gpiolib.c 73.9 KB
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#include <linux/kernel.h>
#include <linux/module.h>
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#include <linux/interrupt.h>
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#include <linux/irq.h>
#include <linux/spinlock.h>
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#include <linux/list.h>
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#include <linux/device.h>
#include <linux/err.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>
#include <linux/gpio.h>
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#include <linux/of_gpio.h>
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#include <linux/idr.h>
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#include <linux/slab.h>
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#include <linux/acpi.h>
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#include <linux/gpio/driver.h>
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#include "gpiolib.h"

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#define CREATE_TRACE_POINTS
#include <trace/events/gpio.h>
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/* Implementation infrastructure for GPIO interfaces.
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 *
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 * 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.
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 */


/* 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
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#define FLAG_EXPORT	2	/* protected by sysfs_lock */
#define FLAG_SYSFS	3	/* exported via /sys/class/gpio/control */
#define FLAG_TRIG_FALL	4	/* trigger on falling edge */
#define FLAG_TRIG_RISE	5	/* trigger on rising edge */
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#define FLAG_ACTIVE_LOW	6	/* value has active low */
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#define FLAG_OPEN_DRAIN	7	/* Gpio is open drain type */
#define FLAG_OPEN_SOURCE 8	/* Gpio is open source type */
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#define FLAG_USED_AS_IRQ 9	/* GPIO is connected to an IRQ */
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#define ID_SHIFT	16	/* add new flags before this one */
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#define GPIO_FLAGS_MASK		((1 << ID_SHIFT) - 1)
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#define GPIO_TRIGGER_MASK	(BIT(FLAG_TRIG_FALL) | BIT(FLAG_TRIG_RISE))
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#ifdef CONFIG_DEBUG_FS
	const char		*label;
#endif
};
static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];

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#define GPIO_OFFSET_VALID(chip, offset) (offset >= 0 && offset < chip->ngpio)

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static DEFINE_MUTEX(gpio_lookup_lock);
static LIST_HEAD(gpio_lookup_list);
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static LIST_HEAD(gpio_chips);

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#ifdef CONFIG_GPIO_SYSFS
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static DEFINE_IDR(dirent_idr);
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#endif

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static int gpiod_request(struct gpio_desc *desc, const char *label);
static void gpiod_free(struct gpio_desc *desc);

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/* With descriptor prefix */

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#ifdef CONFIG_DEBUG_FS
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#define gpiod_emerg(desc, fmt, ...)					       \
	pr_emerg("gpio-%d (%s): " fmt, desc_to_gpio(desc), desc->label ? : "?",\
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                 ##__VA_ARGS__)
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#define gpiod_crit(desc, fmt, ...)					       \
	pr_crit("gpio-%d (%s): " fmt, desc_to_gpio(desc), desc->label ? : "?", \
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                 ##__VA_ARGS__)
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#define gpiod_err(desc, fmt, ...)					       \
	pr_err("gpio-%d (%s): " fmt, desc_to_gpio(desc), desc->label ? : "?",  \
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                 ##__VA_ARGS__)
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#define gpiod_warn(desc, fmt, ...)					       \
	pr_warn("gpio-%d (%s): " fmt, desc_to_gpio(desc), desc->label ? : "?", \
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                 ##__VA_ARGS__)
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#define gpiod_info(desc, fmt, ...)					       \
	pr_info("gpio-%d (%s): " fmt, desc_to_gpio(desc), desc->label ? : "?", \
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                ##__VA_ARGS__)
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#define gpiod_dbg(desc, fmt, ...)					       \
	pr_debug("gpio-%d (%s): " fmt, desc_to_gpio(desc), desc->label ? : "?",\
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                 ##__VA_ARGS__)
#else
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#define gpiod_emerg(desc, fmt, ...)					\
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	pr_emerg("gpio-%d: " fmt, desc_to_gpio(desc), ##__VA_ARGS__)
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#define gpiod_crit(desc, fmt, ...)					\
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	pr_crit("gpio-%d: " fmt, desc_to_gpio(desc), ##__VA_ARGS__)
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#define gpiod_err(desc, fmt, ...)					\
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	pr_err("gpio-%d: " fmt, desc_to_gpio(desc), ##__VA_ARGS__)
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#define gpiod_warn(desc, fmt, ...)					\
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	pr_warn("gpio-%d: " fmt, desc_to_gpio(desc), ##__VA_ARGS__)
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#define gpiod_info(desc, fmt, ...)					\
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	pr_info("gpio-%d: " fmt, desc_to_gpio(desc), ##__VA_ARGS__)
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#define gpiod_dbg(desc, fmt, ...)					\
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	pr_debug("gpio-%d: " fmt, desc_to_gpio(desc), ##__VA_ARGS__)
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#endif
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/* With chip prefix */

