Re: [PATCH] powerpc/powernv/pci: Drop VF MPS fixup

["Oliver O'Halloran" <oohall@gmail.com>]

On Thu, May 19, 2022 at 10:38 PM Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> > Le 02/09/2020 à 05:51, Oliver O'Halloran a écrit :
> >> The MPS field in the VF config space is marked as reserved in current
> >> versions of the SR-IOV spec. In other words, this fixup doesn't do
> >> anything.
> >>
> >> Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
> >
> > A lot of cleanup patches from Oliver were merged in Septembre 2020 but
> > not this one.
> >
> > Any reason ?
>
> It wasn't clear to me that it's safe to remove. The commit that added it
> seemed to think it was important.
>
> The fact that it's out-of-spec doesn't mean we don't have some hardware
> somewhere that relies on that.

There is no hardware that depends on it. It was added in response to a
bug report on the IBM internal bugzilla about virtual functions not
reporting the same MPS as the physical function in the output of
lspci. This is by design since MPS is a property that is only relevant
to the PF. There was a corresponding patch to skiboot to intercept
writes to the MPS field of VFs which was used to fake a writable MPS
field in firmware. I removed that hack in 2019
(https://github.com/open-power/skiboot/commit/22057f868f3b2b1fd02647a738f6da0858b5eb6c)
since it was pointless and was causing other problems. There's no real
reason to keep this code around IMO.