drm/xe: Don't process TLB invalidation done in CT fast-path

We can't currently do this due to TLB invalidation done handler
expecting the seqno being received in-order, with the fast-path a TLB
invalidation done could pass one being processed in the slow-path in an
extreme corner case. Remove TLB invalidation done from the fast-path for
now and in a follow up reenable this once the TLB invalidation done
handler can deal with out of order seqno.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_guc_ct.c

@@ -966,7 +966,14 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
 			return 0;
 
 		switch (FIELD_GET(GUC_HXG_EVENT_MSG_0_ACTION, msg[1])) {
-		case XE_GUC_ACTION_TLB_INVALIDATION_DONE:
+		/*
+		 * FIXME: We really should process
+		 * XE_GUC_ACTION_TLB_INVALIDATION_DONE here in the fast-path as
+		 * these critical for page fault performance. We currently can't
+		 * due to TLB invalidation done algorithm expecting the seqno
+		 * returned in-order. With some small changes to the algorithm
+		 * and locking we should be able to support out-of-order seqno.
+		 */
 		case XE_GUC_ACTION_REPORT_PAGE_FAULT_REQ_DESC:
 			break;	/* Process these in fast-path */
 		default: