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

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Message-ID: <7b0b3d27-c21d-4765-875b-2dd4681a2ba4@lunn.ch>
Date: Wed, 3 Apr 2024 15:40:07 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Wojciech Drewek <wojciech.drewek@...el.com>
Cc: netdev@...r.kernel.org, idosch@...dia.com, edumazet@...gle.com,
	marcin.szycik@...ux.intel.com, anthony.l.nguyen@...el.com,
	kuba@...nel.org, 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 Wed, Apr 03, 2024 at 03:18:44PM +0200, Wojciech Drewek wrote:
> 
> 
> On 02.04.2024 16:46, Andrew Lunn wrote:
> > On Tue, Apr 02, 2024 at 01:38:59PM +0200, Wojciech Drewek wrote:
> >>
> >>
> >> On 30.03.2024 22:57, Andrew Lunn wrote:
> >>> On Fri, Mar 29, 2024 at 10:23:18AM +0100, Wojciech Drewek wrote:
> >>>> Some ethernet modules use nonstandard power levels [1]. Extend ethtool
> >>>> module implementation to support new attributes that will allow user
> >>>> to change maximum power. Rename structures and functions to be more
> >>>> generic. Introduce an example of the new API in ice driver.
> >>>>
> >>>> Ethtool examples:
> >>>> $ ethtool --show-module enp1s0f0np0
> >>>> Module parameters for enp1s0f0np0:
> >>>> power-min-allowed: 1000 mW
> >>>> power-max-allowed: 3000 mW
> >>>> power-max-set: 1500 mW
> >>>>
> >>>> $ ethtool --set-module enp1s0f0np0 power-max-set 4000
> >>>
> >>> We have had a device tree property for a long time:
> >>>
> >>>   maximum-power-milliwatt:
> >>>     minimum: 1000
> >>>     default: 1000
> >>>     description:
> >>>       Maximum module power consumption Specifies the maximum power consumption
> >>>       allowable by a module in the slot, in milli-Watts. Presently, modules can
> >>>       be up to 1W, 1.5W or 2W.
> >>>
> >>> Could you flip the name around to be consistent with DT?
> >>
> >> Yea, I'm open to any name suggestion although I don't like the unit in the parameter name :) 
> > 
> > That is a DT thing. Helps make the units of an ABI obvious. However,
> > milliwatts is pretty standard with the kernel of user APIs, e.g. all
> > hwmon calls use milliwatts.
> > 
> >>>> minimum-power-allowed: 1000 mW
> >>>> maximum-power-allowed: 3000 mW
> >>>> maximum-power-set: 1500 mW
> >>>
> >>> Also, what does minimum-power-allowed actually tell us? Do you imagine
> >>> it will ever be below 1W because of bad board design? Do you have a
> >>> bad board design which does not allow 1W?
> >>
> >> Yes. in case of QSFP we don't support 1W, 1.5W is the minimum.
> > 
> > So if i plug in a 1W QSFP device, it will let the magic smoke out
> > because it is force fed 1.5W?
> > 
> > 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?
> 
> Exactly as you described, minimum-power-allowed is in fact minimum value
> which maximum-power-set can be set to (so minimum maximum). the other
> parameter is maximim maximum.

Table 7 in that document is titled "Power Budget Classification". So
how about

minimum-power-class-allowed: 1000 mW
maximum-power-class-allowed: 3000 mW

	Andrew