Re: [RFC PATCH 1/2] dma-buf: Add support for private interconnects

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Thu, 2025-09-25 at 15:08 +0200, Thomas Hellström wrote:
> Add a function to the dma_buf_attach_ops to indicate whether the
> connection is a private interconnect. If so the function returns
> the address to an interconnect-defined structure that can be
> used for further negotiating.
> 
> Also add a field to the dma_buf_attachment that indicates whether
> a private interconnect is used by the attachment.
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  include/linux/dma-buf.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d58e329ac0e7..e7191edb2125 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -475,6 +475,19 @@ struct dma_buf_attach_ops {
>  	 * point to the new location of the DMA-buf.
>  	 */
>  	void (*move_notify)(struct dma_buf_attachment *attach);
> +
> +	/**
> +	 * @supports_interconnect: [optional] - Does the driver
> support a local interconnect?
> +	 *
> +	 * Does the importer support a private interconnect? The
> interconnect is
> +	 * identified using a unique address defined by the exporter
> and declared
> +	 * in a protocol header.

Actually we'd probably want to use something like a

struct dma_buf_interconnect {
	const char *name;
};

Here, and for globally known interconnects have them
instantiated somewhere common since there could be multiple exporters.

>  (RFC: Should this be a struct instead).
> +	 *
> +	 * Return: A pointer to the interconnect-private attach_ops
> structure if supported,
> +	 * %NULL otherwise.
> +	 */
> +	const void *(*supports_interconnect)(struct
> dma_buf_attachment *attach,
> +					     const void
> *interconnect);

And similarly for stricter type-checking the return value could be a
struct dma_buf_interconnect_attach_ops {
};

which is subclassed for each interconnect-private attach ops.

>  };
>  
>  /**
> @@ -484,6 +497,7 @@ struct dma_buf_attach_ops {
>   * @node: list of dma_buf_attachment, protected by dma_resv lock of
> the dmabuf.
>   * @peer2peer: true if the importer can handle peer resources
> without pages.
>   * @priv: exporter specific attachment data.
> + * @interconnect: Private interconnect to use if any, NULL
> otherwise.
>   * @importer_ops: importer operations for this attachment, if
> provided
>   * dma_buf_map/unmap_attachment() must be called with the dma_resv
> lock held.
>   * @importer_priv: importer specific attachment data.
> @@ -503,6 +517,7 @@ struct dma_buf_attachment {
>  	struct list_head node;
>  	bool peer2peer;
>  	const struct dma_buf_attach_ops *importer_ops;
> +	const void *interconnect;

const struct dma_buf_interconnect *interconnect;

>  	void *importer_priv;
>  	void *priv;
>  };

/Thomas