drm/i915/execlists: Pause CS flow before reset

Since we may be attempting to reset an active engine, we try to freeze
it in place before resetting -- to be on the safe side. We can go one
step further if we are using the CS flow semaphore to prevent the
context switching into the next.
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/20200331091459.29179-2-chris@chris-wilson.co.uk

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

@@ -3683,6 +3683,7 @@ static void execlists_reset_prepare(struct intel_engine_cs *engine)
 	 *
 	 * FIXME: Wa for more modern gens needs to be validated
 	 */
+	ring_set_paused(engine, 1);
 	intel_engine_stop_cs(engine);
 }