#define chip_emerg(chip, fmt, ...)					\
	pr_emerg("GPIO chip %s: " fmt, chip->label, ##__VA_ARGS__)
#define chip_crit(chip, fmt, ...)					\
	pr_crit("GPIO chip %s: " fmt, chip->label, ##__VA_ARGS__)
#define chip_err(chip, fmt, ...)					\
	pr_err("GPIO chip %s: " fmt, chip->label, ##__VA_ARGS__)
#define chip_warn(chip, fmt, ...)					\
	pr_warn("GPIO chip %s: " fmt, chip->label, ##__VA_ARGS__)
#define chip_info(chip, fmt, ...)					\
	pr_info("GPIO chip %s: " fmt, chip->label, ##__VA_ARGS__)
#define chip_dbg(chip, fmt, ...)					\
	pr_debug("GPIO chip %s: " fmt, chip->label, ##__VA_ARGS__)

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

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/*
 * Return the GPIO number of the passed descriptor relative to its chip
 */
static int gpio_chip_hwgpio(const struct gpio_desc *desc)
{
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	return desc - &desc->chip->desc[0];
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}

/**
 * Convert a GPIO number to its descriptor
 */
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struct gpio_desc *gpio_to_desc(unsigned gpio)
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{
	if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio))
		return NULL;
	else
		return &gpio_desc[gpio];
}
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EXPORT_SYMBOL_GPL(gpio_to_desc);
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/**
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 * Get the GPIO descriptor corresponding to the given hw number for this chip.
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 */
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struct gpio_desc *gpiochip_get_desc(struct gpio_chip *chip,
				    u16 hwnum)
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{
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	if (hwnum >= chip->ngpio)
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		return ERR_PTR(-EINVAL);
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	return &chip->desc[hwnum];
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}
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EXPORT_SYMBOL_GPL(gpiochip_get_desc);
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/**
 * Convert a GPIO descriptor to the integer namespace.
 * This should disappear in the future but is needed since we still
 * use GPIO numbers for error messages and sysfs nodes
 */
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int desc_to_gpio(const struct gpio_desc *desc)
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{
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	return desc - &gpio_desc[0];
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}
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EXPORT_SYMBOL_GPL(desc_to_gpio);
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/* 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
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 * message should motivate switching to explicit requests... so should
 * the weaker cleanup after faults, compared to gpio_request().
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 *
 * NOTE: the autorequest mechanism is going away; at this point it's
 * only "legal" in the sense that (old) code using it won't break yet,
 * but instead only triggers a WARN() stack dump.
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 */
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static int gpio_ensure_requested(struct gpio_desc *desc)
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{
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	const struct gpio_chip *chip = desc->chip;
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	const int gpio = desc_to_gpio(desc);
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	if (WARN(test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0,
			"autorequest GPIO-%d\n", gpio)) {
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		if (!try_module_get(chip->owner)) {
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			gpiod_err(desc, "%s: module can't be gotten\n",
					__func__);
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			clear_bit(FLAG_REQUESTED, &desc->flags);
			/* lose */
			return -EIO;
		}
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		desc_set_label(desc, "[auto]");
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		/* caller must chip->request() w/o spinlock */
		if (chip->request)
			return 1;
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	}
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	return 0;
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}

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/**
 * gpiod_to_chip - Return the GPIO chip to which a GPIO descriptor belongs
 * @desc:	descriptor to return the chip of
 */
struct gpio_chip *gpiod_to_chip(const struct gpio_desc *desc)
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{
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	return desc ? desc->chip : NULL;
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}
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EXPORT_SYMBOL_GPL(gpiod_to_chip);
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/* dynamic allocation of GPIOs, e.g. on a hotplugged device */
static int gpiochip_find_base(int ngpio)
{
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	struct gpio_chip *chip;
	int base = ARCH_NR_GPIOS - ngpio;
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	list_for_each_entry_reverse(chip, &gpio_chips, list) {
		/* found a free space? */
		if (chip->base + chip->ngpio <= base)
			break;
		else
			/* nope, check the space right before the chip */
			base = chip->base - ngpio;
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	}

