Re: [PATCH 1/2] iio: sun4i-lradc: Add binding documentation

[Hans de Goede]

Hi,

On 02-07-16 13:02, Maxime Ripard wrote:
> On Sat, Jul 02, 2016 at 11:32:07AM +0200, Hans de Goede wrote:
> > Hi,
> >
> > On 02-07-16 11:12, Chen-Yu Tsai wrote:
> > > Hi,
> > >
> > > On Sat, Jul 2, 2016 at 5:00 AM, Alexandre Belloni
> > > <alexandre.belloni@xxxxxxxxxxxxxxxxxx> wrote:
> > > > Document the bindings for the Allwinner LRADC.
> > >
> > > We already have Documentation/devicetree/bindings/input/sun4i-lradc-keys.txt
> > > and I'm pretty sure Hans (CC-ed) argued that this is not a generic ADC
> > > block.
> >
> > Right, this block is used on many tablets and some dev boards to
> > provide buttons (as in the hid type) and the block is designed for
> > this purpose, giving an irq when the adc level crosses a certain
> > threshold.
> >
> > Sure it can be used in a more generic way, but that is not its
> > primary goal.
>
> We've always had a different view on this, but it's a detail :)
>
> > So any generic purpose adc driver must not break the current
> > use-case (which is already used in mainline kernel dts files
> > in plenty of cases).
>
> Yep.
>
> > I believe that the best way to deal with this is to add an
> > "allwinner,general-purpose-mode" flag to the existing binding
> > (as well as document general purpose mode in the existing
> > binding rather then in a new binding doc).
> >
> > That seems to be the right thing to do purely looking at this
> > from a dt binding pov.
>
> There's a way simpler solution: if there's no child nodes, it's meant
> to be used as an ADC, otherwise, as input.
>
> The logic will have to be a bit more complex than that, since there's
> two channels, and you could only require one for the buttons, leaving
> the other one available as an ADC.
>
> But that doesn't require any new property.

True, if there are no button nodes, then go general-purpose will
work too.

> > For the implementation of this we can simpy have 2 drivers,
> > then both drivers can check the flag and if present return
> > -ENODEV from the existing input driver and likewise if not
> > present return -ENODEV from the iio driver.
> >
> > We may actually use a similar solution for the touchscreen
> > controller which can also be alternatively used as a generic
> > purpose adc.
>
> There's no need to keep both drivers as long as we keep the features
> and bindings.

That is also true.

Regards,

Hans