[PATCH 2/3] drm/amdgpu: Allow P2P access through XGMI

[Christian König]

Am 16.04.25 um 06:45 schrieb Felix Kuehling:
> If peer memory is accessible through XGMI, allow leaving it in VRAM
> rather than forcing its migration to GTT on DMABuf attachment.
>
> Signed-off-by: Felix Kuehling <felix.kuehling at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 31 ++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> index 9abe592968ab3..a72c17230fd37 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> @@ -43,6 +43,30 @@
>  #include <linux/dma-fence-array.h>
>  #include <linux/pci-p2pdma.h>
>  
> +static const struct dma_buf_attach_ops amdgpu_dma_buf_attach_ops;
> +
> +/**
> + * dma_buf_attach_adev - Helper to get adev of an attachment
> + *
> + * @attach: attachment
> + *
> + * Returns:
> + * A struct amdgpu_device * if the attaching device is an amdgpu device or
> + * partition, NULL otherwise.
> + */
> +static struct amdgpu_device *dma_buf_attach_adev(struct dma_buf_attachment *attach)
> +{
> +	if (attach->importer_ops == &amdgpu_dma_buf_attach_ops) {

Oh, that is rather clever. Going to keep that in mind.

> +		struct drm_gem_object *obj = attach->importer_priv;
> +		struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
> +		struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
> +
> +		return adev;

That can be simplified to just "return amdgpu_ttm_adev(bo->tbo.bdev);".

With that nit pick addressed feel free to add my rb.

Regards,
Christian.

> +	}
> +
> +	return NULL;
> +}
> +
>  /**
>   * amdgpu_dma_buf_attach - &dma_buf_ops.attach implementation
>   *
> @@ -54,11 +78,13 @@
>  static int amdgpu_dma_buf_attach(struct dma_buf *dmabuf,
>  				 struct dma_buf_attachment *attach)
>  {
> +	struct amdgpu_device *attach_adev = dma_buf_attach_adev(attach);
>  	struct drm_gem_object *obj = dmabuf->priv;
>  	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
>  	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
>  
> -	if (pci_p2pdma_distance(adev->pdev, attach->dev, false) < 0)
> +	if (!amdgpu_dmabuf_is_xgmi_accessible(attach_adev, bo) &&
> +	    pci_p2pdma_distance(adev->pdev, attach->dev, false) < 0)
>  		attach->peer2peer = false;
>  
>  	amdgpu_vm_bo_update_shared(bo);
> @@ -477,6 +503,9 @@ bool amdgpu_dmabuf_is_xgmi_accessible(struct amdgpu_device *adev,
>  	struct drm_gem_object *obj = &bo->tbo.base;
>  	struct drm_gem_object *gobj;
>  
> +	if (!adev)
> +		return false;
> +
>  	if (obj->import_attach) {
>  		struct dma_buf *dma_buf = obj->import_attach->dmabuf;
>