[Intel-gfx] [PATCH 7/7] drm/i915: Simplify check for idleness in hangcheck

[Chris Wilson]

On Wed, Apr 06, 2016 at 12:32:29PM +0300, Mika Kuoppala wrote:
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > [ text/plain ]
> > Having fixed the tracking of the engine's last_submitted_seqno, we can
> > now rely on it for detecting when the engine is idle (and not have to
> > touch the requests pointer).
> >
> > Testcase: igt/gem_exec_whisper
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_irq.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index c85eb8dec2dc..a56be4f92264 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -2805,8 +2805,7 @@ static void gen8_disable_vblank(struct drm_device *dev, unsigned int pipe)
> >  static bool
> >  ring_idle(struct intel_engine_cs *engine, u32 seqno)
> >  {
> > -	return (list_empty(&engine->request_list) ||
> > -		i915_seqno_passed(seqno, engine->last_submitted_seqno));
> > +	return i915_seqno_passed(seqno, engine->last_submitted_seqno);
> 
> My concern here is that we should move the write for the
> last_submitted_seqno before we push the work into ring.
> 
> To guarantee that the driver never sees a seqno > last_submitted_seqno
> on particular ring.

Reasonable request. You'll want a smp_store_mb() on the
last_submitted_seqno as well with a comment
/* barrier for hangcheck */

In return what's up with the Braswell?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre