drm/i915/gt: Replace open-coded intel_engine_stop_cs()

In the legacy ringbuffer submission, we still had an open-coded version
of intel_engine_stop_cs() with one additional verification step. Transfer
that verification to intel_engine_stop_cs() itself, and call it.
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/20210113204709.15020-1-chris@chris-wilson.co.uk

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

@@ -1054,8 +1054,19 @@ int intel_engine_stop_cs(struct intel_engine_cs *engine)
 
 	ENGINE_TRACE(engine, "\n");
 	if (__intel_engine_stop_cs(engine, 1000, stop_timeout(engine))) {
-		ENGINE_TRACE(engine, "timed out on STOP_RING -> IDLE\n");
-		err = -ETIMEDOUT;
+		ENGINE_TRACE(engine,
+			     "timed out on STOP_RING -> IDLE; HEAD:%04x, TAIL:%04x\n",
+			     ENGINE_READ_FW(engine, RING_HEAD) & HEAD_ADDR,
+			     ENGINE_READ_FW(engine, RING_TAIL) & TAIL_ADDR);
+
+		/*
+		 * Sometimes we observe that the idle flag is not
+		 * set even though the ring is empty. So double
+		 * check before giving up.
+		 */
+		if ((ENGINE_READ_FW(engine, RING_HEAD) & HEAD_ADDR) !=
+		    (ENGINE_READ_FW(engine, RING_TAIL) & TAIL_ADDR))
+			err = -ETIMEDOUT;
 	}
 
 	return err;

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

@@ -159,30 +159,7 @@ static void ring_setup_status_page(struct intel_engine_cs *engine)
 
 static bool stop_ring(struct intel_engine_cs *engine)
 {
-	struct drm_i915_private *dev_priv = engine->i915;
-
-	if (INTEL_GEN(dev_priv) > 2) {
-		ENGINE_WRITE(engine,
-			     RING_MI_MODE, _MASKED_BIT_ENABLE(STOP_RING));
-		if (intel_wait_for_register(engine->uncore,
-					    RING_MI_MODE(engine->mmio_base),
-					    MODE_IDLE,
-					    MODE_IDLE,
-					    1000)) {
-			drm_err(&dev_priv->drm,
-				"%s : timed out trying to stop ring\n",
-				engine->name);
-
-			/*
-			 * Sometimes we observe that the idle flag is not
-			 * set even though the ring is empty. So double
-			 * check before giving up.
-			 */
-			if (ENGINE_READ(engine, RING_HEAD) !=
-			    ENGINE_READ(engine, RING_TAIL))
-				return false;
-		}
-	}
+	intel_engine_stop_cs(engine);
 
 	ENGINE_WRITE(engine, RING_HEAD, ENGINE_READ(engine, RING_TAIL));