Netdev devlink A/B firmware bank selection feature

Hi Jiri,

I'm from the FBNIC team at Meta, working on firmware and drivers. I
realized that devlink core currently lacks a feature for selecting
which A/B bank to use to activate the firmware, i.e currently we just
have "devlink dev reload pci/<bdf> action fw_activate" to activate a
pending image, or reload a current image if none is pending.

I'm thinking of adding a feature that allows for A/B bank selection,
something like:

devlink dev reload pci/<bdf> action fw_activate bank active
devlink dev reload pci/<bdf> action fw_activate bank inactive

This will be useful if say we just activated a problematic image, and
want to immediately roll back to the previous good one.

Before I submit a series, some questions:
1. Has this feature been proposed before? Were there objections or
discussions I should read?
2. Is extending fw_activate the right interface, or is there an
existing mechanism already for what I'm trying to achieve?
3. How should userspace discover bank-selection support, so explicit
selection cannot silently fall back to ordinary activation on older
kernels?

Regards,
Zinc Lim