Re: [PATCH for-next] RDMA/efa: Expose device P2P DMA support via device query

[Leon Romanovsky <leon@kernel.org>]

On Wed, Oct 07, 2026 at 09:01:36AM +0000, Michael Margolin wrote:
> On Fri, Oct 02, 2026 at 11:52:41AM -0300, Jason Gunthorpe wrote:
> > On Thu, Oct 01, 2026 at 06:53:33PM +0300, Leon Romanovsky wrote:
> > 
> > > > Looked at Leon's patches and it does seem like the right place to expose
> > > > such peer relations. Although it wouldn't help with our immediate need,
> > > > maybe we can add a sysfs interface on top of Leon's patches to expose
> > > > the gathered accessiblity (and maybe also performance) information.
> > > > 
> > > > Leon, what is your opinion on this?
> > > 
> > > ACPI tables are available here /sys/firmware/acpi/tables/, this will
> > > include our new p2p HMAT extension.
> 
> I was iterating over Jason's idea and what I imagine is an interface
> that contains already parsed data at PCI level, like:
> 
> /sys/firmware/acpi/p2p/
> ├── 0000:55:00.0/          # RDMA NIC
> │   ├── 0000:59:00.0/      # → GPU (reachable peer)
> │   │   ├── latency_ns     # 200
> │   │   └── bandwidth_mbs  # 32000
> │   └── 0000:5a:00.0/      # → GPU (reachable peer)
> │       ├── latency_ns     # 200
> │       └── bandwidth_mbs  # 32000
> │
> ├── 0000:59:00.0/          # GPU
> │   ├── 0000:55:00.0/      # → RDMA NIC (reachable peer)
> │   │   ├── latency_ns     # 200
> │   │   └── bandwidth_mbs  # 32000
> │   └── 0000:56:00.0/      # → RDMA NIC (reachable peer)
> │       ├── latency_ns     # 200
> │       └── bandwidth_mbs  # 32000
> │
> ├── 0000:9a:00.0/          # NVMe
> │   └── 0000:55:00.0/      # → RDMA NIC (reachable peer)
> │       ├── latency_ns     # 300
> │       └── bandwidth_mbs  # 12000

I'm afraid that writing and maintaining an in-kernel parser that creates a matrix of
non-racy symlinks to point to right PCI BDF will be quite painful.

Thanks