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

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Message-ID: <20250922110220.4909e58b@kernel.org>
Date: Mon, 22 Sep 2025 11:02:20 -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>, Luka Perkov <luka.perkov@...tura.hr>, Robert Marko
 <robert.marko@...tura.hr>, Sridhar Rao <srao@...uxfoundation.org>
Subject: Re: [PATCH net-next v3 0/5] net: pse-pd: pd692x0: Add permanent
 configuration management support

On Mon, 22 Sep 2025 18:20:02 +0200 Kory Maincent wrote:
> > > I think the only reason to save the config in the NVM instead of the
> > > userspace is to improve boot time. As Oleksij described:    
> > > 
> > > 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.  
> 
> I would like to restart the discussion as I have one more argument besides the
> boot time optimization coming from Luka Perkov in CC.
> 
> According to him, not having this feature supported also brings an issue across
> reboot:
> "When a network switch reboots, any devices receiving Power over
> Ethernet (PoE) from that switch will lose power unless the PoE
> configuration is persisted across the reboot cycle. This creates a
> significant operational impact: WiFi access points and other
> PoE-powered devices will experience an unplanned hard power loss,
> forcing them offline without any opportunity for graceful shutdown.
> 
> The critical issue is not the impact on the switch itself, but rather
> the cascading effect on all dependent infrastructure. Without
> kernel-level persistence of PoE settings, a simple switch reboot
> (whether for maintenance, updates, or recovery) forces all connected
> PoE devices into an abrupt power cycle. This results in extended
> downtime as these devices must complete their full boot sequence once
> power is restored, rather than remaining operational throughout the
> switch's reboot process."

Any sort of hot reset that maintains the pre-existing configuration 
and doesn't issue resets is orthogonal to storing the configuration
into the flash.