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Commit 35e8bb51 authored by David Brownell's avatar David Brownell Committed by Linus Torvalds
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gpiolib: request/free hooks 



Add a new internal mechanism to gpiolib to support low power
operations by letting gpio_chip instances see when their GPIOs
are in use.  When no GPIOs are active, chips may be able to
enter lower powered runtime states by disabling clocks and/or
power domains.

Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Cc: "Magnus Damm" <magnus.damm@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 93a22f8b

Documentation/gpio.txt

+4 −0
Original line number Diff line number Diff line
@@ -240,6 +240,10 @@ signal, or (b) something wrongly believes it's safe to remove drivers 
needed to manage a signal that's in active use.  That is, requesting a

GPIO can serve as a kind of lock.



Some platforms may also use knowledge about what GPIOs are active for

power management, such as by powering down unused chip sectors and, more

easily, gating off unused clocks.



These two calls are optional because not not all current Linux platforms

offer such functionality in their GPIO support; a valid implementation

could return success for all gpio_request() calls.  Unlike the other calls,

drivers/gpio/gpiolib.c

+78 −13
Original line number Diff line number Diff line
@@ -67,17 +67,28 @@ static inline void desc_set_label(struct gpio_desc *d, const char *label) 
 * when setting direction, and otherwise illegal.  Until board setup code

 * and drivers use explicit requests everywhere (which won't happen when

 * those calls have no teeth) we can't avoid autorequesting.  This nag

 * message should motivate switching to explicit requests...

 * message should motivate switching to explicit requests... so should

 * the weaker cleanup after faults, compared to gpio_request().

 */

static void gpio_ensure_requested(struct gpio_desc *desc)

static int gpio_ensure_requested(struct gpio_desc *desc, unsigned offset)

{

	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {

		pr_warning("GPIO-%d autorequested\n", (int)(desc - gpio_desc));

		struct gpio_chip *chip = desc->chip;

		int gpio = chip->base + offset;



		if (!try_module_get(chip->owner)) {

			pr_err("GPIO-%d: module can't be gotten \n", gpio);

			clear_bit(FLAG_REQUESTED, &desc->flags);

			/* lose */

			return -EIO;

		}

		pr_warning("GPIO-%d autorequested\n", gpio);

		desc_set_label(desc, "[auto]");

		if (!try_module_get(desc->chip->owner))

			pr_err("GPIO-%d: module can't be gotten \n",

					(int)(desc - gpio_desc));

		/* caller must chip->request() w/o spinlock */

		if (chip->request)

			return 1;

	}

	return 0;

}



/* caller holds gpio_lock *OR* gpio is marked as requested */
@@ -752,6 +763,7 @@ EXPORT_SYMBOL_GPL(gpiochip_remove); 
int gpio_request(unsigned gpio, const char *label)

{

	struct gpio_desc	*desc;

	struct gpio_chip	*chip;

	int			status = -EINVAL;

	unsigned long		flags;
@@ -760,14 +772,15 @@ int gpio_request(unsigned gpio, const char *label) 
	if (!gpio_is_valid(gpio))

		goto done;

	desc = &gpio_desc[gpio];

	if (desc->chip == NULL)

	chip = desc->chip;

	if (chip == NULL)

		goto done;



	if (!try_module_get(desc->chip->owner))

	if (!try_module_get(chip->owner))

		goto done;



	/* NOTE:  gpio_request() can be called in early boot,

	 * before IRQs are enabled.

	 * before IRQs are enabled, for non-sleeping (SOC) GPIOs.

	 */



	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
@@ -775,7 +788,20 @@ int gpio_request(unsigned gpio, const char *label) 
		status = 0;

	} else {

		status = -EBUSY;

		module_put(desc->chip->owner);

		module_put(chip->owner);

	}



	if (chip->request) {

		/* chip->request may sleep */

		spin_unlock_irqrestore(&gpio_lock, flags);

		status = chip->request(chip, gpio - chip->base);

		spin_lock_irqsave(&gpio_lock, flags);



		if (status < 0) {

			desc_set_label(desc, NULL);

			module_put(chip->owner);

			clear_bit(FLAG_REQUESTED, &desc->flags);

