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

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Message-ID: <20250917114655.6ed579eb@kmaincent-XPS-13-7390>
Date: Wed, 17 Sep 2025 11:46:55 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Jakub Kicinski <kuba@...nel.org>
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 Tue, 16 Sep 2025 16:54:40 -0700
Jakub Kicinski <kuba@...nel.org> 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.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com