linux-kernel - Re: [PATCH net-next v5 06/12] net: pse-pd: Add support for budget evaluation strategies

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Message-ID: <Z76t0VotFL7ji41M@pengutronix.de>
Date: Wed, 26 Feb 2025 06:59:45 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Kory Maincent <kory.maincent@...tlin.com>, Andrew Lunn <andrew@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, 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>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	netdev@...r.kernel.org, linux-doc@...r.kernel.org,
	Kyle Swenson <kyle.swenson@....tech>,
	Dent Project <dentproject@...uxfoundation.org>,
	kernel@...gutronix.de,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 06/12] net: pse-pd: Add support for budget
 evaluation strategies

On Tue, Feb 25, 2025 at 05:47:52PM -0800, Jakub Kicinski wrote:
> On Tue, 25 Feb 2025 10:25:58 +0100 Kory Maincent wrote:
> > On Mon, 24 Feb 2025 13:45:22 -0800
> > Jakub Kicinski <kuba@...nel.org> wrote:
> > 
> > > > No they can't for now. Even different PSE power domains within the same PSE
> > > > controller. I will make it explicit.    
> > > 
> > > Sounds like the property is placed at the wrong level of the hierarchy,
> > > then.  
> > 
> > When a PSE controller appears to be able to support mixed budget strategy and
> > could switch between them it will be better to have it set at the PSE power
> > domain level. As the budget is per PSE power domain, its strategy should also
> > be per PSE power domain.
> > For now, it is simply not configurable and can't be mixed. It is hard-coded by
> > the PSE driver.
> 
> Yes, but uAPI is forever. We will have to live with those domain
> attributes duplicated on each port. Presumably these port attributes
> will never support a SET operation, since the set should be towards 
> the domain? The uAPI does not inspire confidence. If we need more
> drivers to define a common API maybe a local sysfs API in the driver
> will do?

I tend to disagree here. The evaluation/allocation methods should be
per port.  

At this step, we support only "hardware"(firmware)-based methods:  
1. Static – Plain hardware classification-based power allocation per
port.  
2. Dynamic – Hardware classification with constant measurement for
optimization.  

For some devices, the dynamic method may not work reliably enough,
so we will need to switch to a fixed allocation method, which is
currently not implemented but will be set via user space. This
should be configurable per port.  

At some point, we will need to introduce LLDP-based allocation from
user space. This will be managed by a daemon.

For testing, here’s an example of how LLDP-based power negotiation can
be analyzed:
https://telecomtest.com.au/wp-content/uploads/2016/12/PDA-LLDP-Powered-Device-LLDP-Analyzer.pdf

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