path: root/drivers/gpio/gpiolib.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/irq.h>
#include <linux/spinlock.h>

#include <asm/gpio.h>


/* Optional implementation infrastructure for GPIO interfaces.
 *
 * Platforms may want to use this if they tend to use very many GPIOs
 * that aren't part of a System-On-Chip core; or across I2C/SPI/etc.
 *
 * When kernel footprint or instruction count is an issue, simpler
 * implementations may be preferred.  The GPIO programming interface
 * allows for inlining speed-critical get/set operations for common
 * cases, so that access to SOC-integrated GPIOs can sometimes cost
 * only an instruction or two per bit.
 */


/* When debugging, extend minimal trust to callers and platform code.
 * Also emit diagnostic messages that may help initial bringup, when
 * board setup or driver bugs are most common.
 *
 * Otherwise, minimize overhead in what may be bitbanging codepaths.
 */
#ifdef	DEBUG
#define	extra_checks	1
#else
#define	extra_checks	0
#endif

/* gpio_lock prevents conflicts during gpio_desc[] table updates.
 * While any GPIO is requested, its gpio_chip is not removable;
 * each GPIO's "requested" flag serves as a lock and refcount.
 */
static DEFINE_SPINLOCK(gpio_lock);

struct gpio_desc {
	struct gpio_chip	*chip;
	unsigned long		flags;
/* flag symbols are bit numbers */
#define FLAG_REQUESTED	0
#define FLAG_IS_OUT	1
#define FLAG_RESERVED	2

#ifdef CONFIG_DEBUG_FS
	const char		*label;
#endif
};
static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];

static inline void desc_set_label(struct gpio_desc *d, const char *label)
{
#ifdef CONFIG_DEBUG_FS
	d->label = label;
#endif
}

/* Warn when drivers omit gpio_request() calls -- legal but ill-advised
 * 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...
 */
static void gpio_ensure_requested(struct gpio_desc *desc)
{
	if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
		pr_warning("GPIO-%d autorequested\n", (int)(desc - gpio_desc));
		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 holds gpio_lock *OR* gpio is marked as requested */
static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
{
	return gpio_desc[gpio].chip;
}

/* dynamic allocation of GPIOs, e.g. on a hotplugged device */
static int gpiochip_find_base(int ngpio)
{
	int i;
	int spare = 0;
	int base = -ENOSPC;

	for (i = ARCH_NR_GPIOS - 1; i >= 0 ; i--) {
		struct gpio_desc *desc = &gpio_desc[i];
		struct gpio_chip *chip = desc->chip;

		if (!chip && !test_bit(FLAG_RESERVED, &desc->flags)) {
			spare++;
			if (spare == ngpio) {
				base = i;
				break;
			}
		} else {
			spare = 0;
			if (chip)
				i -= chip->ngpio - 1;
		}
	}

	if (gpio_is_valid(base))
		pr_debug("%s: found new base at %d\n", __func__, base);
	return base;
}

/**
 * gpiochip_reserve() - reserve range of gpios to use with platform code only
 * @start: starting gpio number
 * @ngpio: number of gpios to reserve
 * Context: platform init, potentially before irqs or kmalloc will work
 *
 * Returns a negative errno if any gpio within the range is already reserved
 * or registered, else returns zero as a success code.  Use this function
 * to mark a range of gpios as unavailable for dynamic gpio number allocation,
 * for example because its driver support is not yet loaded.
 */
int __init gpiochip_reserve(int start, int ngpio)
{
	int ret = 0;
	unsigned long flags;
	int i;

	if (!gpio_is_valid(start) || !gpio_is_valid(start + ngpio))
		return -EINVAL;

	spin_lock_irqsave(&gpio_lock, flags);

	for (i = start; i < start + ngpio; i++) {
		struct gpio_desc *desc = &gpio_desc[i];

		if (desc->chip || test_bit(FLAG_RESERVED, &desc->flags)) {
			ret = -EBUSY;
			goto err;
		}

		set_bit(FLAG_RESERVED, &desc->flags);
	}

	pr_debug("%s: reserved gpios from %d to %d\n",
		 __func__, start, start + ngpio - 1);
err:
	spin_unlock_irqrestore(&gpio_lock, flags);

	return ret;
}

/**
 * gpiochip_add() - register a gpio_chip
 * @chip: the chip to register, with chip->base initialized
 * Context: potentially before irqs or kmalloc will work
 *
 * Returns a negative errno if the chip can't be registered, such as
 * because the chip->base is invalid or already associated with a
 * different chip.  Otherwise it returns zero as a success code.
 *
 * If chip->base is negative, this requests dynamic assignment of
 * a range of valid GPIOs.
 */
int gpiochip_add(struct gpio_chip *chip)
{
	unsigned long	flags;
	int		status = 0;
	unsigned	id;
	int		base = chip->base;

	if ((!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio))
			&& base >= 0) {
		status = -EINVAL;
		goto fail;
	}

	spin_lock_irqsave(&gpio_lock, flags);

	if (base < 0) {
		base = gpiochip_find_base(chip->ngpio);
		if (base < 0) {
			status = base;
			goto fail_unlock;
		}
		chip->base = base;
	}

	/* these GPIO numbers must not be managed by another gpio_chip */
	for (id = base; id < base + chip->ngpio; id++) {
		if (gpio_desc[id].chip != NULL) {
			status = -EBUSY;
			break;
		}
	}
	if (status == 0) {
		for (id = base; id < base + chip->ngpio; id++) {
			gpio_desc[id].chip = chip;
			gpio_desc[id].flags = 0;
		}
	}

fail_unlock:
	spin_unlock_irqrestore(&gpio_lock, flags);
fail:
	/* failures here can mean systems won't boot... */
	if (status)
		pr_err("gpiochip_add: gpios %d..%d (%s) not registered\n",
			chip->base, chip->base + chip->ngpio,
			chip->label ? : "generic");
	return status;
}
EXPORT_SYMBOL_GPL(gpiochip_add);

/**
 * gpiochip_remove() - unregister a gpio_chip
 * @chip: the chip to unregister
 *
 * A gpio_chip with any GPIOs still requested may not be removed.
 */
int gpiochip_remove(struct gpio_chip *chip)
{
	unsigned long	flags;
	int		status = 0;
	unsigned	id;

	spin_lock_irqsave(&gpio_lock, flags);

	for (id = chip->base; id < chip->base + chip->ngpio; id++) {
		if (test_bit(FLAG_REQUESTED, &gpio_desc[id].flags)) {
			status = -EBUSY;
			break;
		}
	}
	if (status == 0) {
		for (id = chip->base; id < chip->base + chip->ngpio; id++)
			gpio_desc[id].chip = NULL;
	}