drm/i915/execlists: Reduce completed event mask to COMPLETE | PREEMPTED

Since we get a COMPLETE event when the context switch occurs on
RING_HEAD == RING_TAIL and a PREEMPTED event when a switch occurs
before that point, COMPLETE | PREEMPTED should cover all possible context
switch completion events. We can move the ELEMENT_SWITCH info message
from the COMPLETED_MASK into an assertion for when we are performing a
switch to port[1].

Suggested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171120123458.23242-2-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_lrc.c

@@ -154,9 +154,7 @@
 #define GEN8_CTX_STATUS_LITE_RESTORE	(1 << 15)
 
 #define GEN8_CTX_STATUS_COMPLETED_MASK \
-	 (GEN8_CTX_STATUS_COMPLETE | \
-	  GEN8_CTX_STATUS_PREEMPTED | \
-	  GEN8_CTX_STATUS_ELEMENT_SWITCH)
+	 (GEN8_CTX_STATUS_COMPLETE | GEN8_CTX_STATUS_PREEMPTED)
 
 #define CTX_LRI_HEADER_0		0x01
 #define CTX_CONTEXT_CONTROL		0x02
@@ -907,6 +905,8 @@ static void execlists_submission_tasklet(unsigned long data)
 			GEM_BUG_ON(count == 0);
 			if (--count == 0) {
 				GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
+				GEM_BUG_ON(port_isset(&port[1]) &&
+					   !(status & GEN8_CTX_STATUS_ELEMENT_SWITCH));
 				GEM_BUG_ON(!i915_gem_request_completed(rq));
 				execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);