[Intel-gfx] [PATCH v2 2/3] drm/i915/vlv: Added a rendering specific Hw WA 'WaReadAfterWriteHazard'

[akash.goel at intel.com]

From: Akash Goel <akash.goel at intel.com>

Added a new rendering specific Workaround 'WaReadAfterWriteHazard'.
In this WA, need to add 12 MI Store Dword commands to ensure proper
flush of h/w pipeline.

v2: Modified the WA comment (Ville)

Signed-off-by: Akash Goel <akash.goel at intel.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 2ac6600..49370a1 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2173,6 +2173,32 @@ intel_ring_flush_all_caches(struct intel_ring_buffer *ring)
 
 	trace_i915_gem_ring_flush(ring, 0, I915_GEM_GPU_DOMAINS);
 
+	if (IS_VALLEYVIEW(ring->dev)) {
+		/*
+		 * WaReadAfterWriteHazard
+		 * Send a number of Store Data commands here to finish
+		 * flushing hardware pipeline.This is needed in the case
+		 * where the next workload tries reading from the same
+		 * surface that this batch writes to. Without these StoreDWs,
+		 * not all of the data will actually be flushd to the surface
+		 * by the time the next batch starts reading it, possibly
+		 * causing a small amount of corruption.
+		 * FIXME, should also apply to snb, ivb.
+		 */
+		int i;
+		ret = intel_ring_begin(ring, 4 * 12);
+		if (ret)
+			return ret;
+		for (i = 0; i < 12; i++) {
+			intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
+			intel_ring_emit(ring, I915_GEM_HWS_SCRATCH_INDEX <<
+							MI_STORE_DWORD_INDEX_SHIFT);
+			intel_ring_emit(ring, 0);
+			intel_ring_emit(ring, MI_NOOP);
+		}
+		intel_ring_advance(ring);
+	}
+
 	ring->gpu_caches_dirty = false;
 	return 0;
 }
-- 
1.8.5.2