+ struct intel_engine_cs *engine = req->engine;
+
+ /* Before we do the heavier coherent read of the seqno,
+ * check the value (hopefully) in the CPU cacheline.
+ */
+ if (i915_gem_request_completed(req))
+ return true;
+
+ /* Ensure our read of the seqno is coherent so that we
+ * do not "miss an interrupt" (i.e. if this is the last
+ * request and the seqno write from the GPU is not visible
+ * by the time the interrupt fires, we will see that the
+ * request is incomplete and go back to sleep awaiting
+ * another interrupt that will never come.)
+ *
+ * Strictly, we only need to do this once after an interrupt,
+ * but it is easier and safer to do it every time the waiter
+ * is woken.
+ */
+ if (engine->irq_seqno_barrier &&
+ READ_ONCE(engine->breadcrumbs.irq_seqno_bh) == current &&
+ cmpxchg_relaxed(&engine->breadcrumbs.irq_posted, 1, 0)) {
+ struct task_struct *tsk;
+
+ /* The ordering of irq_posted versus applying the barrier
+ * is crucial. The clearing of the current irq_posted must
+ * be visible before we perform the barrier operation,
+ * such that if a subsequent interrupt arrives, irq_posted
+ * is reasserted and our task rewoken (which causes us to
+ * do another __i915_request_irq_complete() immediately
+ * and reapply the barrier). Conversely, if the clear
+ * occurs after the barrier, then an interrupt that arrived
+ * whilst we waited on the barrier would not trigger a
+ * barrier on the next pass, and the read may not see the
+ * seqno update.
+ */
+ engine->irq_seqno_barrier(engine);
+
+ /* If we consume the irq, but we are no longer the bottom-half,
+ * the real bottom-half may not have serialised their own
+ * seqno check with the irq-barrier (i.e. may have inspected
+ * the seqno before we believe it coherent since they see
+ * irq_posted == false but we are still running).
+ */
+ rcu_read_lock();
+ tsk = READ_ONCE(engine->breadcrumbs.irq_seqno_bh);
+ if (tsk && tsk != current)
+ /* Note that if the bottom-half is changed as we
+ * are sending the wake-up, the new bottom-half will
+ * be woken by whomever made the change. We only have
+ * to worry about when we steal the irq-posted for
+ * ourself.
+ */
+ wake_up_process(tsk);
+ rcu_read_unlock();
+
+ if (i915_gem_request_completed(req))
+ return true;
+ }
+
+ /* We need to check whether any gpu reset happened in between
+ * the request being submitted and now. If a reset has occurred,
+ * the seqno will have been advance past ours and our request
+ * is complete. If we are in the process of handling a reset,
+ * the request is effectively complete as the rendering will
+ * be discarded, but we need to return in order to drop the
+ * struct_mutex.
+ */
+ if (i915_reset_in_progress(&req->i915->gpu_error))
+ return true;
+
+ return false;