drm/i915/execlists: Peek at the next submission for error interrupts

If we receive the error interrupt before the CS interrupt, we may find
ourselves without an active request to reset, skipping the GPU reset.
All because the attempt to reset was too early.
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/20200401110435.30389-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -2804,6 +2804,45 @@ static struct execlists_capture *capture_regs(struct intel_engine_cs *engine)
 	return NULL;
 }
 
+static struct i915_request *
+active_context(struct intel_engine_cs *engine, u32 ccid)
+{
+	const struct intel_engine_execlists * const el = &engine->execlists;
+	struct i915_request * const *port, *rq;
+
+	/*
+	 * Use the most recent result from process_csb(), but just in case
+	 * we trigger an error (via interrupt) before the first CS event has
+	 * been written, peek at the next submission.
+	 */
+
+	for (port = el->active; (rq = *port); port++) {
+		if (upper_32_bits(rq->context->lrc_desc) == ccid) {
+			ENGINE_TRACE(engine,
+				     "ccid found at active:%zd\n",
+				     port - el->active);
+			return rq;
+		}
+	}
+
+	for (port = el->pending; (rq = *port); port++) {
+		if (upper_32_bits(rq->context->lrc_desc) == ccid) {
+			ENGINE_TRACE(engine,
+				     "ccid found at pending:%zd\n",
+				     port - el->pending);
+			return rq;
+		}
+	}
+
+	ENGINE_TRACE(engine, "ccid:%x not found\n", ccid);
+	return NULL;
+}
+
+static u32 active_ccid(struct intel_engine_cs *engine)
+{
+	return ENGINE_READ_FW(engine, RING_EXECLIST_STATUS_HI);
+}
+
 static bool execlists_capture(struct intel_engine_cs *engine)
 {
 	struct execlists_capture *cap;
@@ -2821,7 +2860,7 @@ static bool execlists_capture(struct intel_engine_cs *engine)
 		return true;
 
 	spin_lock_irq(&engine->active.lock);
-	cap->rq = execlists_active(&engine->execlists);
+	cap->rq = active_context(engine, active_ccid(engine));
 	if (cap->rq) {
 		cap->rq = active_request(cap->rq->context->timeline, cap->rq);
 		cap->rq = i915_request_get_rcu(cap->rq);