[Intel-gfx] [PATCH] drm/i915: Always retire residual requests before suspend

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-07-18 13:53:16)
> 
> On 17/07/2018 09:41, Chris Wilson wrote:
> > If the driver is wedged, we skip idling the GPU. However, we may still
> > have a few requests still not retired following the wedging (since they
> > will be waiting for a background worker trying to acquire struct_mutex).
> > As we hold the struct_mutex, always do a quick request retirement in
> > order to flush the wedged path.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107257
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >   drivers/gpu/drm/i915/i915_gem.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 42d24410a98c..cc875e1dc7f6 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -5074,6 +5074,8 @@ int i915_gem_suspend(struct drm_i915_private *i915)
> >   
> >               assert_kernel_context_is_current(i915);
> >       }
> > +     i915_retire_requests(i915); /* ensure we flush after wedging */
> > +
> 
> We cannot do this in i915_gem_set_wedged due not having the mutex?

Correct.

> I think it should go in an else block of the !terminally_wedged block to 
> signify the alternative idling method for that case. And also to make 
> sure the !terminally_wedged case does not start relying on this extra 
> retire pass.

I liked the safety net and clarity of not making it conditional.

> Or alternative teach i915_gem_wait_for_idle how to handle the wedged 
> case and only make switching to kernel context dependant on 
> terminally_wedged status in i915_gem_suspend?

Right, it's the checks that actually worry here. Those depend on the gpu
being in a fairly sane state...
-Chris