Re: [PATCH v5 2/4] dma-buf: add optional get_tph() callback

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

On 5/26/26 16:43, Zhiping Zhang wrote:
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> 
> Add an optional dma-buf get_tph callback so an exporter can return TPH
> (TLP Processing Hints) metadata to an importer.
> 
> 8-bit ST and 16-bit Extended ST are distinct namespaces in the PCIe TPH
> ST table and may both be present with different values. The importer
> passes its supported steering-tag width and the exporter returns the
> matching value, or -EOPNOTSUPP if no metadata is available for that
> width.
> 
> The first user is VFIO_DEVICE_FEATURE_DMA_BUF_TPH in vfio-pci, with the
> mlx5 RDMA driver as the first importer.
> 
> Signed-off-by: Zhiping Zhang <zhipingz@meta.com>
> ---
>  include/linux/dma-buf.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d1203da56fc5..49eb6ad644a2 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -113,6 +113,27 @@ struct dma_buf_ops {
>          */
>         void (*unpin)(struct dma_buf_attachment *attach);
> 
> +       /**
> +        * @get_tph:
> +        * @dmabuf: DMA buffer for which to retrieve TPH metadata
> +        * @steering_tag: Returns the raw TPH steering tag for @st_width
> +        * @ph: Returns the TPH processing hint (2-bit value)

Returned values as last arguments please.

Regards,
Christian.

> +        * @st_width: Consumer's supported steering tag width in bits (8 or 16)
> +        *
> +        * Return the TPH (TLP Processing Hints) metadata associated with this
> +        * DMA buffer for the requested steering-tag width. 8-bit ST and 16-bit
> +        * Extended ST are distinct namespaces in the PCIe TPH ST table and may
> +        * both be present with different values, so the exporter must select the
> +        * value that matches @st_width and must not substitute one for the other.
> +        *
> +        * Return 0 on success, -EOPNOTSUPP if no metadata is available for the
> +        * requested width, or -EINVAL if @st_width is not 8 or 16.
> +        *
> +        * This callback is optional.
> +        */
> +       int (*get_tph)(struct dma_buf *dmabuf, u16 *steering_tag, u8 *ph,
> +                      u8 st_width);
> +
>         /**
>          * @map_dma_buf:
>          *
> --
> 2.53.0-Meta
>