Re: [TECH TOPIC] UALink driver upstreaming

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Sep 12, 2025 at 09:13:23AM -0700, Matthew Brost wrote:
> On Fri, Sep 12, 2025 at 09:49:56AM -0400, Rodrigo Vivi wrote:
> > On Fri, Sep 12, 2025 at 02:18:40PM +0200, Linus Walleij wrote:
> > > On Fri, Sep 12, 2025 at 2:07 PM Konstantin Sinyuk <sinyuk@gmail.com> wrote:
> > > 
> > > > Longer term, as UAL adoption grows and multiple vendors hook into the
> > > > framework, the natural home would be a dedicated drivers/ual/, just as
> > > > CXL evolved into its own subsystem.
> > > 
> > > If you already know there will be other things than accelerators there,
> > > so it's more like, i don't know, PCI or greybus, then put it into its own
> > > subsystem in drivers/ualink from day one, I think drivers/ual is a bit
> > > terse, the world is full och TLA:s already, also that is its actual name
> > > isn't it? Hard to miss if someone is looking for it.
> > > 
> > > Your merges can still go through some submaintainer like Greg, or
> > > DRM, if they need some shepherding to start out. After all that's how
> > > drivers/accel is managed, through DRM.
> > 
> > I agree it should be drivers/ualink from day 1.
> > 
> > I like the idea of the flow through drm.
> > 
> 
> +1 to both. I like the idea of creating a mini subsystem for ualink,
> going through DRM. With that, let's include dri-devel on all future
> ualink discussions.

Something like ualink has a lot less to do with DRM than it does with
networking and RDMA. These things are not "CPU buses" like PCI, they
are full multi-host network fabrics with switches, network addressing,
fabric management, and so on.

IMHO what principally distinguishes ualink from something like
classical RDMA is the expectation that the RMAs are triggered directly
in accelerator HW through load/store operations, and not from some
userspace CPU application in Linux.

But I would still expect to see the usual range of networky UAPIs
around link state, phy debugging, telemetry and general management
operations.

A normal subsystem seems like the right thing, but don't flow it
through DRM, just send it to Linus.

I think my main ask would be to have an intree user driver before
sending anything. Too much of this space relies on out of tree
accelerator drivers :(

Jason