On 12/12/25 2:23 PM, Christian König wrote:
On 12/12/25 07:40, Donet Tom wrote:
The SDMA engine has a hardware limitation of 4 MB maximum transfer
size per operation.
That is not correct. This is only true on ancient HW.
What problems are you seeing here?
AMDGPU_GTT_MAX_TRANSFER_SIZE was hardcoded to
512 pages, which worked correctly on systems with 4K pages but fails
on systems with larger page sizes.
This patch divides the max transfer size / AMDGPU_GPU_PAGES_IN_CPU_PAGE
to match with non-4K page size systems.
That is actually a bad idea. The value was meant to match the PMD size.
Hi Christian, Felix, Alex and philip
Instead of hardcoding the AMDGPU_GTT_MAX_TRANSFER_SIZE value to 512,
what do you think about doing something like the change below?
This should work across all architectures and page sizes, so
AMDGPU_GTT_MAX_TRANSFER_SIZE will always correspond to the PMD
size on all architectures and with all page sizes.
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
index 0be2728aa872..c594ed7dff18 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
@@ -37,7 +37,7 @@
#define AMDGPU_PL_MMIO_REMAP (TTM_PL_PRIV + 5)
#define __AMDGPU_PL_NUM (TTM_PL_PRIV + 6)
-#define AMDGPU_GTT_MAX_TRANSFER_SIZE 512
+#define AMDGPU_GTT_MAX_TRANSFER_SIZE 1 << (PMD_SHIFT - PAGE_SHIFT)
#define AMDGPU_GTT_NUM_TRANSFER_WINDOWS
Could you please provide your thoughts on above? Is it looking ok to you?
If this looks good - here is what we were thinking:
Patches 1-4 are required to fix initial non-4k pagesize support to AMD GPU.
And since these patches are looking in good shape (since Philip has already
reviewed [1-3])- We thought it will be good to split the patch series into two.
I will send a v2 of Part-1 with patches [1-4] (will also address the review
comments
in v2 for Patch-1 & 2 from Philip) and for the rest of the patches [5-8]
Part-2, we
can continue the discussion till other things are sorted. That will also allow
us to
get these initial fixes in Part-1 ready before the 6.20 merge window.
Thoughts?
Regards,
Christian.
Signed-off-by: Donet Tom<[email protected]>
Signed-off-by: Ritesh Harjani (IBM)<[email protected]>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
index 0be2728aa872..9d038feb25b0 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
@@ -37,7 +37,7 @@
#define AMDGPU_PL_MMIO_REMAP (TTM_PL_PRIV + 5)
#define __AMDGPU_PL_NUM (TTM_PL_PRIV + 6)
-#define AMDGPU_GTT_MAX_TRANSFER_SIZE 512
+#define AMDGPU_GTT_MAX_TRANSFER_SIZE (512 / AMDGPU_GPU_PAGES_IN_CPU_PAGE)
#define AMDGPU_GTT_NUM_TRANSFER_WINDOWS 2
extern const struct attribute_group amdgpu_vram_mgr_attr_group;