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	if (gpio_is_valid(base)) {
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		pr_debug("%s: found new base at %d\n", __func__, base);
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		return base;
	} else {
		pr_err("%s: cannot find free range\n", __func__);
		return -ENOSPC;
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	}
}

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/**
 * gpiod_get_direction - return the current direction of a GPIO
 * @desc:	GPIO to get the direction of
 *
 * Return GPIOF_DIR_IN or GPIOF_DIR_OUT, or an error code in case of error.
 *
 * This function may sleep if gpiod_cansleep() is true.
 */
int gpiod_get_direction(const struct gpio_desc *desc)
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{
	struct gpio_chip	*chip;
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	unsigned		offset;
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	int			status = -EINVAL;

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	chip = gpiod_to_chip(desc);
	offset = gpio_chip_hwgpio(desc);
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	if (!chip->get_direction)
		return status;

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	status = chip->get_direction(chip, offset);
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	if (status > 0) {
		/* GPIOF_DIR_IN, or other positive */
		status = 1;
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		/* FLAG_IS_OUT is just a cache of the result of get_direction(),
		 * so it does not affect constness per se */
		clear_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
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	}
	if (status == 0) {
		/* GPIOF_DIR_OUT */
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		set_bit(FLAG_IS_OUT, &((struct gpio_desc *)desc)->flags);
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	}
	return status;
}
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EXPORT_SYMBOL_GPL(gpiod_get_direction);
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#ifdef CONFIG_GPIO_SYSFS

/* lock protects against unexport_gpio() being called while
 * sysfs files are active.
 */
static DEFINE_MUTEX(sysfs_lock);

/*
 * /sys/class/gpio/gpioN... only for GPIOs that are exported
 *   /direction
 *      * MAY BE OMITTED if kernel won't allow direction changes
 *      * is read/write as "in" or "out"
 *      * may also be written as "high" or "low", initializing
 *        output value as specified ("out" implies "low")
 *   /value
 *      * always readable, subject to hardware behavior
 *      * may be writable, as zero/nonzero
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 *   /edge
 *      * configures behavior of poll(2) on /value
 *      * available only if pin can generate IRQs on input
 *      * is read/write as "none", "falling", "rising", or "both"
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 *   /active_low
 *      * configures polarity of /value
 *      * is read/write as zero/nonzero
 *      * also affects existing and subsequent "falling" and "rising"
 *        /edge configuration
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 */

static ssize_t gpio_direction_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
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	const struct gpio_desc	*desc = dev_get_drvdata(dev);
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	ssize_t			status;

	mutex_lock(&sysfs_lock);

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	if (!test_bit(FLAG_EXPORT, &desc->flags)) {
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		status = -EIO;
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	} else {
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		gpiod_get_direction(desc);
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		status = sprintf(buf, "%s\n",
			test_bit(FLAG_IS_OUT, &desc->flags)
				? "out" : "in");
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	}
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	mutex_unlock(&sysfs_lock);
	return status;
}

static ssize_t gpio_direction_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
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	struct gpio_desc	*desc = dev_get_drvdata(dev);
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	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else if (sysfs_streq(buf, "high"))
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		status = gpiod_direction_output_raw(desc, 1);
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	else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
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		status = gpiod_direction_output_raw(desc, 0);
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	else if (sysfs_streq(buf, "in"))
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		status = gpiod_direction_input(desc);
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	else
		status = -EINVAL;

	mutex_unlock(&sysfs_lock);
	return status ? : size;
}

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static /* const */ DEVICE_ATTR(direction, 0644,
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		gpio_direction_show, gpio_direction_store);

static ssize_t gpio_value_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
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	struct gpio_desc	*desc = dev_get_drvdata(dev);
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	ssize_t			status;

	mutex_lock(&sysfs_lock);

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	if (!test_bit(FLAG_EXPORT, &desc->flags))
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		status = -EIO;
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	else
		status = sprintf(buf, "%d\n", gpiod_get_value_cansleep(desc));
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	mutex_unlock(&sysfs_lock);
	return status;
}

static ssize_t gpio_value_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
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	struct gpio_desc	*desc = dev_get_drvdata(dev);
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	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else if (!test_bit(FLAG_IS_OUT, &desc->flags))
		status = -EPERM;
	else {
		long		value;

