netdev - Re: [PATCH net-next 2/3] ethtool: Introduce max power support

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Message-ID: <0cbbc736-f87c-4e58-a0a7-9c2d04e7b2cf@intel.com>
Date: Wed, 3 Apr 2024 11:50:34 +0200
From: Wojciech Drewek <wojciech.drewek@...el.com>
To: Andrew Lunn <andrew@...n.ch>
CC: <netdev@...r.kernel.org>, <intel-wired-lan@...ts.osuosl.org>,
	<anthony.l.nguyen@...el.com>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <idosch@...dia.com>, <przemyslaw.kitszel@...el.com>,
	<marcin.szycik@...ux.intel.com>
Subject: Re: [PATCH net-next 2/3] ethtool: Introduce max power support



On 30.03.2024 23:14, Andrew Lunn wrote:
> On Fri, Mar 29, 2024 at 10:23:20AM +0100, Wojciech Drewek wrote:
>> Some modules use nonstandard power levels. Adjust ethtool
>> module implementation to support new attributes that will allow user
>> to change maximum power.
>>
>> Add three new get attributes:
>> ETHTOOL_A_MODULE_MAX_POWER_SET (used for set as well) - currently set
>>   maximum power in the cage
>> ETHTOOL_A_MODULE_MIN_POWER_ALLOWED - minimum power allowed in the
>>   cage reported by device
>> ETHTOOL_A_MODULE_MAX_POWER_ALLOWED - maximum power allowed in the
>>   cage reported by device
> 
> I'm confused. The cage has two power pins, if you look at the table
> here:
> 
> https://www.embrionix.com/resource/how-to-design-with-video-SFP
> 
> There is VccT and VccR. I would expect there is a power regulator
> supplying these pins. By default, you can draw 1W from that
> regulator. The board however might be designed to support more power,
> so those regulators could supply more power. And the board has also
> been designed to dump the heat if more power is consumed.
> 
> So, ETHTOOL_A_MODULE_MIN_POWER_ALLOWED is about the minimum power that
> regulator can supply? Does that make any sense?
> 
> ETHTOOL_A_MODULE_MAX_POWER_ALLOWED is about the maximum power the
> regulator can supply and the cooling system can dump heat?
> 
> Then what does ETHTOOL_A_MODULE_MAX_POWER_SET mean? power in the cage?
> The cage is passive. It does not consume power. It is the module which
> does. Is this telling the module it can consume up to this amount of
> power?

Right, all of those attributes describe restrictions for modules that
can be plugged into the given cage. ETHTOOL_A_MODULE_MAX_POWER_SET is
currently set maximum. The other two define the range of values that
ETHTOOL_A_MODULE_MAX_POWER_SET can take.

I hope that answers your question.

> 
> 	Andrew
>