[PATCH v2 2/3] drm/amdgpu: Allow dma_map_sg() coalescing

[Robin Murphy]

The amdgpu driver doesn't appear to directly use the scatterlist mapped
by amdgpu_ttm_tt_pin_userptr(), it merely hands it off to
drm_prime_sg_to_page_addr_arrays() to generate the dma_address array
which it actually cares about. Now that the latter can cope with
dma_map_sg() coalescing dma-contiguous segments such that it returns
0 < count < nents, we can relax the current count == nents check to
only consider genuine failure as other drivers do.

This avoids a false negative on arm64 systems with an IOMMU.

Reported-by: Sinan Kaya <okaya at codeaurora.org>
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---

v2: Expand commit message to clarify

 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 205da3ff9cd0..f81e96a4242f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -813,7 +813,7 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
 
 	r = -ENOMEM;
 	nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
-	if (nents != ttm->sg->nents)
+	if (nents == 0)
 		goto release_sg;
 
 	drm_prime_sg_to_page_addr_arrays(ttm->sg, ttm->pages,
-- 
2.16.1.dirty