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

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Date:   Sat, 19 Nov 2016 12:32:42 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Lars-Peter Clausen <lars@...afoo.de>
Cc:     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>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>
Subject: Re: [PATCH 1/2] staging: iio: ad7606: replace range/range_available
 with corresponding scale

On 14/11/16 23:12, Linus Walleij wrote:
> 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.
That's a reasonable approach, but I'd certainly like to see a generic binding
to describe it.  It's a pretty common situation.

Seems more likely we'll get a device tree maintainer response if we cc them ;)

So Mark, Rob and thoughts on this?

Thanks,

Jonathan
> 
> Yours,
> Linus Walleij
>