linux-kernel - Re: [PATCH] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request

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Message-ID: <CAAVeFuKC19AK8BjM7OBm=FWm0ua5YJXoGRkpOvM1TWkz9yOZ5Q@mail.gmail.com>
Date:	Thu, 17 Jul 2014 16:26:40 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request_one

On Thu, Jul 17, 2014 at 3:37 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> On 07/16/2014 11:09 PM, Alexandre Courbot wrote:
>>
>> On Thu, Jul 17, 2014 at 8:11 AM, Guenter Roeck <linux@...ck-us.net> wrote:
>>>
>>> The gpio include file and the gpio documentation declare and document
>>> GPIOF_ACTIVE_LOW as one of the flags to be passed to gpio_request_one
>>> and related functions. However, the flag is not evaluated or used.
>>>
>>> Check the flag in gpio_request_one and set the gpio internal flag
>>> FLAG_ACTIVE_LOW if it is set.
>>
>>
>> What is the point since the integer GPIO API has no clue of the
>> active-low status of a GPIO? It is only used by the gpiod and sysfs
>> interfaces.
>>
>
> One can use gpio_request_one() to export a gpio pin to user space from
> the kernel. That code path does use the flag, as you point out yourself
> above.

Ok, in that case I suppose it makes sense.

Reviewed-by: Alexandre Courbot <acourbot@...dia.com>

> One could also argue that the integer gpio API _should_ support this as
> well,
> but that is a different question.

Probably not going to happen. The integer GPIO interface is deprecated
and users who need new features should seriously consider switching to
gpiod.
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