[PATCH v2 1/2] drm: Add GPU reset sysfs event

[Sharma, Shashank]

On 3/10/2022 8:35 PM, Rob Clark wrote:
> On Thu, Mar 10, 2022 at 11:14 AM Sharma, Shashank
> <shashank.sharma at amd.com> wrote:
>>
>>
>>
>> On 3/10/2022 7:33 PM, Abhinav Kumar wrote:
>>>
>>>
>>> On 3/10/2022 9:40 AM, Rob Clark wrote:
>>>> On Thu, Mar 10, 2022 at 9:19 AM Sharma, Shashank
>>>> <shashank.sharma at amd.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 3/10/2022 6:10 PM, Rob Clark wrote:
>>>>>> On Thu, Mar 10, 2022 at 8:21 AM Sharma, Shashank
>>>>>> <shashank.sharma at amd.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 3/10/2022 4:24 PM, Rob Clark wrote:
>>>>>>>> On Thu, Mar 10, 2022 at 1:55 AM Christian König
>>>>>>>> <ckoenig.leichtzumerken at gmail.com> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Am 09.03.22 um 19:12 schrieb Rob Clark:
>>>>>>>>>> On Tue, Mar 8, 2022 at 11:40 PM Shashank Sharma
>>>>>>>>>> <contactshashanksharma at gmail.com> wrote:
>>>>>>>>>>> From: Shashank Sharma <shashank.sharma at amd.com>
>>>>>>>>>>>
>>>>>>>>>>> This patch adds a new sysfs event, which will indicate
>>>>>>>>>>> the userland about a GPU reset, and can also provide
>>>>>>>>>>> some information like:
>>>>>>>>>>> - process ID of the process involved with the GPU reset
>>>>>>>>>>> - process name of the involved process
>>>>>>>>>>> - the GPU status info (using flags)
>>>>>>>>>>>
>>>>>>>>>>> This patch also introduces the first flag of the flags
>>>>>>>>>>> bitmap, which can be appended as and when required.
>>>>>>>>>> Why invent something new, rather than using the already existing
>>>>>>>>>> devcoredump?
>>>>>>>>>
>>>>>>>>> Yeah, that's a really valid question.
>>>>>>>>>
>>>>>>>>>> I don't think we need (or should encourage/allow) something drm
>>>>>>>>>> specific when there is already an existing solution used by both
>>>>>>>>>> drm
>>>>>>>>>> and non-drm drivers.  Userspace should not have to learn to support
>>>>>>>>>> yet another mechanism to do the same thing.
>>>>>>>>>
>>>>>>>>> Question is how is userspace notified about new available core
>>>>>>>>> dumps?
>>>>>>>>
>>>>>>>> I haven't looked into it too closely, as the CrOS userspace
>>>>>>>> crash-reporter already had support for devcoredump, so it "just
>>>>>>>> worked" out of the box[1].  I believe a udev event is what triggers
>>>>>>>> the crash-reporter to go read the devcore dump out of sysfs.
>>>>>>>
>>>>>>> I had a quick look at the devcoredump code, and it doesn't look like
>>>>>>> that is sending an event to the user, so we still need an event to
>>>>>>> indicate a GPU reset.
>>>>>>
>>>>>> There definitely is an event to userspace, I suspect somewhere down
>>>>>> the device_add() path?
>>>>>>
>>>>>
>>>>> Let me check that out as well, hope that is not due to a driver-private
>>>>> event for GPU reset, coz I think I have seen some of those in a few DRM
>>>>> drivers.
>>>>>
>>>>
>>>> Definitely no driver private event for drm/msm .. I haven't dug
>>>> through it all but this is the collector for devcoredump, triggered
>>>> somehow via udev.  Most likely from event triggered by device_add()
>>>>
>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fchromium.googlesource.com%2Fchromiumos%2Fplatform2%2F%2B%2FHEAD%2Fcrash-reporter%2Fudev_collector.cc&data=04%7C01%7Cshashank.sharma%40amd.com%7Cb4e920f125ae4d7de29708da02cd3112%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637825377562005233%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=M4xHPErex4vn7l3lNPgniiMp%2BKb3SpOHQo2QLAndxDQ%3D&reserved=0
>>>>
>>>
>>> Yes, that is correct. the uevent for devcoredump is from device_add()
>>>
>> Yes, I could confirm in the code that device_add() sends a uevent.
>>
>> kobject_uevent(&dev->kobj, KOBJ_ADD);
>>
>> I was trying to map the ChromiumOs's udev event rules with the event
>> being sent from device_add(), what I could see is there is only one udev
>> rule for any DRM subsystem events in ChromiumOs's 99-crash-reporter.rules:
>>
>> ACTION=="change", SUBSYSTEM=="drm", KERNEL=="card0", ENV{ERROR}=="1", \
>>     RUN+="/sbin/crash_reporter
>> --udev=KERNEL=card0:SUBSYSTEM=drm:ACTION=change"
>>
>> Can someone confirm that this is the rule which gets triggered when a
>> devcoredump is generated ? I could not find an ERROR=1 string in the
>> env[] while sending this event from dev_add();
> 
> I think it is actually this rule:
> 
> ACTION=="add", SUBSYSTEM=="devcoredump", \
>    RUN+="/sbin/crash_reporter
> --udev=SUBSYSTEM=devcoredump:ACTION=add:KERNEL_NUMBER=%n"
> 
> It is something non-drm specific because it supports devcore dumps
> from non drm drivers.  I know at least some of the wifi and remoteproc
> drivers use it.
> 

Ah, this seems like a problem for me. I understand it will work for a 
reset/recovery app well, but if a DRM client (like a compositor), who 
wants to listen only to DRM events (like a GPU reset), wouldn't this 
create a lot of noise for it ? Like every time any subsystem produces 
this coredump, there will be a change in devcoresump subsystem, and the 
client will have to parse the core file, and then will have to decide if 
it wants to react to this, or ignore.

Wouldn't a GPU reset event, specific to DRM subsystem server better in 
such case ?

- Shashank

> BR,
> -R