On 2020-09-08 9:28 a.m., Tvrtko Ursulin wrote:

quoted

diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h

b/drivers/gpu/drm/i915/i915
index b7b59328cb76..9367ac801f0c 100644

--- a/drivers/gpu/drm/i915/i915_scatterlist.h
+++ b/drivers/gpu/drm/i915/i915_scatterlist.h

@@ -27,13 +27,19 @@ static __always_inline struct sgt_iter {

  } __sgt_iter(struct scatterlist *sgl, bool dma) {
         struct sgt_iter s = { .sgp = sgl };

+       if (sgl && !sg_dma_len(s.sgp))

I'd extend the condition to be, just to be safe:
    if (dma && sgl && !sg_dma_len(s.sgp))

Right, good catch, that's definitely necessary.

quoted

+               s.sgp = NULL;
+
         if (s.sgp) {
                 s.max = s.curr = s.sgp->offset;
-               s.max += s.sgp->length;
-               if (dma)
+
+               if (dma) {
+                       s.max += sg_dma_len(s.sgp);
                         s.dma = sg_dma_address(s.sgp);
-               else
+               } else {
+                       s.max += s.sgp->length;
                         s.pfn = page_to_pfn(sg_page(s.sgp));
+               }

Otherwise has this been tested or alternatively how to test it? (How to
repro the issue.)

It has not been tested. To test it, you need Tom's patch set without the
last "DO NOT MERGE" patch:

https://lkml.kernel.org/lkml/20200907070035.GA25114@infradead.org/T/

Thanks,

Logan

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