Re: [PATCH v8 4/4] RDMA/mlx5: get tph for p2p access when registering dma-buf mr

[Leon Romanovsky <leon@kernel.org>]

On Sun, Jun 14, 2026 at 11:59:01PM -0700, Zhiping Zhang wrote:
> Query dma-buf PCI TPH metadata when registering a dma-buf MR for
> peer-to-peer access to a PCIe endpoint and use it to program
> requester-side TPH on the outbound mkey. If the exporter has no
> metadata, fall back to the existing no-TPH path.
> 
> Use mlx5_st_alloc_index_by_tag() to translate exporter-provided
> steering tags into local ST entries when table mode is active, and add
> mlx5_st_get_index() for DMAH-backed flows that already carry an ST
> index.
> 
> For TPH-backed FRMRs, keep the extra ST-table reference tied to MR
> lifetime rather than pooled mkey lifetime. Acquire the ref before MR
> creation and release it again when the MR is returned to the pool or
> the backing mkey is destroyed, while leaving the generic FRMR pool core
> unchanged.
> 
> Import the DMA_BUF namespace for the new dma_buf_get_pci_tph() call so
> modular mlx5_ib builds link cleanly.

The commit message explains *what* the patch does, but it lacks context on
*why* the change is needed. The 'what' is mostly clear from reading the code;
the important part missing here is the rationale behind the change.

Thanks