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		status = kstrtol(buf, 0, &value);
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		if (status == 0) {
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			gpiod_set_value_cansleep(desc, value);
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			status = size;
		}
	}

	mutex_unlock(&sysfs_lock);
	return status;
}

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static const DEVICE_ATTR(value, 0644,
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		gpio_value_show, gpio_value_store);

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static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
{
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	struct kernfs_node	*value_sd = priv;
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	sysfs_notify_dirent(value_sd);
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	return IRQ_HANDLED;
}

static int gpio_setup_irq(struct gpio_desc *desc, struct device *dev,
		unsigned long gpio_flags)
{
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	struct kernfs_node	*value_sd;
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	unsigned long		irq_flags;
	int			ret, irq, id;

	if ((desc->flags & GPIO_TRIGGER_MASK) == gpio_flags)
		return 0;

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	irq = gpiod_to_irq(desc);
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	if (irq < 0)
		return -EIO;

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	id = desc->flags >> ID_SHIFT;
	value_sd = idr_find(&dirent_idr, id);
	if (value_sd)
		free_irq(irq, value_sd);
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	desc->flags &= ~GPIO_TRIGGER_MASK;

	if (!gpio_flags) {
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		gpiod_unlock_as_irq(desc);
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		ret = 0;
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		goto free_id;
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	}

	irq_flags = IRQF_SHARED;
	if (test_bit(FLAG_TRIG_FALL, &gpio_flags))
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		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
			IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
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	if (test_bit(FLAG_TRIG_RISE, &gpio_flags))
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		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
			IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;
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	if (!value_sd) {
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		value_sd = sysfs_get_dirent(dev->kobj.sd, "value");
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		if (!value_sd) {
			ret = -ENODEV;
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			goto err_out;
		}

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		ret = idr_alloc(&dirent_idr, value_sd, 1, 0, GFP_KERNEL);
		if (ret < 0)
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			goto free_sd;
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		id = ret;
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		desc->flags &= GPIO_FLAGS_MASK;
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		desc->flags |= (unsigned long)id << ID_SHIFT;
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		if (desc->flags >> ID_SHIFT != id) {
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			ret = -ERANGE;
			goto free_id;
		}
	}

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	ret = request_any_context_irq(irq, gpio_sysfs_irq, irq_flags,
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				"gpiolib", value_sd);
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	if (ret < 0)
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		goto free_id;
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	ret = gpiod_lock_as_irq(desc);
	if (ret < 0) {
		gpiod_warn(desc, "failed to flag the GPIO for IRQ\n");
		goto free_id;
	}

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	desc->flags |= gpio_flags;
	return 0;

free_id:
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	idr_remove(&dirent_idr, id);
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	desc->flags &= GPIO_FLAGS_MASK;
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free_sd:
	if (value_sd)
		sysfs_put(value_sd);
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err_out:
	return ret;
}

static const struct {
	const char *name;
	unsigned long flags;
} trigger_types[] = {
	{ "none",    0 },
	{ "falling", BIT(FLAG_TRIG_FALL) },
	{ "rising",  BIT(FLAG_TRIG_RISE) },
	{ "both",    BIT(FLAG_TRIG_FALL) | BIT(FLAG_TRIG_RISE) },
};

static ssize_t gpio_edge_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	const struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else {
		int i;

		status = 0;
		for (i = 0; i < ARRAY_SIZE(trigger_types); i++)
			if ((desc->flags & GPIO_TRIGGER_MASK)
					== trigger_types[i].flags) {
				status = sprintf(buf, "%s\n",
						 trigger_types[i].name);
				break;
			}
	}

	mutex_unlock(&sysfs_lock);
	return status;
}

static ssize_t gpio_edge_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;
	int			i;

	for (i = 0; i < ARRAY_SIZE(trigger_types); i++)
		if (sysfs_streq(trigger_types[i].name, buf))
			goto found;
	return -EINVAL;

found:
	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else {
		status = gpio_setup_irq(desc, dev, trigger_types[i].flags);
		if (!status)
			status = size;
	}

	mutex_unlock(&sysfs_lock);

	return status;
}

static DEVICE_ATTR(edge, 0644, gpio_edge_show, gpio_edge_store);

