drm/i915/execlists: Check the sentinel is alone in the ELSP

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 <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200302085812.4172450-12-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 15d56cd..b9b3f78 100644 (file)
--- 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;