[PATCH RESEND] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request_one functions

[PATCH RESEND] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request_one functions

[Guenter Roeck]

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.

This can cause problems in at least two areas: First, the same API can
be used to auto-export pins to user space. The missing support for
GPIOF_ACTIVE_LOW results in unexpected behavior for such auto-exported
pins. Second, the requested gpio pin can be convered for use by
gpiod functions with gpio_to_desc(). While gpio API functions do not
support GPIOF_ACTIVE_LOW, gpiod functions do, which again results in
unexpected behavior.

Check the flag in gpio_request_one and set the gpio internal flag
FLAG_ACTIVE_LOW if it is set to address those problems.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
---
Resent with added rationale.

 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

Re: [PATCH RESEND] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request_one functions

[Linus Walleij]

On Mon, Jul 21, 2014 at 8:12 PM, Guenter Roeck <linux@roeck-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.
>
> This can cause problems in at least two areas: First, the same API can
> be used to auto-export pins to user space. The missing support for
> GPIOF_ACTIVE_LOW results in unexpected behavior for such auto-exported
> pins. Second, the requested gpio pin can be convered for use by
> gpiod functions with gpio_to_desc(). While gpio API functions do not
> support GPIOF_ACTIVE_LOW, gpiod functions do, which again results in
> unexpected behavior.
>
> Check the flag in gpio_request_one and set the gpio internal flag
> FLAG_ACTIVE_LOW if it is set to address those problems.
>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

Patch applied after manually rebasing so it hits gpiolib-legacy.c.

Yours,
Linus Walleij