[Intel-gfx] [PATCH] drm/i915: Double check ring is idle before declaring the GPU wedged

[Chris Wilson]

On Mon, Aug 11, 2014 at 11:07:10AM +0100, Damien Lespiau wrote:
> On Mon, Aug 11, 2014 at 10:35:25AM +0100, Chris Wilson wrote:
> > On Mon, Aug 11, 2014 at 10:30:09AM +0100, Damien Lespiau wrote:
> > > On Mon, Aug 11, 2014 at 09:21:35AM +0100, Chris Wilson wrote:
> > > > During ring initialisation, sometimes we observe, though not in
> > > > production hardware, that the idle flag is not set even though the ring
> > > > is empty. Double check before giving up.
> > > > 
> > > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > > Cc: Damien Lespiau <damien.lespiau at intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/intel_ringbuffer.c | 7 ++++++-
> > > >  1 file changed, 6 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > index a0831c309eab..d72d5e0e693d 100644
> > > > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > @@ -467,7 +467,12 @@ static bool stop_ring(struct intel_engine_cs *ring)
> > > >  		I915_WRITE_MODE(ring, _MASKED_BIT_ENABLE(STOP_RING));
> > > >  		if (wait_for((I915_READ_MODE(ring) & MODE_IDLE) != 0, 1000)) {
> > > >  			DRM_ERROR("%s : timed out trying to stop ring\n", ring->name);
> > > > -			return false;
> > > > +			/* Sometimes we observe that the idle flag is not
> > > > +			 * set even though the ring is empty. So double
> > > > +			 * check before giving up.
> > > > +			 */
> > > > +			if (I915_READ_HEAD(ring) != I915_READ_TAIL(ring))
> > > > +				return false;
> > > 
> > > That means we propably want to just put the user visible error message
> > > there as well?
> > 
> > It is still a 1 second timeout, so having a warning there that something
> > is wrong is important I thought.
> 
> Ah, I missed the "not in production hw" bits of the commit message, It
> may mean simulation and then the guess is that flag is not implemented.
> If that makes us not totally give up, I guess that's something.

I was trying to avoid saying that it was only to work around sim bugs :)
Otherwise, it looks to be a useful piece of paranoia and logging against
hw trying to screw us over.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre