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drm/amdgpu: Map/Unmap MMIO_REMAP as BAR register window; add TTM sg helpers; wire dma-buf

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MMIO_REMAP (HDP flush page) exposes a hardware MMIO register window via
a PCI BAR; there are no struct pages backing it (not normal RAM).  But
when one device shares memory with another through dma-buf, the receiver
still expects a delivery route—a list of DMA-able chunks—called an
sg_table. For the BAR window, we can’t (no pages!), so we instead create
a one-entry list that points directly to the BAR’s physical bus address
and tell DMA: “use this I/O span.” - A single, contiguous byte range on
the PCI bus (start DMA address + length)). That’s why we map it with
dma_map_resource() and set sg_set_page(..., NULL, ...). Perform DMA
reads/writes directly to that range so we build an sg_table from a BAR
physical span and map it with dma_map_resource().

This patch centralizes the BAR-I/O mapping in TTM and wires dma-buf to
it:

Add amdgpu_ttm_mmio_remap_alloc_sgt() /
amdgpu_ttm_mmio_remap_free_sgt(). They walk the TTM resource via
amdgpu_res_cursor, add the byte offset to adev->rmmio_remap.bus_addr,
build a one-entry sg_table with sg_set_page(NULL, …), and map/unmap it
with dma_map_resource().

In dma-buf map/unmap, if the BO is in AMDGPU_PL_MMIO_REMAP, call the new
helpers.

Single place for BAR-I/O handling: amdgpu_ttm.c in
amdgpu_ttm_mmio_remap_alloc_sgt() and ..._free_sgt().
No struct pages: sg_set_page(sg, NULL, cur.size, 0); inside
amdgpu_ttm_mmio_remap_alloc_sgt().
Minimal sg_table: sg_alloc_table(*sgt, 1, GFP_KERNEL); inside
amdgpu_ttm_mmio_remap_alloc_sgt().
Hooked into dma-buf: amdgpu_dma_buf_map()/unmap() in amdgpu_dma_buf.c
call these helpers for AMDGPU_PL_MMIO_REMAP.

v2: squash in fix for set/get tiling

Suggested-by: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Srinivasan Shanmugam
2025-10-06 19:46:54 +05:30
committed by Alex Deucher
parent de8955508b
commit d8c2c6c33d
5 changed files with 127 additions and 0 deletions
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18
drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
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@@ -37,6 +37,7 @@
#include "amdgpu_dma_buf.h"
#include "amdgpu_xgmi.h"
#include "amdgpu_vm.h"
#include "amdgpu_ttm.h"
#include <drm/amdgpu_drm.h>
#include <drm/ttm/ttm_tt.h>
#include <linux/dma-buf.h>
@@ -241,6 +242,14 @@ static struct sg_table *amdgpu_dma_buf_map(struct dma_buf_attachment *attach,
if (r)
return ERR_PTR(r);
break;
case AMDGPU_PL_MMIO_REMAP:
r = amdgpu_ttm_mmio_remap_alloc_sgt(adev, bo->tbo.resource,
attach->dev, dir, &sgt);
if (r)
return ERR_PTR(r);
break;
default:
return ERR_PTR(-EINVAL);
}
@@ -266,6 +275,15 @@ static void amdgpu_dma_buf_unmap(struct dma_buf_attachment *attach,
struct sg_table *sgt,
enum dma_data_direction dir)
{
struct drm_gem_object *obj = attach->dmabuf->priv;
struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
if (bo->tbo.resource &&
bo->tbo.resource->mem_type == AMDGPU_PL_MMIO_REMAP) {
amdgpu_ttm_mmio_remap_free_sgt(attach->dev, dir, sgt);
return;
}
if (sg_page(sgt->sgl)) {
dma_unmap_sgtable(attach->dev, sgt, dir, 0);
sg_free_table(sgt);