Re: [PATCH v19 net-next 1/9] octeontx2-af: Enforce single RVU AF probe

[Ratheesh Kannoth]

On 2026-06-09 at 07:32:49, Jakub Kicinski (kuba@xxxxxxxxxx) wrote:
> On Tue, 9 Jun 2026 07:13:40 +0530 Ratheesh Kannoth wrote:
> > On 2026-06-09 at 04:10:14, Jakub Kicinski (kuba@xxxxxxxxxx) wrote:
> > > On Fri, 5 Jun 2026 12:02:37 +0530 Ratheesh Kannoth wrote:
> > > > There is only one admin-function PCI device per system.
> > > > Reject any additional AF probe with -EBUSY so the driver model matches
> > > > hardware and automated reviewers can rely on a single bound instance.
> > >
> > > Could you point me to a PCI networking driver written in the last two
> > > decades which would have this sort of limitation?
> > >
> > > At the very least you need to explain in the commit message **why**
> > > correctly handling multiple devices in a system is beyond your
> > > abilities.
> >
> > The comparison to a generic PCI networking driver isn't quite applicable
> > here. The RVU AF (Administrative Function) is not a standard NIC PF —
> > it is a system-level resource manager that owns a single, shared set of
> > AF registers across the entire RVU subsystem. The hardware spec is
> > explicit on this: "RVU has a single, common set of AF registers.
> >
> > This is fundamentally different from a multi-port NIC where each PF is
> > an independent, symmetric instance. In the RVU model, there is exactly
> > one AF device per SoC, and all other PFs  communicate with it
> > via mailboxes rather than accessing AF registers directly. Allowing a
> > second AF probe would mean two driver instances racing to manage the
> > same global hardware state — provisioning LFs, configuring
> > NPC/NIX/NPA — with no hardware arbitration between them.
>
> I asked you before - is this a driver for a PCIe devices?
> You said "yes". If so what prevents the user from plugging two such
> devices into one system?

The RVU AF (PCI device ID 0xA065) is not a pluggable add-in card. It
is an integrated function inside the Marvell OcteonTX2/CN10K/CN20K SoC.
On-chip firmware programs the PCI configuration space for all RVU
functions at boot time — setting device ID, class code, and BAR layout
via RVU_PRIV_PF()_ID_CFG — and the Linux PCI subsystem then discovers
what firmware has configured. There is no slot, no connector, and no
mechanism by which a second instance of this device could appear on the
same system. The hardware exposes exactly one AF PCI device per SoC,
and that is the only device this driver (rvu af driver) binds to.