Re: [PATCH v5 2/4] dma-buf: add optional get_tph() callback
From: Christian König <christian.koenig@amd.com>
Date: 2026-05-27 06:57:54
Also in:
dri-devel, kvm, linux-pci, linux-rdma
On 5/26/26 16:43, Zhiping Zhang wrote:
quoted hunk
[Sie erhalten nicht häufig E-Mails von zhipingz@meta.com. Weitere Informationen, warum dies wichtig ist, finden Sie unter https://aka.ms/LearnAboutSenderIdentification ] 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 <redacted> --- 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