Re: [PATCH v2 2/3] drm/amdgpu/dma-buf: Add helpers to map/unmap BAR I/O with dma_map_resource()

["Christian König" <christian.koenig@amd.com>]

Please squash that together with patch #3 in this series.

On 12.09.25 13:11, Srinivasan Shanmugam wrote:
> Add helpers to map/unmap a hardware MMIO register window (PCI BAR) as a
> 1-entry sg_table using dma_map_resource()/dma_unmap_resource(). This
> will be used by MMIO_REMAP.
> 
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 51 +++++++++++++++++++++
>  1 file changed, 51 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> index ff98c87b2e0b..33fa17a927ce 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> @@ -37,11 +37,15 @@
>  #include "amdgpu_dma_buf.h"
>  #include "amdgpu_xgmi.h"
>  #include "amdgpu_vm.h"
> +#include "amdgpu_object.h"
>  #include <drm/amdgpu_drm.h>
>  #include <drm/ttm/ttm_tt.h>
>  #include <linux/dma-buf.h>
>  #include <linux/dma-fence-array.h>
>  #include <linux/pci-p2pdma.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/scatterlist.h>
> +#include <linux/slab.h>
>  
>  static const struct dma_buf_attach_ops amdgpu_dma_buf_attach_ops;
>  
> @@ -146,6 +150,53 @@ static void amdgpu_dma_buf_unpin(struct dma_buf_attachment *attach)
>  	amdgpu_bo_unpin(bo);
>  }
>  
> +/* Map a BAR-backed I/O span as a 1-entry sg_table via dma_map_resource(). */
> +static __maybe_unused struct sg_table *
> +amdgpu_dmabuf_map_iomem(struct device *dev, resource_size_t phys,
> +			size_t size, enum dma_data_direction dir)
> +{
> +	struct sg_table *sgt;
> +	unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC; /* no P2PDMA attr */
> +	dma_addr_t dma;
> +
> +	sgt = kzalloc(sizeof(*sgt), GFP_KERNEL);
> +	if (!sgt)
> +		return ERR_PTR(-ENOMEM);
> +
> +	if (sg_alloc_table(sgt, 1, GFP_KERNEL)) {
> +		kfree(sgt);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	/* No struct page backing for I/O regions. */
> +	sg_set_page(sgt->sgl, NULL, size, 0);
> +
> +	dma = dma_map_resource(dev, phys, size, dir, attrs);
> +	if (dma_mapping_error(dev, dma)) {
> +		sg_free_table(sgt);
> +		kfree(sgt);
> +		return ERR_PTR(-EIO);
> +	}
> +
> +	sg_dma_address(sgt->sgl) = dma;
> +	sg_dma_len(sgt->sgl) = size;
> +	return sgt;
> +}
> +
> +static __maybe_unused void
> +amdgpu_dmabuf_unmap_iomem(struct device *dev, struct sg_table *sgt,
> +			  enum dma_data_direction dir)
> +{
> +	/* attrs must match map side; we only used SKIP_CPU_SYNC above */
> +	dma_unmap_resource(dev,
> +			   sg_dma_address(sgt->sgl),
> +			   sg_dma_len(sgt->sgl),
> +			   dir,
> +			   0);
> +	sg_free_table(sgt);
> +	kfree(sgt);
> +}
> +
>  /**
>   * amdgpu_dma_buf_map - &dma_buf_ops.map_dma_buf implementation
>   * @attach: DMA-buf attachment