netdev - Re: [RFC 0/2] Retrieve tph from dmabuf for PCIe P2P memory access

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Message-ID: <20260209181303.GB943673@ziepe.ca>
Date: Mon, 9 Feb 2026 14:13:03 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Zhiping Zhang <zhipingz@...a.com>
Cc: Leon Romanovsky <leon@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-rdma@...r.kernel.org, linux-pci@...r.kernel.org,
	netdev@...r.kernel.org, Keith Busch <kbusch@...nel.org>,
	Yochai Cohen <yochai@...dia.com>, Yishai Hadas <yishaih@...dia.com>,
	Bjorn Helgaas <helgaas@...nel.org>
Subject: Re: [RFC 0/2] Retrieve tph from dmabuf for PCIe P2P memory access

On Mon, Feb 09, 2026 at 09:53:10AM -0800, Zhiping Zhang wrote:
> Currently, the steering tag can be used for a CPU on the motherboard; the
> ACPI check is in place to query and obtain the supported tph settings. Here
> we intend to use the tph info to improve RDMA NIC memory access on a vfio-based
> accelerator device via PCIe peer-to-peer. When an applicantion register a
> RDMA memory region with DMABUF for the RDMA NIC to access the device memory,
> the tph associated with the memory region can be retrieved and used to set the
> steering tag / process hint (ph). The tph contains additional instructions
> or hints to the GPU or accelerator device for advanced memory operations,
> such as, read cache selection.
> 
> Note this RFC is for the discussion on the direction and is not intended to be
> a complete implementation. Once the direction is agreed on, we will work on the
> implementation or a real patch set.

you didn't cc the DRM people who really need to look at any changes to
the dmabuf contract.

Jason