netdev - Re: [PATCH net-next 1/2] mlxsw: Register physical ports as a devlink resource

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Date:   Wed, 13 Jan 2021 10:46:50 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
        davem@...emloft.net, jiri@...dia.com, danieller@...dia.com,
        mlxsw@...dia.com, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 1/2] mlxsw: Register physical ports as a
 devlink resource

On Wed, 13 Jan 2021 16:26:56 +0200 Ido Schimmel wrote:
> On Wed, Jan 13, 2021 at 02:39:02PM +0100, Jiri Pirko wrote:
> > Wed, Jan 13, 2021 at 09:32:41AM CET, idosch@...sch.org wrote:  
> > >On Tue, Jan 12, 2021 at 08:21:22PM -0800, Jakub Kicinski wrote:  
> > >> On Tue, 12 Jan 2021 10:39:30 +0200 Ido Schimmel wrote:  
> > >> > From: Danielle Ratson <danieller@...dia.com>
> > >> > 
> > >> > The switch ASIC has a limited capacity of physical ('flavour physical'
> > >> > in devlink terminology) ports that it can support. While each system is
> > >> > brought up with a different number of ports, this number can be
> > >> > increased via splitting up to the ASIC's limit.
> > >> > 
> > >> > Expose physical ports as a devlink resource so that user space will have
> > >> > visibility to the maximum number of ports that can be supported and the
> > >> > current occupancy.  
> > >> 
> > >> Any thoughts on making this a "generic" resource?  
> > >
> > >It might be possible to allow drivers to pass the maximum number of
> > >physical ports to devlink during their initialization. Devlink can then
> > >use it as an indication to register the resource itself instead of the
> > >driver. It can report the current occupancy without driver intervention
> > >since the list of ports is maintained in devlink.
> > >
> > >There might be an issue with the resource identifier which is a 64-bit
> > >number passed from drivers. I think we can partition this to identifiers
> > >allocated by devlink / drivers.
> > >
> > >Danielle / Jiri?  
> > 
> > There is no concept of "generic resource". And I think it is a good
> > reason for it, as the resource is something which is always quite
> > hw-specific. Port number migth be one exception. Can you think of
> > anything else? If not, I would vote for not having "generic resource"
> > just for this one case.  
> 
> I think Jakub's point is that he does not want drivers to expose the
> same resource to user space under different names.

Exactly.

> Question is how to
> try to guarantee it. One option is what I suggested above, but it might
> be an overkill. Another option is better documentation. To add a section
> of "generic" resources in devlink-resource documentation [1] and modify
> the kernel-doc comment above devlink_resource_register() to point to it.
> 
> [1] https://www.kernel.org/doc/html/latest/networking/devlink/devlink-resource.html

Yup, an entry in documentation and a common define in net/devlink.h
is fine by me. We can always move around the kernel internals, like 
what registers the resource, later.