netdev - Re: [Intel-wired-lan] [PATCH net-next 0/3] ethtool: Max power support

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Date: Tue, 2 Apr 2024 07:57:24 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Wojciech Drewek <wojciech.drewek@...el.com>
Cc: Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org, idosch@...dia.com,
 edumazet@...gle.com, marcin.szycik@...ux.intel.com,
 anthony.l.nguyen@...el.com, intel-wired-lan@...ts.osuosl.org,
 pabeni@...hat.com, przemyslaw.kitszel@...el.com
Subject: Re: [Intel-wired-lan] [PATCH net-next 0/3] ethtool: Max power
 support

On Tue, 2 Apr 2024 16:46:54 +0200 Andrew Lunn wrote:
> Looking at
> https://www.optcore.net/wp-content/uploads/2017/04/QSFP-MSA.pdf table
> 7 it indicates different power budget classifications. Power level 1
> is a Maximum power of 1.5W. So does your parameter represent this?  It
> is the minimum maximum power? And your other parameter is the maximum
> maximum power?
> 
> I agree with Jakub here, there needs to be documentation added
> explaining in detail what these parameters mean, and ideally,
> references to the specification.
> 
> Does
> 
> $ ethtool --set-module enp1s0f0np0 power-max-set 4000
> 
> actually talk to the SFP module and tell it the maximum power it can
> consume. So in this case, it is not the cage, but the module?
> 
> Or is it talking to some entity which is managing the overall power
> consumption of a number of cages, and asking it to allocate a maximum
> of 4W to this cage. It might return an error message saying there is
> no power budget left?
> 
> Or is it doing both?
> 
> Sorry to be picky, but at some point, somebody is going to want to
> implement this in the Linux SFP driver, and we want a consistent
> implementation cross different implementations.

Or "guessing how things work" another way of putting this would be -
please go investigate what exactly the FW will do with these values.