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

[Rob Clark]

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%7C86146416b717420501fc08da02c4785b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637825340130157925%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=LncI%2F5mIpeG1Avj2YXLmbZ5f1ONUfpf6TzJZH3%2Fs8%2Fw%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.

BR,
-R