On 12.09.25 13:11, Srinivasan Shanmugam wrote:
> MMIO_REMAP (HDP flush page) exposes a hardware MMIO register window via a PCI
> BAR.
>
> Handle it as fixed I/O:
> - map(): if MMIO_REMAP, require P2P, compute the BAR address (bus_addr + page
> offset), and build a 1-entry sg_table with dma_map_resource().
> - unmap(): if MMIO_REMAP, call dma_unmap_resource() and return.
>
> Cc: Christian König <[email protected]>
> Cc: Alex Deucher <[email protected]>
> Signed-off-by: Srinivasan Shanmugam <[email protected]>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 39 +++++++++++++++++++--
> 1 file changed, 37 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> index 33fa17a927ce..f85e16be438f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> @@ -151,7 +151,7 @@ static void amdgpu_dma_buf_unpin(struct
> dma_buf_attachment *attach)
> }
>
> /* Map a BAR-backed I/O span as a 1-entry sg_table via dma_map_resource(). */
> -static __maybe_unused struct sg_table *
> +static struct sg_table *
> amdgpu_dmabuf_map_iomem(struct device *dev, resource_size_t phys,
> size_t size, enum dma_data_direction dir)
> {
> @@ -183,7 +183,7 @@ amdgpu_dmabuf_map_iomem(struct device *dev,
> resource_size_t phys,
> return sgt;
> }
>
> -static __maybe_unused void
> +static void
> amdgpu_dmabuf_unmap_iomem(struct device *dev, struct sg_table *sgt,
> enum dma_data_direction dir)
> {
> @@ -218,6 +218,9 @@ static struct sg_table *amdgpu_dma_buf_map(struct
> dma_buf_attachment *attach,
> struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
> struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
> struct sg_table *sgt;
> + resource_size_t phys;
> + u64 off;
> + size_t len;
> long r;
>
> if (!bo->tbo.pin_count) {
> @@ -261,6 +264,29 @@ 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:
> + /* Only allow when importer can reach exporter via P2P. */
> + if (!attach->peer2peer ||
> + pci_p2pdma_distance(adev->pdev, attach->dev, false) < 0)
> + return ERR_PTR(-EOPNOTSUPP);
> +
> + if (!adev->rmmio_remap.bus_addr)
> + return ERR_PTR(-ENODEV);
> +
> + if (bo->tbo.base.size != AMDGPU_GPU_PAGE_SIZE)
> + return ERR_PTR(-EINVAL);
I think you can drop those checks.
> +
> + /* TTM start is in pages → convert to byte offset. */
> + off = (u64)bo->tbo.resource->start << PAGE_SHIFT;
Please don't use resource->start for that. Instead use the functions in
amdgpu_res_cursor.h.
> + len = AMDGPU_GPU_PAGE_SIZE;
> + phys = adev->rmmio_remap.bus_addr + off;
> +
> + sgt = amdgpu_dmabuf_map_iomem(attach->dev, phys, len, dir);
Move the amdgpu_dmabuf_map_iomem() function as well as the off and length
calculation into amdgpu_ttm.c.
That is still not an ideal placement, but better than here.
Apart from that looks good to me.
Regards,
Christian.
> + if (IS_ERR(sgt))
> + return sgt;
> + break;
> +
> default:
> return ERR_PTR(-EINVAL);
> }
> @@ -286,6 +312,15 @@ 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_dmabuf_unmap_iomem(attach->dev, sgt, dir);
> + return;
> + }
> +
> if (sg_page(sgt->sgl)) {
> dma_unmap_sgtable(attach->dev, sgt, dir, 0);
> sg_free_table(sgt);
