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

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Date:	Wed, 16 Jul 2014 23:37:48 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Alexandre Courbot <gnurou@...il.com>
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 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.

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

Guenter

>>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>>   drivers/gpio/gpiolib.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
>> index 2ebc907..43d9e34 100644
>> --- a/drivers/gpio/gpiolib.c
>> +++ b/drivers/gpio/gpiolib.c
>> @@ -1842,6 +1842,9 @@ int gpio_request_one(unsigned gpio, unsigned long flags, const char *label)
>>          if (flags & GPIOF_OPEN_SOURCE)
>>                  set_bit(FLAG_OPEN_SOURCE, &desc->flags);
>>
>> +       if (flags & GPIOF_ACTIVE_LOW)
>> +               set_bit(FLAG_ACTIVE_LOW, &desc->flags);
>> +
>>          if (flags & GPIOF_DIR_IN)
>>                  err = gpiod_direction_input(desc);
>>          else
>> --
>> 1.9.1
>>
>
>

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