* [PATCH] drm/amdgpu: limit DMA size to PAGE_SIZE for scatter-gather buffers
@ 2018-04-10 18:25 Sinan Kaya
2018-04-10 18:49 ` Christian König
0 siblings, 1 reply; 2+ messages in thread
From: Sinan Kaya @ 2018-04-10 18:25 UTC (permalink / raw)
To: amd-gfx, timur, sulrich
Cc: Tom St Denis, David (ChunMing) Zhou, David Airlie, linux-arm-msm,
Felix Kuehling, Michel Dänzer, open list,
open list:DRM DRIVERS, Sinan Kaya, Harish Kasiviswanathan,
Roger He, Monk Liu, Alex Deucher, Christian König,
linux-arm-kernel
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] drm/amdgpu: limit DMA size to PAGE_SIZE for scatter-gather buffers
2018-04-10 18:25 [PATCH] drm/amdgpu: limit DMA size to PAGE_SIZE for scatter-gather buffers Sinan Kaya
@ 2018-04-10 18:49 ` Christian König
0 siblings, 0 replies; 2+ messages in thread
From: Christian König @ 2018-04-10 18:49 UTC (permalink / raw)
To: Sinan Kaya, amd-gfx, timur, sulrich
Cc: Tom St Denis, David (ChunMing) Zhou, David Airlie, linux-arm-msm,
Felix Kuehling, Michel Dänzer, open list,
open list:DRM DRIVERS, Harish Kasiviswanathan, Roger He,
Monk Liu, Alex Deucher, linux-arm-kernel
Am 10.04.2018 um 20:25 schrieb Sinan Kaya:
> 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.
Good catch, but wrong place to set this.
Please move it into the device initialization functions.
Regards,
Christian.
>
> 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);
^ permalink raw reply [flat|nested] 2+ messages in thread
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