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static int sysfs_set_active_low(struct gpio_desc *desc, struct device *dev,
				int value)
{
	int			status = 0;

	if (!!test_bit(FLAG_ACTIVE_LOW, &desc->flags) == !!value)
		return 0;

	if (value)
		set_bit(FLAG_ACTIVE_LOW, &desc->flags);
	else
		clear_bit(FLAG_ACTIVE_LOW, &desc->flags);

	/* reconfigure poll(2) support if enabled on one edge only */
	if (dev != NULL && (!!test_bit(FLAG_TRIG_RISE, &desc->flags) ^
				!!test_bit(FLAG_TRIG_FALL, &desc->flags))) {
		unsigned long trigger_flags = desc->flags & GPIO_TRIGGER_MASK;

		gpio_setup_irq(desc, dev, 0);
		status = gpio_setup_irq(desc, dev, trigger_flags);
	}

	return status;
}

static ssize_t gpio_active_low_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	const struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else
		status = sprintf(buf, "%d\n",
				!!test_bit(FLAG_ACTIVE_LOW, &desc->flags));

	mutex_unlock(&sysfs_lock);

	return status;
}

static ssize_t gpio_active_low_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags)) {
		status = -EIO;
	} else {
		long		value;

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		status = kstrtol(buf, 0, &value);
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		if (status == 0)
			status = sysfs_set_active_low(desc, dev, value != 0);
	}

	mutex_unlock(&sysfs_lock);

	return status ? : size;
}

static const DEVICE_ATTR(active_low, 0644,
		gpio_active_low_show, gpio_active_low_store);

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static const struct attribute *gpio_attrs[] = {
	&dev_attr_value.attr,
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	&dev_attr_active_low.attr,
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	NULL,
};

static const struct attribute_group gpio_attr_group = {
	.attrs = (struct attribute **) gpio_attrs,
};

/*
 * /sys/class/gpio/gpiochipN/
 *   /base ... matching gpio_chip.base (N)
 *   /label ... matching gpio_chip.label
 *   /ngpio ... matching gpio_chip.ngpio
 */

static ssize_t chip_base_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	const struct gpio_chip	*chip = dev_get_drvdata(dev);

	return sprintf(buf, "%d\n", chip->base);
}
static DEVICE_ATTR(base, 0444, chip_base_show, NULL);

static ssize_t chip_label_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	const struct gpio_chip	*chip = dev_get_drvdata(dev);

	return sprintf(buf, "%s\n", chip->label ? : "");
}
static DEVICE_ATTR(label, 0444, chip_label_show, NULL);

static ssize_t chip_ngpio_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	const struct gpio_chip	*chip = dev_get_drvdata(dev);

	return sprintf(buf, "%u\n", chip->ngpio);
}
static DEVICE_ATTR(ngpio, 0444, chip_ngpio_show, NULL);

static const struct attribute *gpiochip_attrs[] = {
	&dev_attr_base.attr,
	&dev_attr_label.attr,
	&dev_attr_ngpio.attr,
	NULL,
};

static const struct attribute_group gpiochip_attr_group = {
	.attrs = (struct attribute **) gpiochip_attrs,
};

/*
 * /sys/class/gpio/export ... write-only
 *	integer N ... number of GPIO to export (full access)
 * /sys/class/gpio/unexport ... write-only
 *	integer N ... number of GPIO to unexport
 */
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static ssize_t export_store(struct class *class,
				struct class_attribute *attr,
				const char *buf, size_t len)
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{
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	long			gpio;
	struct gpio_desc	*desc;
	int			status;
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	status = kstrtol(buf, 0, &gpio);
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	if (status < 0)
		goto done;

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	desc = gpio_to_desc(gpio);
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	/* reject invalid GPIOs */
	if (!desc) {
		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
		return -EINVAL;
	}
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	/* No extra locking here; FLAG_SYSFS just signifies that the
	 * request and export were done by on behalf of userspace, so
	 * they may be undone on its behalf too.
	 */

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	status = gpiod_request(desc, "sysfs");
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	if (status < 0) {
		if (status == -EPROBE_DEFER)
			status = -ENODEV;
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		goto done;
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	}
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	status = gpiod_export(desc, true);
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	if (status < 0)
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		gpiod_free(desc);
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	else
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		set_bit(FLAG_SYSFS, &desc->flags);
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done:
	if (status)
		pr_debug("%s: status %d\n", __func__, status);
	return status ? : len;
}

