linux-kernel - Re: [PATCH net-next v2 4/4] net: pse-pd: pd692x0: Add devlink interface for configuration save/reset

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Message-ID: <aLfp5H5CTa24wA7H@pengutronix.de>
Date: Wed, 3 Sep 2025 09:10:28 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Kory Maincent <kory.maincent@...tlin.com>,
	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>, 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
Subject: Re: [PATCH net-next v2 4/4] net: pse-pd: pd692x0: Add devlink
 interface for configuration save/reset

On Tue, Sep 02, 2025 at 01:48:44PM -0700, Jakub Kicinski wrote:
> On Tue, 2 Sep 2025 13:42:12 -0700 Jakub Kicinski wrote:
> > On Tue, 2 Sep 2025 16:43:14 +0200 Kory Maincent wrote:
> > > > Sorry for not offering a clear alternative, but I'm not aware of any
> > > > precedent for treating devlink params as action triggers. devlink params
> > > > should be values that can be set and read, which is clearly not
> > > > the case here:    
> > > 
> > > Ok.
> > > We could save the configuration for every config change and add a reset-conf
> > > action to devlink reload uAPI? The drawback it that it will bring a bit of
> > > latency (about 110ms) for every config change.
> > > 
> > > Or adding a new devlink uAPI like a devlink conf but maybe we don't have enough
> > > cases to add such generic new uAPI.
> > > Or get back to the first proposition to use sysfs. 
> > > 
> > > What do you think?  
> > 
> > If you are asking for my real preference, abstracting away whether it's
> > doable and justifiable amount of effort for you -- I'd explore using
> > flags in the ethtool header to control whether setting is written to
> > the flash.
> 
> PS. failing that the less uAPI the better. Tho, given that the whole
> point here is giving user the ability to write the flash -- asking for
> uAPI-light approach feels contradictory.
> 
> Taking a step back -- the "save to flash" is something that OEM FW
> often supports. But for Linux-based control the "save to flash" should
> really be equivalent to updating some user space config. When user
> configures interfaces in OpenWRT we're not flashing them into the
> device tree... Could you perhaps explain what makes updating the
> in-flash config a high-priority requirement for PoE?
> 

I think the main use case question is: what happens if the application
CPU reboots?
Do we go back to “safe defaults”? But what are safe defaults - that can
vary a lot between systems.

In many setups, if the CPU reboots it also means the bridge is down, so
there is no packet forwarding. In that case, does it even make sense to
keep providing PoE power if the networking part is non-functional?

Another angle: does it make sense to overwrite the hardware power-on
defaults each time the system starts? Or should we rather be able to
read back the stored defaults from the hardware into the driver and work
with them?

Does anyone here have field experience with similar devices? How are
these topics usually handled outside of my bubble?

Best Regards,
Oleksij
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