Ensure that the sync registers are cleared every time we restart the
ring to avoid stale values from creeping in from random neutrinos.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c 
b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 992889f9e0ff..81b10d85b738 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -529,6 +529,13 @@ static int init_ring_common(struct intel_engine_cs *engine)
 
        intel_engine_reset_breadcrumbs(engine);
 
+       if (HAS_LEGACY_SEMAPHORES(engine->i915)) {
+               I915_WRITE(RING_SYNC_0(engine->mmio_base), 0);
+               I915_WRITE(RING_SYNC_1(engine->mmio_base), 0);
+               if (HAS_VEBOX(dev_priv))
+                       I915_WRITE(RING_SYNC_2(engine->mmio_base), 0);
+       }
+
        /* Enforce ordering by reading HEAD register back */
        I915_READ_HEAD(engine);
 
-- 
2.20.0.rc1

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