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static ssize_t unexport_store(struct class *class,
				struct class_attribute *attr,
				const char *buf, size_t len)
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{
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	long			gpio;
	struct gpio_desc	*desc;
	int			status;
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	status = kstrtol(buf, 0, &gpio);
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	if (status < 0)
		goto done;

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	desc = gpio_to_desc(gpio);
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	/* reject bogus commands (gpio_unexport ignores them) */
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	if (!desc) {
		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
		return -EINVAL;
	}

	status = -EINVAL;
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	/* No extra locking here; FLAG_SYSFS just signifies that the
	 * request and export were done by on behalf of userspace, so
	 * they may be undone on its behalf too.
	 */
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	if (test_and_clear_bit(FLAG_SYSFS, &desc->flags)) {
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		status = 0;
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		gpiod_free(desc);
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	}
done:
	if (status)
		pr_debug("%s: status %d\n", __func__, status);
	return status ? : len;
}

static struct class_attribute gpio_class_attrs[] = {
	__ATTR(export, 0200, NULL, export_store),
	__ATTR(unexport, 0200, NULL, unexport_store),
	__ATTR_NULL,
};

static struct class gpio_class = {
	.name =		"gpio",
	.owner =	THIS_MODULE,

	.class_attrs =	gpio_class_attrs,
};


/**
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 * gpiod_export - export a GPIO through sysfs
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 * @gpio: gpio to make available, already requested
 * @direction_may_change: true if userspace may change gpio direction
 * Context: arch_initcall or later
 *
 * When drivers want to make a GPIO accessible to userspace after they
 * have requested it -- perhaps while debugging, or as part of their
 * public interface -- they may use this routine.  If the GPIO can
 * change direction (some can't) and the caller allows it, userspace
 * will see "direction" sysfs attribute which may be used to change
 * the gpio's direction.  A "value" attribute will always be provided.
 *
 * Returns zero on success, else an error.
 */
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int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
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{
	unsigned long		flags;
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	int			status;
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	const char		*ioname = NULL;
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	struct device		*dev;
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	int			offset;
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	/* can't export until sysfs is available ... */
	if (!gpio_class.p) {
		pr_debug("%s: called too early!\n", __func__);
		return -ENOENT;
	}

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	if (!desc) {
		pr_debug("%s: invalid gpio descriptor\n", __func__);
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		return -EINVAL;
	}
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	mutex_lock(&sysfs_lock);

	spin_lock_irqsave(&gpio_lock, flags);
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	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
	     test_bit(FLAG_EXPORT, &desc->flags)) {
		spin_unlock_irqrestore(&gpio_lock, flags);
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		gpiod_dbg(desc, "%s: unavailable (requested=%d, exported=%d)\n",
				__func__,
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				test_bit(FLAG_REQUESTED, &desc->flags),
				test_bit(FLAG_EXPORT, &desc->flags));
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		status = -EPERM;
		goto fail_unlock;
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	}
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	if (!desc->chip->direction_input || !desc->chip->direction_output)
		direction_may_change = false;
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	spin_unlock_irqrestore(&gpio_lock, flags);

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	offset = gpio_chip_hwgpio(desc);
	if (desc->chip->names && desc->chip->names[offset])
		ioname = desc->chip->names[offset];
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	dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
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			    desc, ioname ? ioname : "gpio%u",
			    desc_to_gpio(desc));
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	if (IS_ERR(dev)) {
		status = PTR_ERR(dev);
		goto fail_unlock;
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	}

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	status = sysfs_create_group(&dev->kobj, &gpio_attr_group);
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	if (status)
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		goto fail_unregister_device;
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	if (direction_may_change) {
		status = device_create_file(dev, &dev_attr_direction);
		if (status)
			goto fail_unregister_device;
	}

