[Intel-gfx] [PATCH] drm/i915: Reset the HEAD pointer for the ring after writing START

[Daniel Vetter]

On Thu, Aug 07, 2014 at 07:05:49PM +0300, Ville Syrjälä wrote:
> On Thu, Aug 07, 2014 at 03:39:54PM +0100, Chris Wilson wrote:
> > Ville found an old w/a documented for g4x that suggested that we need to
> > reset the HEAD after writing START. This is a useful fixup for some of
> > the g4x ring initialisation woes, but as usual, not all.
> > 
> > v2: Do the rewrite unconditionally anyway
> > 
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=76554
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Yeah looks sensible to me. So based on my gut feeling just from the
> seeing the w/a name this is:
> 
> Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Queued for -next, thanks for the patch. Although if a tested-by shows up
we should really throw this one into -fixes, since the current duct-tape
still seems to be less effective than whatever kept things working
previously.
-Daniel

> 
> > ---
> >  drivers/gpu/drm/i915/intel_ringbuffer.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > index 45e3ec927051..26ec25afc02a 100644
> > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > @@ -537,6 +537,14 @@ static int init_ring_common(struct intel_engine_cs *ring)
> >  	 * also enforces ordering), otherwise the hw might lose the new ring
> >  	 * register values. */
> >  	I915_WRITE_START(ring, i915_gem_obj_ggtt_offset(obj));
> > +
> > +	/* WaClearRingBufHeadRegAtInit:ctg,elk */
> > +	if (I915_READ_HEAD(ring))
> > +		DRM_DEBUG("%s initialization failed [head=%08x], fudging\n",
> > +			  ring->name, I915_READ_HEAD(ring));
> > +	I915_WRITE_HEAD(ring, 0);
> > +	(void)I915_READ_HEAD(ring);
> > +
> >  	I915_WRITE_CTL(ring,
> >  			((ringbuf->size - PAGE_SIZE) & RING_NR_PAGES)
> >  			| RING_VALID);
> > -- 
> > 2.1.0.rc1
> 
> -- 
> Ville Syrjälä
> Intel OTC
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch