linux-kernel - Re: io-domain voltages as regulators?

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Message-ID: <CACRpkdaJS0PUDLaCnrhtiuXPf4ccx51uNTqYWVWm47mhOhGEbA@mail.gmail.com>
Date:	Mon, 11 Aug 2014 09:44:22 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Heiko Stübner <heiko@...ech.de>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Mark Brown <broonie@...nel.org>, Addy Ke <addy.ke@...k-chips.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: io-domain voltages as regulators?

On Mon, Aug 4, 2014 at 12:18 AM, Heiko Stübner <heiko@...ech.de> wrote:

[Adding Ulf Hansson to this discussion...]

> Hi Mark, Linus,
>
> I'd like to clarify what the appropriate way to handle pin output voltages is.
> On the Rockchip SoCs the voltage for some groups of pins can be set between
> 3.3V and 1.8V ... like the MMC/SD pins who need this to support UHS mode
> cards.

This is called "vqmmc" in the mmc/sd subsystem.

grep for mmc_set_signal_voltage() in drivers/mmc/core/*

In drivers/mmc/core/core.c, you find:

 mmc->supply.vqmmc = devm_regulator_get_optional(dev, "vqmmc");

Which gets the regulator to set the signal voltage, if such
a regulator is specified for the host.

Very simple and straight-forward, and handled by the MMC core.

> In [0] when talking about something different, Linus Walleij described a
> similar case as
>
> "I think we need to have a discussion with Mark Brown on how to
> handle this.
> We have previously had the case of MMC/SD level-shifters, where
> a certain setting gives a certain level of signals out, and another setting
> gives another level. Like two discrete levels.
> So we modeled that as a regulator provider inside the pin control
> driver eventually, see sh-pfc/pfc-sh73a0.c"
>
> As this sound like exactly the thing I'm trying to solve, is handling this via
> a regulator the correct general way?

Ithinkso.

Yours,
Linus Walleij
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