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	if (gpiod_to_irq(desc) >= 0 && (direction_may_change ||
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				       !test_bit(FLAG_IS_OUT, &desc->flags))) {
		status = device_create_file(dev, &dev_attr_edge);
		if (status)
			goto fail_unregister_device;
	}
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	set_bit(FLAG_EXPORT, &desc->flags);
	mutex_unlock(&sysfs_lock);
	return 0;

fail_unregister_device:
	device_unregister(dev);
fail_unlock:
	mutex_unlock(&sysfs_lock);
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	gpiod_dbg(desc, "%s: status %d\n", __func__, status);
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	return status;
}
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EXPORT_SYMBOL_GPL(gpiod_export);
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static int match_export(struct device *dev, const void *data)
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{
	return dev_get_drvdata(dev) == data;
}

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/**
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 * gpiod_export_link - create a sysfs link to an exported GPIO node
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 * @dev: device under which to create symlink
 * @name: name of the symlink
 * @gpio: gpio to create symlink to, already exported
 *
 * Set up a symlink from /sys/.../dev/name to /sys/class/gpio/gpioN
 * node. Caller is responsible for unlinking.
 *
 * Returns zero on success, else an error.
 */
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int gpiod_export_link(struct device *dev, const char *name,
		      struct gpio_desc *desc)
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{
	int			status = -EINVAL;

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	if (!desc) {
		pr_warn("%s: invalid GPIO\n", __func__);
		return -EINVAL;
	}
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	mutex_lock(&sysfs_lock);

	if (test_bit(FLAG_EXPORT, &desc->flags)) {
		struct device *tdev;

		tdev = class_find_device(&gpio_class, NULL, desc, match_export);
		if (tdev != NULL) {
			status = sysfs_create_link(&dev->kobj, &tdev->kobj,
						name);
		} else {
			status = -ENODEV;
		}
	}

	mutex_unlock(&sysfs_lock);

	if (status)
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		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
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	return status;
}
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EXPORT_SYMBOL_GPL(gpiod_export_link);
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/**
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 * gpiod_sysfs_set_active_low - set the polarity of gpio sysfs value
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 * @gpio: gpio to change
 * @value: non-zero to use active low, i.e. inverted values
 *
 * Set the polarity of /sys/class/gpio/gpioN/value sysfs attribute.
 * The GPIO does not have to be exported yet.  If poll(2) support has
 * been enabled for either rising or falling edge, it will be
 * reconfigured to follow the new polarity.
 *
 * Returns zero on success, else an error.
 */
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int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value)
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{
	struct device		*dev = NULL;
	int			status = -EINVAL;

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	if (!desc) {
		pr_warn("%s: invalid GPIO\n", __func__);
		return -EINVAL;
	}
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	mutex_lock(&sysfs_lock);

	if (test_bit(FLAG_EXPORT, &desc->flags)) {
		dev = class_find_device(&gpio_class, NULL, desc, match_export);
		if (dev == NULL) {
			status = -ENODEV;
			goto unlock;
		}
	}

	status = sysfs_set_active_low(desc, dev, value);

unlock:
	mutex_unlock(&sysfs_lock);

	if (status)
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		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
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	return status;
}
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EXPORT_SYMBOL_GPL(gpiod_sysfs_set_active_low);
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/**
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 * gpiod_unexport - reverse effect of gpio_export()
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 * @gpio: gpio to make unavailable
 *
 * This is implicit on gpio_free().
 */
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void gpiod_unexport(struct gpio_desc *desc)
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{
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	int			status = 0;
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	struct device		*dev = NULL;
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	if (!desc) {
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		pr_warn("%s: invalid GPIO\n", __func__);
		return;
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	}
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	mutex_lock(&sysfs_lock);

	if (test_bit(FLAG_EXPORT, &desc->flags)) {

		dev = class_find_device(&gpio_class, NULL, desc, match_export);
		if (dev) {
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			gpio_setup_irq(desc, dev, 0);
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			clear_bit(FLAG_EXPORT, &desc->flags);
		} else
			status = -ENODEV;
	}

	mutex_unlock(&sysfs_lock);
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	if (dev) {
		device_unregister(dev);
		put_device(dev);
	}
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	if (status)
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		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
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}
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EXPORT_SYMBOL_GPL(gpiod_unexport);
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static int gpiochip_export(struct gpio_chip *chip)
{
	int		status;
	struct device	*dev;

	/* Many systems register gpio chips for SOC support very early,
	 * before driver model support is available.  In those cases we
	 * export this later, in gpiolib_sysfs_init() ... here we just
	 * verify that _some_ field of gpio_class got initialized.
	 */
	if (!gpio_class.p)
		return 0;

