drm/i915/guc: Flush G2H handler during a GT reset

Now that the error capture is fully decoupled from fence signalling
(request retirement to free memory, which in turn depends on resets) we
can safely flush the G2H handler during a GT reset. This eliminates
corner cases where GuC generated G2H (e.g. engine resets) race with a GT
reset.

v2:
 (John Harrison)
  - Fix typo in commit message (s/is/in)
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220121043118.24886-4-matthew.brost@intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c

@@ -1395,8 +1395,6 @@ static void guc_flush_destroyed_contexts(struct intel_guc *guc);
 
 void intel_guc_submission_reset_prepare(struct intel_guc *guc)
 {
-	int i;
-
 	if (unlikely(!guc_submission_initialized(guc))) {
 		/* Reset called during driver load? GuC not yet initialised! */
 		return;
@@ -1413,21 +1411,7 @@ void intel_guc_submission_reset_prepare(struct intel_guc *guc)
 
 	guc_flush_submissions(guc);
 	guc_flush_destroyed_contexts(guc);
-
-	/*
-	 * Handle any outstanding G2Hs before reset. Call IRQ handler directly
-	 * each pass as interrupt have been disabled. We always scrub for
-	 * outstanding G2H as it is possible for outstanding_submission_g2h to
-	 * be incremented after the context state update.
-	 */
-	for (i = 0; i < 4 && atomic_read(&guc->outstanding_submission_g2h); ++i) {
-		intel_guc_to_host_event_handler(guc);
-#define wait_for_reset(guc, wait_var) \
-		intel_guc_wait_for_pending_msg(guc, wait_var, false, (HZ / 20))
-		do {
-			wait_for_reset(guc, &guc->outstanding_submission_g2h);
-		} while (!list_empty(&guc->ct.requests.incoming));
-	}
+	flush_work(&guc->ct.requests.worker);
 
 	scrub_guc_desc_for_outstanding_g2h(guc);
 }