Re: Removal of regulator-boot-on/always-on when a consumer exists

From: Fabio Estevam
Date: Mon Sep 26 2016 - 13:26:36 EST

On Mon, Sep 26, 2016 at 1:57 PM, Mark Brown <broonie@xxxxxxxxxx> wrote:

> Like I say I can't give you a definitive answer on this without looking
> at the actual hardware and what it needs. Based on what you're saying
> it sounds like it won't be an issue from the point of view of disrupting
> other users but without knowing the hardware I can't tell if the
> connected device can safely have power removed, sometimes devices don't
> like having only one of many supplies removed.

Ok, let me give you more details: we power the board with an external
5V power supply, then a discrete regulator generates 3.3V to the CAN
transceiver chip.

Software has no influence on this 3.3V rail, which stays powered as
long as the board is powered.

According to Documentation/devicetree/bindings/regulator/regulator.txt:

- regulator-always-on: boolean, regulator should never be disabled
- regulator-boot-on: bootloader/firmware enabled regulator

and the dts looks like:

reg_3p3v: regulator-3p3v {
compatible = "regulator-fixed";
regulator-name = "3P3V";
regulator-min-microvolt = <3300000>;
regulator-max-microvolt = <3300000>;

&can1 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_flexcan1>;
xceiver-supply = <&reg_3p3v>;

The flexcan driver (which is the consumer of reg_3p3v) will call
regulator_disable() when can1 is not used. Calling regulator_disable
on reg_3p3v will not physically remove power from the 3.3V, so should
we use "regulator-always-on" or not in this case?

About "regulator-boot-on": since it was not the bootloader/firmware
that was responsible for enabling such regulator, I think this could
be removed from the dts.

Thanks for the clarification.