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

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Date:	Mon, 21 Jul 2014 11:12:16 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	linux-gpio@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH RESEND] gpio: Add support for GPIOF_ACTIVE_LOW to gpio_request_one functions

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@...ck-us.net>
Reviewed-by: Alexandre Courbot <acourbot@...dia.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

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