Re: [PATCH net] net: eth: fbnic: Fix addr validation in pcs write

[Mike Marciniszyn <mike.marciniszyn@gmail.com>]

On Sat, May 02, 2026 at 04:02:04PM +0200, Andrew Lunn wrote:
> On Sat, May 02, 2026 at 05:45:08AM -0400, Mike Marciniszyn wrote:
> > On Fri, May 01, 2026 at 02:46:36PM +0100, Simon Horman wrote:
> > > On Wed, Apr 29, 2026 at 11:00:49AM -0400, mike.marciniszyn@gmail.com wrote:
> > > > From: "Mike Marciniszyn (Meta)" <mike.marciniszyn@gmail.com>
> > > >
> > > > This patch contains a fix for addr validation in fbnic_mdio_write_pcs().
> > >
> > > Hi Mike,
> > >
> > > I think this warrants a bit more explanation: Why should addr 2 be
> > > accepted? What happens from a user-perspective when it is not?
> > >
> >
> > The DW IP part has two distinct PCS address ranges cooresponding
> > to the C45 PCS registers.
> >
> > The shim translates the PCS mmd/addr/regno into specific CSR writes
> > to one of two zero-relative addr values into one of those two
> > ranges.
> >
> > This patch fixes a one off in the test that could allow an invalid
> > CSR write if an addr == 2 was called.
>
> Stable runs say:
>
> It must either fix a real bug that bothers people, ...
>
> Can this bug be triggered with the current driver? Are there any
> noticeable effects? How would somebody inside Meta know they need this
> fix? This should be included in the commit message.
>
>     Andrew

Thanks Andrew!

I am working inside Meta with Alex and Kuba.   I noticed the one off when
doing the patch that reworks the shim.

As to a real impact, that depends on the part2 series, but before that
series no one would care, which is why I had in as part of
the patch 1 series.

Without the follow on work, I suspect that no one cares or would
see any issue as I have yet to present the xpcs changes in part2.

Perhaps the best thing to do is beef up the commit and remove the
stable Cc, leaving the Fixes linkage?

Mike