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Subject[PATCH] drm/amdgpu: limit DMA size to PAGE_SIZE for scatter-gather buffers
Date
Code is expecing to observe the same number of buffers returned from
dma_map_sg() function compared to sg_alloc_table_from_pages(). This
doesn't hold true universally especially for systems with IOMMU.

IOMMU driver tries to combine buffers into a single DMA address as much
as it can. The right thing is to tell the DMA layer how much combining
IOMMU can do.

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index e4bb435..02465cd 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -787,6 +787,8 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
enum dma_data_direction direction = write ?
DMA_BIDIRECTIONAL : DMA_TO_DEVICE;

+ dma_set_max_seg_size(adev->dev, PAGE_SIZE);
+
r = sg_alloc_table_from_pages(ttm->sg, ttm->pages, ttm->num_pages, 0,
ttm->num_pages << PAGE_SHIFT,
GFP_KERNEL);
--
2.7.4
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