linux-kernel - Re: [PATCH net-next v2 3/3] net: pse-pd: pd692x0: Preserve PSE configuration across reboots

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Message-ID: <20251014115659.0e6fd10c@kmaincent-XPS-13-7390>
Date: Tue, 14 Oct 2025 11:56:59 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Simon Horman <horms@...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>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 kernel@...gutronix.de, Dent Project <dentproject@...uxfoundation.org>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 3/3] net: pse-pd: pd692x0: Preserve PSE
 configuration across reboots

On Tue, 14 Oct 2025 09:58:56 +0100
Simon Horman <horms@...nel.org> wrote:

> On Mon, Oct 13, 2025 at 04:05:33PM +0200, Kory Maincent wrote:
> > From: Kory Maincent (Dent Project) <kory.maincent@...tlin.com>
> > 
> > Detect when PSE hardware is already configured (user byte == 42) and
> > skip hardware initialization to prevent power interruption to connected
> > devices during system reboots.
> > 
> > Previously, the driver would always reconfigure the PSE hardware on
> > probe, causing a port matrix reflash that resulted in temporary power
> > loss to all connected devices. This change maintains power continuity
> > by preserving existing configuration when the PSE has been previously
> > initialized.
> > 
> > Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>  
> 
> Hi Kory,
> 
> Perhaps I'm over thinking things here. But I'm wondering
> what provision there is for a situation whereby:
> 
> 1. The driver configures the device
> 2. A reboot occurs
> 2. The (updated) driver wants to (re)configure the device
>    with a different configuration, say because it turns
>    out there was a bug in or enhancement to the procedure at 1.
> 
> ...

You have to find a way to turn off the power supply of the PSE controller.
As adding a devlink uAPI for this was not accepted, a hard reset for the
PSE controller is the only way to clean the user byte register and (re)configure
the controller at boot time.

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