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drm/i915: Reset the HEAD pointer for the ring after writing START

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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@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Chris Wilson 2014-08-07 15:39:54 +01:00 committed by Daniel Vetter
parent 4ad72b7fad
commit 95468892fd
1 changed files with 8 additions and 0 deletions
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8
drivers/gpu/drm/i915/intel_ringbuffer.c
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@ -563,6 +563,14 @@ 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);