[Intel-xe] [PATCH] drm/xe: fix tlb_invalidation_seqno_past()

[Matthew Auld]

Checking seqno_recv >= seqno looks like it will incorrectly report true
when the seqno has wrapped (not unlikely given
TLB_INVALIDATION_SEQNO_MAX). Calling xe_gt_tlb_invalidation_wait() might
then return before the flush has been completed by the GuC.

Fix this by treating a large negative delta as an indication that the
seqno has wrapped around. Similar to how we treat a large positive delta
as an indication that the seqno_recv must have wrapped around, but in
that case the seqno has likely also signalled.

It looks like we could also potentially make the seqno use the full
32bits as supported by the GuC.

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Cc: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
index 604f189dbd70..67822b3dd353 100644
--- a/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
+++ b/drivers/gpu/drm/xe/xe_gt_tlb_invalidation.c
@@ -251,14 +251,15 @@ int xe_gt_tlb_invalidation_vma(struct xe_gt *gt,
 
 static bool tlb_invalidation_seqno_past(struct xe_gt *gt, int seqno)
 {
-	if (gt->tlb_invalidation.seqno_recv >= seqno)
-		return true;
+	if (seqno - gt->tlb_invalidation.seqno_recv <
+	    -(TLB_INVALIDATION_SEQNO_MAX / 2))
+		return false;
 
 	if (seqno - gt->tlb_invalidation.seqno_recv >
 	    (TLB_INVALIDATION_SEQNO_MAX / 2))
 		return true;
 
-	return false;
+	return gt->tlb_invalidation.seqno_recv >= seqno;
 }
 
 /**
-- 
2.40.0