netdev - Re: [PATCH net-next V4 02/14] documentation: networking: add shared devlink documentation

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Message-ID: <20251128191924.7c54c926@kernel.org>
Date: Fri, 28 Nov 2025 19:19:24 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Tariq Toukan <tariqt@...dia.com>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Donald Hunter
 <donald.hunter@...il.com>, Jonathan Corbet <corbet@....net>, Saeed Mahameed
 <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, Mark Bloch
 <mbloch@...dia.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-rdma@...r.kernel.org, Gal Pressman
 <gal@...dia.com>, Moshe Shemesh <moshe@...dia.com>, Carolina Jubran
 <cjubran@...dia.com>, Cosmin Ratiu <cratiu@...dia.com>, Jiri Pirko
 <jiri@...dia.com>, Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH net-next V4 02/14] documentation: networking: add shared
 devlink documentation

On Fri, 28 Nov 2025 12:00:13 +0100 Jiri Pirko wrote:
> >> +Shared devlink instances allow multiple physical functions (PFs) on the same
> >> +chip to share an additional devlink instance for chip-wide operations. This
> >> +should be implemented within individual drivers alongside the individual PF
> >> +devlink instances, not replacing them.
> >> +
> >> +The shared devlink instance should be backed by a faux device and should
> >> +provide a common interface for operations that affect the entire chip
> >> +rather than individual PFs.  
> >
> >If we go with this we must state very clearly that this is a crutch and
> >_not_ the recommended configuration...  
> 
> Why "not recommented". If there is a usecase for this in a dirrerent
> driver, it is probably good to utilize the shared instance, isn't it?
> Perhaps I'm missing something.

Having a single instance seems preferable from user's point of view.

> >... because presumably we could use this infra to manage a single
> >devlink instance? Which is what I asked for initially.  
> 
> I'm not sure I follow. If there is only one PF bound, there is 1:1
> relationship. Depends on how many PFs of the same ASIC you have.

I'm talking about multi-PF devices. mlx5 supports multi-PF setup for
NUMA locality IIUC. In such configurations per-PF parameters can be
configured on PCI PF ports.

> >Why can't this mutex live in the core?  
> 
> Well, the mutex protect the list of instances which are managed in the
> driver. If you want to move the mutex, I don't see how to do it without
> moving all the code related to shared devlink instances, including faux
> probe etc. Is that what you suggest?

Multiple ways you can solve it, but drivers should have to duplicate
all the instance management and locking. BTW please don't use guard().