linux-kernel - Re: [PATCH net-next v6 06/12] net: pse-pd: Add support for budget evaluation strategies

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Message-ID: <20250325162534.313bc066@kmaincent-XPS-13-7390>
Date: Tue, 25 Mar 2025 16:25:34 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Kyle Swenson <kyle.swenson@....tech>, Andrew Lunn <andrew@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Jonathan Corbet <corbet@....net>, Donald Hunter
 <donald.hunter@...il.com>, Rob Herring <robh@...nel.org>, Andrew Lunn
 <andrew+netdev@...n.ch>, Simon Horman <horms@...nel.org>, Heiner Kallweit
 <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Liam
 Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, Thomas
 Petazzoni <thomas.petazzoni@...tlin.com>, "netdev@...r.kernel.org"
 <netdev@...r.kernel.org>, "linux-doc@...r.kernel.org"
 <linux-doc@...r.kernel.org>, Dent Project
 <dentproject@...uxfoundation.org>, "kernel@...gutronix.de"
 <kernel@...gutronix.de>, Maxime Chevallier <maxime.chevallier@...tlin.com>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v6 06/12] net: pse-pd: Add support for budget
 evaluation strategies

On Tue, 25 Mar 2025 06:34:17 +0100
Oleksij Rempel <o.rempel@...gutronix.de> wrote:

> Hi,
> 
> On Mon, Mar 24, 2025 at 05:33:18PM +0000, Kyle Swenson wrote:
> > Hello Kory,
> > 
> > On Mon, Mar 24, 2025 at 05:39:07PM +0100, Kory Maincent wrote:  
> > > Hello Kyle, Oleksij,  
> > ...  
> > > 
> > > Small question on PSE core behavior for PoE users.
> > > 
> > > If we want to enable a port but we can't due to over budget.
> > > Should we :
> > > - Report an error (or not) and save the enable action from userspace. On
> > > that case, if enough budget is available later due to priority change or
> > > port disconnected the PSE core will try automatically to re enable the
> > > PoE port. The port will then be enabled without any action from the user.
> > > - Report an error but do nothing. The user will need to rerun the enable
> > >   command later to try to enable the port again.
> > > 
> > > How is it currently managed in PoE poprietary userspace tools?  
> > 
> > So in our implementation, we're using the first option you've presented.
> > That is, we save the enable action from the user and if we can't power
> > the device due to insufficient budget remaining, we'll indicate that status
> > to the user.  If enough power budget becomes available later, we'll power up
> > the device automatically.  
> 
> It seems to be similar to administrative UP state - "ip link set dev lan1 up".
> I'm ok with this behavior.

Ack I will go for it then, thank you!

Other question to both of you:
If we configure manually the current limit for a port. Then we plug a Powered
Device and we detect (during the classification) a smaller current limit
supported. Should we change the current limit to the one detected. On that case
we should not let the user set a power limit greater than the one detected after
the PD has been plugged.

What do you think? Could we let a user burn a PD?

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