory at faff0000 (32-bit, prefetchable) [size=64K]
        Kernel driver in use: solo6x10

We have such cards, and we have issues with them - at some moment they stop producing interrupts. No matter whether they share interrupt number or not.
There was a recent commit from Krzysztof Hałasa
(3c787b108fe0d1c341a76e718a25897ae14673cf) which improved things, but the issue still happens regularly on some setups.
Now I've tried the following change, i've introduced such a loop which I see in bt8xx and ddbridge drivers. This also didn't help. So I'm out of ideas now (any comments are highly appreciated!); I have read about MSI, that this interrupts transmission mechanism is more reliable and fast, but from lspci output it is not clear whether our cards support MSI at all.

--- a/drivers/media/pci/solo6x10/solo6x10-core.c
+++ b/drivers/media/pci/solo6x10/solo6x10-core.c
@@ -100,10 +100,13 @@ static irqreturn_t solo_isr(int irq, void *data)
        struct solo_dev *solo_dev = data;
        u32 status;
        int i;
+       int handled = 0;

+       while (1) {
        status = solo_reg_read(solo_dev, SOLO_IRQ_STAT);
        if (!status)
-               return IRQ_NONE;
+               break;
+       handled++;

        /* Acknowledge all interrupts immediately */
        solo_reg_write(solo_dev, SOLO_IRQ_STAT, status); @@ -129,7 +132,11 @@ static irqreturn_t solo_isr(int irq, void *data)
        if (status & SOLO_IRQ_G723)
                solo_g723_isr(solo_dev);

-       return IRQ_HANDLED;
+       }
+
+       if (handled > 1)
+               solo_dev->isr_more_laps++;
+       return IRQ_RETVAL(handled);
 }

 static void free_solo_dev(struct solo_dev *solo_dev) @@ -232,6 +239,16 @@ static ssize_t p2m_timeouts_show(struct device *dev,
        return sprintf(buf, "%d\n", solo_dev->p2m_timeouts);  }

+static ssize_t isr_more_laps_show(struct device *dev,
+                                 struct device_attribute *attr,
+                                 char *buf) {
+       struct solo_dev *solo_dev =
+               container_of(dev, struct solo_dev, dev);
+
+       return sprintf(buf, "%d\n", solo_dev->isr_more_laps); }
+
 static ssize_t sdram_size_show(struct device *dev,
                               struct device_attribute *attr,
                               char *buf) @@ -415,6 +432,7 @@ static const struct device_attribute solo_dev_attrs[] = {
        __ATTR_RO(input_map),
        __ATTR_RO(intervals),
        __ATTR_RO(sdram_offsets),
+       __ATTR_RO(isr_more_laps),
 };

 static void solo_device_release(struct device *dev) index d19c0ae..dffd7d7
--- a/drivers/media/pci/solo6x10/solo6x10-enc.c
+++ b/drivers/media/pci/solo6x10/solo6x10-enc.c
@@ -28,7 +28,7 @@
 #define VI_PROG_HSIZE                  (1280 - 16)
 #define VI_PROG_VSIZE                  (1024 - 16)

-#define IRQ_LEVEL                      2
+#define IRQ_LEVEL                      3

 static void solo_capture_config(struct solo_dev *solo_dev)  { index 6c9bc70..4799ea2
--- a/drivers/media/pci/solo6x10/solo6x10.h
+++ b/drivers/media/pci/solo6x10/solo6x10.h
@@ -277,6 +277,8 @@ struct solo_dev {
        spinlock_t              slock;
        int                     old_write;
        struct list_head        vidq_active;
+
+       int                     isr_more_laps;
 };

 static inline u32 solo_reg_read(struct solo_dev *solo_dev, int reg)

--
Andrey Utkin
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Kernel-mentors@selenic.com
http://selenic.com/mailman/listinfo/kernel-mentors


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  reply	other threads:[~2015-03-02 14:12 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <f236217608b24a5e976628fe31d41a03@BRMWP-EXMB11.corp.brocade.com>
2015-02-12 14:48 ` Stephen Hemminger
2015-02-12 15:11   ` Andrey Utkin
2015-03-02 14:02     ` McKay, Luke [this message]
2015-03-03 14:29       ` Andrey Utkin
2015-03-04 16:03         ` McKay, Luke
2015-03-04 16:30           ` Roger Heflin
2015-03-04 17:04             ` McKay, Luke
2015-03-04 17:18               ` Roger Heflin
2015-02-11 18:19 Andrey Utkin

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