	/* use chip->base for the ID; it's already known to be unique */
	mutex_lock(&sysfs_lock);
	dev = device_create(&gpio_class, chip->dev, MKDEV(0, 0), chip,
				"gpiochip%d", chip->base);
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	if (!IS_ERR(dev)) {
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		status = sysfs_create_group(&dev->kobj,
				&gpiochip_attr_group);
	} else
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		status = PTR_ERR(dev);
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	chip->exported = (status == 0);
	mutex_unlock(&sysfs_lock);

	if (status) {
		unsigned long	flags;
		unsigned	gpio;

		spin_lock_irqsave(&gpio_lock, flags);
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		gpio = 0;
		while (gpio < chip->ngpio)
			chip->desc[gpio++].chip = NULL;
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		spin_unlock_irqrestore(&gpio_lock, flags);

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		chip_dbg(chip, "%s: status %d\n", __func__, status);
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	}

	return status;
}

static void gpiochip_unexport(struct gpio_chip *chip)
{
	int			status;
	struct device		*dev;

	mutex_lock(&sysfs_lock);
	dev = class_find_device(&gpio_class, NULL, chip, match_export);
	if (dev) {
		put_device(dev);
		device_unregister(dev);
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		chip->exported = false;
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		status = 0;
	} else
		status = -ENODEV;
	mutex_unlock(&sysfs_lock);

	if (status)
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		chip_dbg(chip, "%s: status %d\n", __func__, status);
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}

static int __init gpiolib_sysfs_init(void)
{
	int		status;
	unsigned long	flags;
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	struct gpio_chip *chip;
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	status = class_register(&gpio_class);
	if (status < 0)
		return status;

	/* Scan and register the gpio_chips which registered very
	 * early (e.g. before the class_register above was called).
	 *
	 * We run before arch_initcall() so chip->dev nodes can have
	 * registered, and so arch_initcall() can always gpio_export().
	 */
	spin_lock_irqsave(&gpio_lock, flags);
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	list_for_each_entry(chip, &gpio_chips, list) {
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		if (!chip || chip->exported)
			continue;

		spin_unlock_irqrestore(&gpio_lock, flags);
		status = gpiochip_export(chip);
		spin_lock_irqsave(&gpio_lock, flags);
	}
	spin_unlock_irqrestore(&gpio_lock, flags);


	return status;
}
postcore_initcall(gpiolib_sysfs_init);

#else
static inline int gpiochip_export(struct gpio_chip *chip)
{
	return 0;
}

static inline void gpiochip_unexport(struct gpio_chip *chip)
{
}

#endif /* CONFIG_GPIO_SYSFS */

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/*
 * Add a new chip to the global chips list, keeping the list of chips sorted
 * by base order.
 *
 * Return -EBUSY if the new chip overlaps with some other chip's integer
 * space.
 */
static int gpiochip_add_to_list(struct gpio_chip *chip)
{
	struct list_head *pos = &gpio_chips;
	struct gpio_chip *_chip;
	int err = 0;

	/* find where to insert our chip */
	list_for_each(pos, &gpio_chips) {
		_chip = list_entry(pos, struct gpio_chip, list);
		/* shall we insert before _chip? */
		if (_chip->base >= chip->base + chip->ngpio)
			break;
	}

	/* are we stepping on the chip right before? */
	if (pos != &gpio_chips && pos->prev != &gpio_chips) {
		_chip = list_entry(pos->prev, struct gpio_chip, list);
		if (_chip->base + _chip->ngpio > chip->base) {
			dev_err(chip->dev,
			       "GPIO integer space overlap, cannot add chip\n");
			err = -EBUSY;
		}
	}

	if (!err)
		list_add_tail(&chip->list, pos);

	return err;
}

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/**
 * 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.
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 *
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 * When gpiochip_add() is called very early during boot, so that GPIOs
 * can be freely used, the chip->dev device must be registered before
 * the gpio framework's arch_initcall().  Otherwise sysfs initialization
 * for GPIOs will fail rudely.
 *
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 * If chip->base is negative, this requests dynamic assignment of
 * a range of valid GPIOs.
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 */
int gpiochip_add(struct gpio_chip *chip)
{
	unsigned long	flags;
	int		status = 0;
	unsigned	id;
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	int		base = chip->base;