		}

	}



done:
@@ -791,6 +817,7 @@ void gpio_free(unsigned gpio) 
{

	unsigned long		flags;

	struct gpio_desc	*desc;

	struct gpio_chip	*chip;



	might_sleep();
@@ -804,9 +831,17 @@ void gpio_free(unsigned gpio) 
	spin_lock_irqsave(&gpio_lock, flags);



	desc = &gpio_desc[gpio];

	if (desc->chip && test_and_clear_bit(FLAG_REQUESTED, &desc->flags)) {

	chip = desc->chip;

	if (chip && test_bit(FLAG_REQUESTED, &desc->flags)) {

		if (chip->free) {

			spin_unlock_irqrestore(&gpio_lock, flags);

			might_sleep_if(extra_checks && chip->can_sleep);

			chip->free(chip, gpio - chip->base);

			spin_lock_irqsave(&gpio_lock, flags);

		}

		desc_set_label(desc, NULL);

		module_put(desc->chip->owner);

		clear_bit(FLAG_REQUESTED, &desc->flags);

	} else

		WARN_ON(extra_checks);
@@ -871,7 +906,9 @@ int gpio_direction_input(unsigned gpio) 
	gpio -= chip->base;

	if (gpio >= chip->ngpio)

		goto fail;

	gpio_ensure_requested(desc);

	status = gpio_ensure_requested(desc, gpio);

	if (status < 0)

		goto fail;



	/* now we know the gpio is valid and chip won't vanish */
@@ -879,9 +916,22 @@ int gpio_direction_input(unsigned gpio) 


	might_sleep_if(extra_checks && chip->can_sleep);



	if (status) {

		status = chip->request(chip, gpio);

		if (status < 0) {

			pr_debug("GPIO-%d: chip request fail, %d\n",

				chip->base + gpio, status);

			/* and it's not available to anyone else ...

			 * gpio_request() is the fully clean solution.

			 */

			goto lose;

		}

	}



	status = chip->direction_input(chip, gpio);

	if (status == 0)

		clear_bit(FLAG_IS_OUT, &desc->flags);

lose:

	return status;

fail:

	spin_unlock_irqrestore(&gpio_lock, flags);
@@ -909,7 +959,9 @@ int gpio_direction_output(unsigned gpio, int value) 
	gpio -= chip->base;

	if (gpio >= chip->ngpio)

		goto fail;

	gpio_ensure_requested(desc);

	status = gpio_ensure_requested(desc, gpio);

	if (status < 0)

		goto fail;



	/* now we know the gpio is valid and chip won't vanish */
@@ -917,9 +969,22 @@ int gpio_direction_output(unsigned gpio, int value) 


	might_sleep_if(extra_checks && chip->can_sleep);



	if (status) {

		status = chip->request(chip, gpio);

		if (status < 0) {

			pr_debug("GPIO-%d: chip request fail, %d\n",

				chip->base + gpio, status);

			/* and it's not available to anyone else ...

			 * gpio_request() is the fully clean solution.

			 */

			goto lose;

		}

	}



	status = chip->direction_output(chip, gpio, value);

	if (status == 0)

		set_bit(FLAG_IS_OUT, &desc->flags);

lose:

	return status;

fail:

	spin_unlock_irqrestore(&gpio_lock, flags);

include/asm-generic/gpio.h

+9 −0
Original line number Diff line number Diff line
@@ -35,6 +35,10 @@ struct module; 
 * @label: for diagnostics

 * @dev: optional device providing the GPIOs

 * @owner: helps prevent removal of modules exporting active GPIOs

 * @request: optional hook for chip-specific activation, such as

 *	enabling module power and clock; may sleep

 * @free: optional hook for chip-specific deactivation, such as

 *	disabling module power and clock; may sleep

 * @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
@@ -67,6 +71,11 @@ struct gpio_chip { 
	struct device		*dev;

	struct module		*owner;



	int			(*request)(struct gpio_chip *chip,

						unsigned offset);

	void			(*free)(struct gpio_chip *chip,

						unsigned offset);



	int			(*direction_input)(struct gpio_chip *chip,

						unsigned offset);

	int			(*get)(struct gpio_chip *chip,