Re: [PATCH 1/2] staging: iio: ad7606: replace range/range_available with corresponding scale

From: Jonathan Cameron <jic23@kernel.org>
To: Linus Walleij <linus.walleij@linaro.org>,
	Lars-Peter Clausen <lars@metafoo.de>
Cc: Eva Rachel Retuya <eraretuya@gmail.com>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Michael Hennerich <Michael.Hennerich@analog.com>,
	Hartmut Knaack <knaack.h@gmx.de>,
	Peter Meerwald <pmeerw@pmeerw.net>,
	Greg KH <gregkh@linuxfoundation.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <Mark.Rutland@arm.com>
Subject: Re: [PATCH 1/2] staging: iio: ad7606: replace range/range_available with corresponding scale
Date: Sat, 19 Nov 2016 12:32:42 +0000	[thread overview]
Message-ID: <f381ab09-7bad-acea-ead2-a6a370598918@kernel.org> (raw)
In-Reply-To: <CACRpkdbWqxUWc+40AYSY7XX2ZFYSZEBcU3FusOrunG+-GCZGwQ@mail.gmail.com>

On 14/11/16 23:12, Linus Walleij wrote:
> On Mon, Nov 14, 2016 at 7:53 PM, Lars-Peter Clausen <lars@metafoo.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
> 