linux-kernel - [PATCH v4 2/4] gpiolib: Add ability to get GPIO direction

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Date:	Fri, 25 Feb 2011 15:26:19 -0600
From:	Peter Tyser <ptyser@...-inc.com>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Tyser <ptyser@...-inc.com>, Alek Du <alek.du@...el.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Eric Miao <eric.y.miao@...il.com>,
	Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Joe Perches <joe@...ches.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: [PATCH v4 2/4] gpiolib: Add ability to get GPIO direction

Add a new get_direction() function to the gpio_chip structure.  This is
useful so that the direction of a GPIO can be determined when its
initially exported.  Previously, the direction defaulted to "unknown"
regardless of the actual configuration of the GPIO.

If a GPIO driver implements get_direction(), it is called in
gpio_request() to set the initial direction of the GPIO accurately.

Cc: Alek Du <alek.du@...el.com>
Cc: Samuel Ortiz <sameo@...ux.intel.com>
Cc: David Brownell <dbrownell@...rs.sourceforge.net>
Cc: Eric Miao <eric.y.miao@...il.com>
Cc: Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>
Cc: Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc: Joe Perches <joe@...ches.com>
Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
Cc: Grant Likely <grant.likely@...retlab.ca>
Signed-off-by: Peter Tyser <ptyser@...-inc.com>
---
Changes since v1:
- Add support for "unknown" direction

Changes since v2:
  Based on Wolfram's feedback:
- Use GPIOF_DIR_* flags as returns from get_direction()
- Call spin_lock_irqsave() to before setting flags

Changes since v3:
- Removed "pin" references from the commit message
- Added might_sleep() call
- Made the direction always be set in gpio_request()

 drivers/gpio/gpiolib.c     |   25 +++++++++++++++++++++++++
 include/asm-generic/gpio.h |    4 ++++
 2 files changed, 29 insertions(+), 0 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index eb74311..106164f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1174,6 +1174,7 @@ int gpio_request(unsigned gpio, const char *label)
 	struct gpio_desc	*desc;
 	struct gpio_chip	*chip;
 	int			status = -EINVAL;
+	int			dir = -1; /* Default to unknown direction */
 	unsigned long		flags;
 
 	spin_lock_irqsave(&gpio_lock, flags);
@@ -1214,6 +1215,30 @@ int gpio_request(unsigned gpio, const char *label)
 		}
 	}
 
+	if (chip->get_direction) {
+		/* chip->get_direction may sleep */
+		spin_unlock_irqrestore(&gpio_lock, flags);
+		might_sleep_if(chip->can_sleep);
+		dir = chip->get_direction(chip, gpio - chip->base);
+		spin_lock_irqsave(&gpio_lock, flags);
+	}
+
+	switch (dir) {
+	case GPIOF_DIR_OUT:
+		set_bit(FLAG_DIR_OUT, &desc->flags);
+		clear_bit(FLAG_DIR_IN, &desc->flags);
+		break;
+	case GPIOF_DIR_IN:
+		set_bit(FLAG_DIR_IN, &desc->flags);
+		clear_bit(FLAG_DIR_OUT, &desc->flags);
+		break;
+	default:
+		/* Direction isn't known */
+		clear_bit(FLAG_DIR_OUT, &desc->flags);
+		clear_bit(FLAG_DIR_IN, &desc->flags);
+		break;
+	}
+
 done:
 	if (status)
 		pr_debug("gpio_request: gpio-%d (%s) status %d\n",
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index ff5c660..6af5a3e 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -57,6 +57,8 @@ struct device_node;
  * @direction_input: configures signal "offset" as input, or returns error
  * @get: returns value for signal "offset"; for output signals this
  *	returns either the value actually sensed, or zero
+ * @get_direction: optional hook to determine if a GPIO signal is configured
+ *	as an input, output, or unknown
  * @direction_output: configures signal "offset" as output, or returns error
  * @set: assigns output value for signal "offset"
  * @to_irq: optional hook supporting non-static gpio_to_irq() mappings;
@@ -101,6 +103,8 @@ struct gpio_chip {
 						unsigned offset);
 	int			(*get)(struct gpio_chip *chip,
 						unsigned offset);
+	int			(*get_direction)(struct gpio_chip *chip,
+						unsigned offset);
 	int			(*direction_output)(struct gpio_chip *chip,
 						unsigned offset, int value);
 	int			(*set_debounce)(struct gpio_chip *chip,
-- 
1.7.0.4

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