linux-kernel - Re: [PATCH 1/2] staging: iio: ad7606: replace range/range

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Date:   Tue, 15 Nov 2016 00:12:55 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Eva Rachel Retuya <eraretuya@...il.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald <pmeerw@...erw.net>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/2] staging: iio: ad7606: replace range/range_available
 with corresponding scale

On Mon, Nov 14, 2016 at 7:53 PM, Lars-Peter Clausen <lars@...afoo.de> wrote:

> It's about figuring out the setting of a "GPIO" that can't be changed from
> software.
>
> Devices sometimes, instead of a configuration bus like I2C or SPI, use
> simple input pins, that can either be set to high or low, to allow software
> the state of the device. The GPIO API is typically used to configure these pins.
>
> This works fine as long as the pin is connected to a GPIO. But sometimes the
> system designer decides that a settings does not need to be configurable, in
> this case the pin will be tied to logic low or high directly on the PCB
> without any GPIO controller being involved.
>
> Sometimes a driver wants to know how the pin is wired up so it can report to
> userspace this part runs in the following mode and the mode can't be
> changed. In a sense it is like a reverse GPIO hog.
>
> Considering that this is a common usecase the question was how this can be
> implemented in a driver independent way to avoid code duplication and
> slightly different variations of what is effectively the same DT/ACPI binding.
>
> E.g. lets say for a configurable pin you use
>
>         range-gpio = <&gpio ...>;
>
> and for a static pin
>
>         range-gpio-fixed = <1>;
>
> Or something similar.

Aha I understand.

Usually I feel we need not shoehorn stuff into GPIO because it is convenient,
it might be best to leave the GPIO optional and if it is not there, look for
a custom attribute that represents the "hogging" to 0/1. I think trying
to extend GPIO bindings to cover it is overgeneralization, instead go
for a local binding for this kind of devices.

But mainly it is a question to the DT bindings maintainers.

Yours,
Linus Walleij