netdev - Re: [PATCH net-next 08/12] net: pse-pd: pd692x0: Add support for PSE PI priority feature

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Message-ID: <20241008162120.18aa0a6c@kmaincent-XPS-13-7390>
Date: Tue, 8 Oct 2024 16:21:20 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: 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>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 linux-doc@...r.kernel.org, Kyle Swenson <kyle.swenson@....tech>, Dent
 Project <dentproject@...uxfoundation.org>, kernel@...gutronix.de
Subject: Re: [PATCH net-next 08/12] net: pse-pd: pd692x0: Add support for
 PSE PI priority feature

On Tue, 8 Oct 2024 15:57:22 +0200
Oleksij Rempel <o.rempel@...gutronix.de> wrote:

> On Thu, Oct 03, 2024 at 01:41:02AM +0200, Andrew Lunn wrote:
> > > +	msg = pd692x0_msg_template_list[PD692X0_MSG_SET_PORT_PARAM];
> > > +	msg.sub[2] = id;
> > > +	/* Controller priority from 1 to 3 */
> > > +	msg.data[4] = prio + 1;  
> > 
> > Does 0 have a meaning? It just seems an odd design if it does not.  
> 
> 0 is not documented. But there are sub-priority which are not directly
> configured by user, but affect the system behavior.
> 
> Priority#: Critical – 1; high – 2; low – 3
>  For ports with the same priority, the PoE Controller sets the
>  sub-priority according to the logic port number. (Lower number gets
>  higher priority).
> 
> Port priority affects:
> 1. Power-up order: After a reset, the ports are powered up according to
>  their priority, highest to lowest, highest priority will power up first.
> 2. Shutdown order: When exceeding the power budget, lowest priority
>  ports will turn off first.
> 
> Should we return sub priorities on the prio get request?
> 
> If i see it correctly, even if user do not actively configures priorities,
> they are always present. For example port 0 will have always a Prio
> higher than Port 10.

We could add a subprio ehtool attribute, but it won't be configurable.
In fact it could be configurable by changing the port matrix order but it is not
a good idea. Applying a new port matrix turn off all the ports.

I am not sure if it is specific to Microchip controller or if it is generic
enough to add the attribute.
I would say not to return it for now.

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