On 7/1/26 00:42, Zhiping Zhang wrote:
> Add an optional dma_buf_ops.get_pci_tph callback and a
> DMA-buf importer wrapper, dma_buf_get_pci_tph().
>
> TPH is PCIe TLP Processing Hint. 8-bit ST and 16-bit Extended ST are
> distinct PCIe TPH namespaces, so the importer requests the namespace it
> can emit and the exporter returns the matching ST/PH tuple or
> -EOPNOTSUPP.
>
> dma_buf_get_pci_tph() is the importer entry point. It requires
> &dmabuf->resv to be held while the callback runs and returns
> -EOPNOTSUPP when the exporter does not provide PCI TPH metadata.
>
> The first user is VFIO_DEVICE_FEATURE_DMA_BUF_TPH in vfio-pci, with
> mlx5 as the first importer.
>
> Signed-off-by: Zhiping Zhang <[email protected]>
> ---
> drivers/dma-buf/dma-buf.c | 25 +++++++++++++++++++++++++
> include/linux/dma-buf.h | 22 ++++++++++++++++++++++
> 2 files changed, 47 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index d504c636dc29..7a4c9b0d5dab 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -1144,6 +1144,31 @@ void dma_buf_unpin(struct dma_buf_attachment *attach)
> }
> EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, "DMA_BUF");
>
> +/**
> + * dma_buf_get_pci_tph - Retrieve PCIe TLP Processing Hint (TPH) metadata
> + * @dmabuf: DMA buffer to query
> + * @extended: false for 8-bit ST, true for 16-bit Extended ST
> + * @steering_tag: returns the raw steering tag for the requested namespace
> + * @ph: returns the TPH processing hint
> + *
> + * Wrapper for the optional &dma_buf_ops.get_pci_tph callback.
> + *
> + * Must be called with &dma_buf.resv held. Returns -EOPNOTSUPP if the
> + * exporter does not implement the callback or has no metadata for the
> + * requested namespace.
Please add something like this:
* The returned information is only valid till the next invalidate_mappings()
callback from the exporter and should be re-queried when a new mapping is
created after invalidation.
Apart from that it looks good to me, but I still think we need some kind of
example that this works for other DMA-buf users as well.
Just demonstrating that this also works with some simple FPGA or similar PCIe
endpoint should be sufficient.
Regards,
Christian.
> + */
> +int dma_buf_get_pci_tph(struct dma_buf *dmabuf, bool extended,
> + u16 *steering_tag, u8 *ph)
> +{
> + dma_resv_assert_held(dmabuf->resv);
> +
> + if (!dmabuf->ops->get_pci_tph)
> + return -EOPNOTSUPP;
> +
> + return dmabuf->ops->get_pci_tph(dmabuf, extended, steering_tag, ph);
> +}
> +EXPORT_SYMBOL_NS_GPL(dma_buf_get_pci_tph, "DMA_BUF");
> +
> /**
> * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
> * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index d1203da56fc5..53b2686ad8fc 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -113,6 +113,26 @@ struct dma_buf_ops {
> */
> void (*unpin)(struct dma_buf_attachment *attach);
>
> + /**
> + * @get_pci_tph:
> + *
> + * Retrieve PCIe TLP Processing Hint (TPH) steering metadata for
> + * this buffer so an importer can program a matching ST/PH hint on
> + * outbound TLPs targeting the exporter for peer-to-peer DMA.
> + *
> + * @dmabuf: DMA buffer for which to retrieve TPH metadata
> + * @extended: false for 8-bit ST, true for 16-bit Extended ST
> + * @steering_tag: Returns the raw TPH steering tag for the requested
> + * namespace
> + * @ph: Returns the TPH processing hint (2-bit value)
> + *
> + * Optional callback for dma_buf_get_pci_tph(). Called with
> + * &dma_buf.resv held. Returns 0 on success or -EOPNOTSUPP when
> + * the exporter has no metadata for the requested namespace.
> + */
> + int (*get_pci_tph)(struct dma_buf *dmabuf, bool extended,
> + u16 *steering_tag, u8 *ph);
> +
> /**
> * @map_dma_buf:
> *
> @@ -563,6 +583,8 @@ void dma_buf_detach(struct dma_buf *dmabuf,
> struct dma_buf_attachment *attach);
> int dma_buf_pin(struct dma_buf_attachment *attach);
> void dma_buf_unpin(struct dma_buf_attachment *attach);
> +int dma_buf_get_pci_tph(struct dma_buf *dmabuf, bool extended,
> + u16 *steering_tag, u8 *ph);
>
> struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);
>
