Re: [PATCH net-next 0/2] net: sfp: Describe and handle regulators

[Romain Gantois]

Hi Russell,

On Tuesday, 3 March 2026 16:10:12 CET Russell King (Oracle) wrote:
> On Tue, Mar 03, 2026 at 02:54:25PM +0100, Romain Gantois wrote:
> > Hi everyone,
> > 
> > This series describes regulators supplying the VccT and VccR pins of an
> > SFP
> > cage or soldered-down transceiver.
> > 
> > These regulators can then be turned on only when the SFP device is probed,
> > thus saving power on systems which only load SFP cage support at certain
> > times, or load SFP device descriptions via device tree overlays.
> > 
> > Please let me know what you think.
> 
> As ever, I don't want to be adding support for stuff into mainline
> which doesn't ever get used - historically, we've had a lot of that.
> So, any patch set which adds some kind of facility like this needs to
> be accompanied by a user of it.
> 

I understand, though I'm dealing with an out-of-tree board but I understand 
that this doesn't really count as a valid first use case.

> This is especially true in this case, because I want to see why you're
> wanting to have two regulators, when INF-8074 suggests that both VccT
> and VccR should be derived from the same supply. The reason the
> modules have separate supplies for the transmitter and receiver is
> because the host side has the supply filtering networks to ensure
> cross-talk between each is kept to a minimum.

Interesting, I wasn't aware of this. I thought it was something like "being 
able to shut down the transmitter side only while waiting for a WoL packet".

It seems like there won't be a v2 anyway but I just wanted to explain why I 
went with two regulators in the first place.

Thanks,

-- 
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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