Re: [RFC net-next v2 1/2] devlink: add whole device devlink instance

[Jacob Keller <jacob.e.keller@intel.com>]

On 2/19/2025 8:32 AM, Przemek Kitszel wrote:
> Add a support for whole device devlink instance. Intented as a entity
> over all PF devices on given physical device.
> 
> In case of ice driver we have multiple PF devices (with their devlink
> dev representation), that have separate drivers loaded. However those
> still do share lots of resources due to being the on same HW. Examples
> include PTP clock and RSS LUT. Historically such stuff was assigned to
> PF0, but that was both not clear and not working well. Now such stuff
> is moved to be covered into struct ice_adapter, there is just one instance
> of such per HW.
> 
> This patch adds a devlink instance that corresponds to that ice_adapter,
> to allow arbitrage over resources (as RSS LUT) via it (further in the
> series (RFC NOTE: stripped out so far)).
> 
> Thanks to Wojciech Drewek for very nice naming of the devlink instance:
> PF0:		pci/0000:00:18.0
> whole-dev:	pci/0000:00:18
> But I made this a param for now (driver is free to pass just "whole-dev").
> 
> $ devlink dev # (Interesting part of output only)
> pci/0000:af:00:
>   nested_devlink:
>     pci/0000:af:00.0
>     pci/0000:af:00.1
>     pci/0000:af:00.2
>     pci/0000:af:00.3
>     pci/0000:af:00.4
>     pci/0000:af:00.5
>     pci/0000:af:00.6
>     pci/0000:af:00.7
> 

This adds an additional devlink interface instead of replacing the
existing scheme? Seems reasonable to avoid compatibility issues with
older driver versions. I had wanted to use a single instance pretty much
from my initial attempts at flash update, but ended up giving up at the
time.

I do like that we can see the nesting so its clear which ones are connected.

One downside to this approach is in dealing with something like direct
assignment with virtualization. In practice, I think that already exists
because of HW limitations, and I would expect most such setups want to
assign the entire device rather than just one of its functions.