drm/i915/ringbuffer: Clear semaphore sync registers on ring init

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

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108888
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181203113701.12106-3-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 28ae1e436ea638cb93a302c1152440a16f75c365..d81eaf5f6b3e1e375d752606c1dce3e86f39a955 100644 (file)
--- 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);