[PATCH 6/6] drm/i915: Fix DMA mapped scatterlist iteration

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

When walking DMA mapped scatterlists sg_dma_len has to be used since it
can be different (coalesced) from the backing store entry.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Fixes: 85d1225ec066 ("drm/i915: Introduce & use new lightweight SGL iterators")
Reported-by: Tom Murphy <murphyt7 at tcd.ie>
Suggested-by: Logan Gunthorpe <logang at deltatee.com>
---
 drivers/gpu/drm/i915/i915_scatterlist.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h b/drivers/gpu/drm/i915/i915_scatterlist.h
index b7b59328cb76..510856887628 100644
--- a/drivers/gpu/drm/i915/i915_scatterlist.h
+++ b/drivers/gpu/drm/i915/i915_scatterlist.h
@@ -27,13 +27,17 @@ static __always_inline struct sgt_iter {
 } __sgt_iter(struct scatterlist *sgl, bool dma) {
 	struct sgt_iter s = { .sgp = sgl };
 
-	if (s.sgp) {
+	if (dma && s.sgp && sg_dma_len(s.sgp) == 0) {
+		s.sgp = NULL;
+	} else if (s.sgp) {
 		s.max = s.curr = s.sgp->offset;
-		s.max += s.sgp->length;
-		if (dma)
+		if (dma) {
 			s.dma = sg_dma_address(s.sgp);
-		else
+			s.max += sg_dma_len(s.sgp);
+		} else {
 			s.pfn = page_to_pfn(sg_page(s.sgp));
+			s.max += s.sgp->length;
+		}
 	}
 
 	return s;
-- 
2.25.1