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 <[email protected]> --- 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) + * @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
