Re: [PATCH net] net: Allow non parent devices to be used for ZC DMA

[Jakub Kicinski <kuba@kernel.org>]

On Wed, 9 Jul 2025 15:56:16 -0700 Mina Almasry wrote:
> > > nit: This doesn't seem like a fix? The current code supports all
> > > devices that are not SF well enough, right? And in the case of SF
> > > devices, I expect net_devmem_bind_dmabuf() to fail gracefully as the
> > > dma mapping of a device that doesn't support it, I think, would fail
> > > gracefully. So to me this seems like an improvement rather than a bug
> > > fix.
> > >  
> > dma_buf_map_attachment_unlocked() will return a sg_table with 0 nents.
> > That is graceful. However this will result in page_pools that will
> > always be returning errors further down the line which is very confusing
> > regarding the motives that caused it.
> >
> > I am also fine to not make it a fix btw. Especially since the mlx5
> > devmem code was just accepted.
> 
> If you submit another version I'd rather it be a non-fix, especially
> since applying the io_uring hunk will be challenging when backporting
> this patch, but I assume hunk can be dropped while backporting, so I'm
> fine either way.

+1 for non-fix. The core is working as expected, if we want a Fixes tag
I'd aim it at mlx5 and make the patch reject queue binding to SFs
_within mlx5_ until the core bits are figured out.