On Sat, Nov 05, 2016 at 10:36:00AM +0200, Imre Deak wrote: > We assume that the GPU is idle once receiving the seqno via the last > request's user interrupt. In execlist mode the corresponding context > completed interrupt can be delayed though and until this latter > interrupt arrives we consider the request to be pending on the ELSP > submit port. This can cause a problem during system suspend where this > last request will be seen by the resume code as still pending. Such > pending requests are normally replayed after a GPU reset, but during > resume we reset both SW and HW tracking of the ring head/tail pointers, > so replaying the pending request with its stale tail pointer will leave > the ring in an inconsistent state. A subsequent request submission can > lead then to the GPU executing from uninitialized area in the ring > behind the above stale tail pointer. > > Fix this by making sure any pending request on the ELSP port is > completed before suspending. I used a polling wait since the completion > time I measured was <1ms and since normally we only need to wait during > system suspend. GPU idling during runtime suspend is scheduled with a > delay (currently 50-100ms) after the retirement of the last request at > which point the context completed interrupt must have arrived already. > > The chance of this bug was increased by > > commit 1c777c5d1dcdf8fa0223fcff35fb387b5bb9517a > Author: Imre Deak <imre.deak@xxxxxxxxx> > Date: Wed Oct 12 17:46:37 2016 +0300 > > drm/i915/hsw: Fix GPU hang during resume from S3-devices state > > but it could happen even without the explicit GPU reset, since we > disable interrupts afterwards during the suspend sequence. > > v2: > - Do an unlocked poll-wait first. (Chris) > v3-4: > - s/intel_lr_engines_idle/intel_execlists_idle/ and move > i915.enable_execlists check to the new helper. (Chris) > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98470 > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
