[Intel-gfx] [PATCH 2/6] drm/i915/execlists: Check the sentinel is alone in the ELSP

[Chris Wilson]

We only use sentinel requests for "preempt-to-idle" passes, so assert
that they are the only request in a new submission.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c 
b/drivers/gpu/drm/i915/gt/intel_lrc.c
index ba31cbe8c68e..f2c49dc1e6b4 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1448,6 +1448,7 @@ assert_pending_valid(const struct intel_engine_execlists 
*execlists,
 {
        struct i915_request * const *port, *rq;
        struct intel_context *ce = NULL;
+       bool sentinel = false;
 
        trace_ports(execlists, msg, execlists->pending);
 
@@ -1481,6 +1482,26 @@ assert_pending_valid(const struct intel_engine_execlists 
*execlists,
                }
                ce = rq->context;
 
+               /*
+                * Sentinels are supposed to be lonely so they flush the
+                * current exection off the HW. Check that they are the
+                * only request in the pending submission.
+                */
+               if (sentinel) {
+                       GEM_TRACE_ERR("context:%llx after sentinel in 
pending[%zd]\n",
+                                     ce->timeline->fence_context,
+                                     port - execlists->pending);
+                       return false;
+               }
+
+               sentinel = i915_request_has_sentinel(rq);
+               if (sentinel && port != execlists->pending) {
+                       GEM_TRACE_ERR("sentinel context:%llx not in prime 
position[%zd]\n",
+                                     ce->timeline->fence_context,
+                                     port - execlists->pending);
+                       return false;
+               }
+
                /* Hold tightly onto the lock to prevent concurrent retires! */
                if (!spin_trylock_irqsave(&rq->lock, flags))
                        continue;
-- 
2.25.0

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