[PATCH v2 4/5] RDMA/mlx5: Enable P2P DMA with fallback mechanism

[Christoph Hellwig]

On Wed, Jul 23, 2025 at 12:55:22AM -0300, Jason Gunthorpe wrote:
> On Mon, Jul 21, 2025 at 12:03:41AM -0700, Christoph Hellwig wrote:
> > On Fri, Jul 18, 2025 at 02:51:11PM +0300, Yonatan Maman wrote:
> > > From: Yonatan Maman <Ymaman at Nvidia.com>
> > > 
> > > Add support for P2P for MLX5 NIC devices with automatic fallback to
> > > standard DMA when P2P mapping fails.
> > 
> > That's now how the P2P API works.  You need to check the P2P availability
> > higher up.
> 
> How do you mean?
> 
> This looks OKish to me, for ODP and HMM it has to check the P2P
> availability on a page by page basis because every single page can be
> a different origin device.
> 
> There isn't really a higher up here...

The DMA API expects the caller to already check for connectability,
why can't HMM do that like everyone else?