[RFC PATCH v2] gpiolib: add gpio get direction callback support

[RFC PATCH v2] gpiolib: add gpio get direction callback support

[Mathias Nyman]

Add .get_direction callback to gpio_chip. This allows gpiolib
to check the current direction of a gpio.
Used to show the correct gpio direction in sysfs and debug entries.

If callback is not set then gpiolib will work as previously;
e.g. guessing everything is input until a direction is set.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 drivers/gpio/gpiolib.c     |   38 +++++++++++++++++++++++++++++++++++++-
 include/asm-generic/gpio.h |    5 ++++-
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index de0213c..141f793 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -191,6 +191,32 @@ err:
 	return ret;
 }
 
+/* caller ensures gpio is valid and requested, chip->get_direction may sleep  */
+static int gpio_get_direction(unsigned gpio)
+{
+	struct gpio_chip	*chip;
+	struct gpio_desc	*desc = &gpio_desc[gpio];
+	int			status = -EINVAL;
+
+	chip = gpio_to_chip(gpio);
+	gpio -= chip->base;
+
+	if (!chip->get_direction)
+		return status;
+
+	status = chip->get_direction(chip, gpio);
+	if (status > 0) {
+		/* GPIOF_DIR_IN, or other positive */
+		status = 1;
+		clear_bit(FLAG_IS_OUT, &desc->flags);
+	}
+	if (status == 0) {
+		/* GPIOF_DIR_OUT */
+		set_bit(FLAG_IS_OUT, &desc->flags);
+	}
+	return status;
+}
+
 #ifdef CONFIG_GPIO_SYSFS
 
 /* lock protects against unexport_gpio() being called while
@@ -223,6 +249,7 @@ static ssize_t gpio_direction_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
 	const struct gpio_desc	*desc = dev_get_drvdata(dev);
+	unsigned		gpio = desc - gpio_desc;
 	ssize_t			status;
 
 	mutex_lock(&sysfs_lock);
@@ -230,6 +257,7 @@ static ssize_t gpio_direction_show(struct device *dev,
 	if (!test_bit(FLAG_EXPORT, &desc->flags))
 		status = -EIO;
 	else
+		gpio_get_direction(gpio);
 		status = sprintf(buf, "%s\n",
 			test_bit(FLAG_IS_OUT, &desc->flags)
 				? "out" : "in");
@@ -1073,6 +1101,7 @@ int gpiochip_add(struct gpio_chip *chip)
 			 * inputs (often with pullups enabled) so power
 			 * usage is minimized.  Linux code should set the
 			 * gpio direction first thing; but until it does,
+			 * and in case chip->get_direction is not set,
 			 * we may expose the wrong direction in sysfs.
 			 */
 			gpio_desc[id].flags = !chip->direction_input
@@ -1224,9 +1253,15 @@ int gpio_request(unsigned gpio, const char *label)
 			desc_set_label(desc, NULL);
 			module_put(chip->owner);
 			clear_bit(FLAG_REQUESTED, &desc->flags);
+			goto done;
 		}
 	}
-
+	if (chip->get_direction) {
+		/* chip->get_direction may sleep */
+		spin_unlock_irqrestore(&gpio_lock, flags);
+		gpio_get_direction(gpio);
+		spin_lock_irqsave(&gpio_lock, flags);
+	}
 done:
 	if (status)
 		pr_debug("gpio_request: gpio-%d (%s) status %d\n",
@@ -1762,6 +1797,7 @@ static void gpiolib_dbg_show(struct seq_file *s, struct gpio_chip *chip)
 		if (!test_bit(FLAG_REQUESTED, &gdesc->flags))
 			continue;
 
+		gpio_get_direction(gpio);
 		is_out = test_bit(FLAG_IS_OUT, &gdesc->flags);
 		seq_printf(s, " gpio-%-3d (%-20.20s) %s %s",
 			gpio, gdesc->label,
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 365ea09..d8e8c26 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -56,6 +56,8 @@ struct device_node;
  *	enabling module power and clock; may sleep
  * @free: optional hook for chip-specific deactivation, such as
  *	disabling module power and clock; may sleep
+ * @get_direction: returns direction for signal "offset", 0=out, 1=in,
+ *	(same as GPIOF_DIR_XXX), or negative error
  * @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
@@ -98,7 +100,8 @@ struct gpio_chip {
 						unsigned offset);
 	void			(*free)(struct gpio_chip *chip,
 						unsigned offset);
-
+	int			(*get_direction)(struct gpio_chip *chip,
+						unsigned offset);
 	int			(*direction_input)(struct gpio_chip *chip,
 						unsigned offset);
 	int			(*get)(struct gpio_chip *chip,
-- 
1.7.4.1

Re: [RFC PATCH v2] gpiolib: add gpio get direction callback support

[Linus Walleij]

On Wed, Oct 24, 2012 at 4:25 PM, Mathias Nyman
<mathias.nyman@linux.intel.com> wrote:

> Add .get_direction callback to gpio_chip. This allows gpiolib
> to check the current direction of a gpio.
> Used to show the correct gpio direction in sysfs and debug entries.
>
> If callback is not set then gpiolib will work as previously;
> e.g. guessing everything is input until a direction is set.
>
> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>

I buy into this concept.

Patch applied.

Unless Grant protests, it stays in.

Thanks for working on this!
Linus Walleij