[PATCH] arm64: dts: allwinner: a64: bananapi-m64: Add LED device node

[maxime.ripard@free-electrons.com (Maxime Ripard)]

On Tue, Dec 05, 2017 at 09:00:37PM +0800, Chen-Yu Tsai wrote:
> On Tue, Dec 5, 2017 at 6:05 PM, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > Hi,
> >
> > On Sat, Dec 02, 2017 at 12:27:33AM +0800, Chen-Yu Tsai wrote:
> >> The Bananapi-M64 has 3 LEDS in red, green, and blue. These are toggled
> >> via GPIO lines, which drive transistors that control current across the
> >> LEDS. The red LED is by default on, via an additional pull-up on the
> >> control line. We consider this means that it is a power indicator.
> >> So we set the "default-on" property for it.
> >>
> >> The pingroups the GPIO lines belong to require external regulators be
> >> enabled to be able to drive the GPIO high. These regulators also have
> >> other purposes. However the pin controller does not have bindings for
> >> regulators. Here we just set them to always-on.
> >
> > I guess we should take the opportunity to do just that.
> >
> > We have been deferring this for quite some time now, this is a perfect
> > occasion to do it once and for all :)
> 
> True. But right now I don't see an elegant solution. What is the purpose
> of having the regulator tied to pinctrl / GPIO? You can't have the pinctrl
> driver asking for the regulator at probe time, as it might not be available
> or even have a cyclic dependency (because the PMIC is I2C driven, which
> needs an I2C controller, which needs the pinctrl).

Ah, right, you definitely have a circular dependency.

> If you defer fetching the regulator to a later point, you might end
> up with an inconsistent state.  Again with the I2C driven regulator
> example, what happens if the regulator core decides to turn the
> regulator off before the pinctrl side has a chance to take a
> reference and enable it?

I guess you could implement something based on the an asynchronous
regulator_get. You call regulator_get_async (or whatever) in the
pinctrl probe, and get notified as soon as it is registered so that
you can act upon it.

Anyway, this is a bit too much to ask to enable 3 LEDs... I've applied
that patch.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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