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

[Ratheesh Kannoth]

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'll update the commit message to make this hardware constraint
explicit: the single-instance guard is not a software limitation but a
direct reflection of the RVU architecture, where one AF device manages
all RVU functional blocks for the entire system.