linux-kernel - Re: [PATCH net-next v3 0/5] net: pse-pd: pd692x0: Add permanent configuration management support

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Message-ID: <20250917141912.314ea89b@kernel.org>
Date: Wed, 17 Sep 2025 14:19:12 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Kory Maincent <kory.maincent@...tlin.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>, Andrew Lunn
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Jiri Pirko
 <jiri@...nulli.us>, Simon Horman <horms@...nel.org>, Jonathan Corbet
 <corbet@....net>, Donald Hunter <donald.hunter@...il.com>,
 kernel@...gutronix.de, Dent Project <dentproject@...uxfoundation.org>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Maxime Chevallier
 <maxime.chevallier@...tlin.com>, linux-doc@...r.kernel.org, Kyle Swenson
 <kyle.swenson@....tech>
Subject: Re: [PATCH net-next v3 0/5] net: pse-pd: pd692x0: Add permanent
 configuration management support

On Wed, 17 Sep 2025 11:46:55 +0200 Kory Maincent wrote:
> > On Mon, 15 Sep 2025 19:06:25 +0200 Kory Maincent wrote:  
> > > This patch series introduces a new devlink-conf uAPI to manage device
> > > configuration stored in non-volatile memory. This provides a standardized
> > > interface for devices that need to persist configuration changes across
> > > reboots. The uAPI is designed to be generic and can be used by any device
> > > driver that manages persistent configuration storage.
> > > 
> > > The permanent configuration allows settings to persist across device
> > > resets and power cycles, providing better control over PSE behavior
> > > in production environments.    
> > 
> > I'm still unclear on the technical justification for this.
> > "There's a tool in another project which does it this way"
> > is not usually sufficient upstream. For better or worse we
> > like to re-implement things from first principles.
> > 
> > Could you succinctly explain why "saving config" can't be implemented
> > by some user space dumping out ethtool configuration, saving it under
> > /etc, and using that config after reboot. A'la iptables-save /
> > iptables-restore?  
> 
> I think the only reason to save the config in the NVM instead of the userspace
> is to improve boot time. As Oleksij described:
> > I can confirm a field case from industrial/medical gear. Closed system,
> > several modules on SPE, PoDL for power. Requirement: power the PDs as
> > early as possible, even before Linux. The box boots faster if power-up
> > and Linux init run in parallel. In this setup the power-on state is
> > pre-designed by the product team and should not be changed by Linux at
> > runtime.  
> 
> He told me that he also had added support for switches in Barebox for the
> same reason, the boot time. I don't know if it is a reasonable reason to add it
> in Linux.

Right, subjectively I focused on the last sentence of Oleksij's reply.
I vote we leave it out for now.