drm/i915: Check the ring is empty when declaring the engines are idle

As another precaution when testing whether the CS engine is actually
idle, also inspect the ring's HEAD/TAIL registers, which should be equal
when there are no commands left to execute by the GPU.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170530121334.17364-3-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 699f2d3861c7..bc38bd128b76 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1212,6 +1212,11 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
 
         intel_runtime_pm_get(dev_priv);
 
+        /* First check that no commands are left in the ring */
+        if ((I915_READ_HEAD(engine) & HEAD_ADDR) !=
+            (I915_READ_TAIL(engine) & TAIL_ADDR))
+                idle = false;
+
         /* No bit for gen2, so assume the CS parser is idle */
         if (INTEL_GEN(dev_priv) > 2 && !(I915_READ_MODE(engine) & MODE_IDLE))
                 idle = false;