Date: Sat, 30 Mar 2024 23:14:10 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Wojciech Drewek <wojciech.drewek@...el.com>
Cc: netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
	simon.horman@...igine.com, 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 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?

	Andrew

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Date: Sat, 30 Mar 2024 23:14:10 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Wojciech Drewek <wojciech.drewek@...el.com>
Cc: netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
	simon.horman@...igine.com, 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
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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?

	Andrew

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