// SPDX-License-Identifier: GPL-2.0

  #include <linux/idr.h>
  #include <linux/mutex.h>
  #include <linux/device.h>
  #include <linux/sysfs.h>
  #include <linux/gpio/consumer.h>
  #include <linux/gpio/driver.h>
  #include <linux/interrupt.h>
  #include <linux/kdev_t.h>

  #include <linux/slab.h>

  #include <linux/ctype.h>

  
  #include "gpiolib.h"

  #include "gpiolib-sysfs.h"

  #define GPIO_IRQF_TRIGGER_FALLING	BIT(0)
  #define GPIO_IRQF_TRIGGER_RISING	BIT(1)
  #define GPIO_IRQF_TRIGGER_BOTH		(GPIO_IRQF_TRIGGER_FALLING | \
  					 GPIO_IRQF_TRIGGER_RISING)

  struct gpiod_data {
  	struct gpio_desc *desc;

  
  	struct mutex mutex;

  	struct kernfs_node *value_kn;

  	int irq;

  	unsigned char irq_flags;

  
  	bool direction_can_change;

  };

  /*
   * Lock to serialise gpiod export and unexport, and prevent re-export of
   * gpiod whose chip is being unregistered.

   */
  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
   *   /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"
   *   /active_low
   *      * configures polarity of /value
   *      * is read/write as zero/nonzero
   *      * also affects existing and subsequent "falling" and "rising"
   *        /edge configuration
   */

  static ssize_t direction_show(struct device *dev,

  		struct device_attribute *attr, char *buf)
  {

  	struct gpiod_data *data = dev_get_drvdata(dev);
  	struct gpio_desc *desc = data->desc;

  	ssize_t			status;

  	mutex_lock(&data->mutex);

  	gpiod_get_direction(desc);
  	status = sprintf(buf, "%s
  ",

  			test_bit(FLAG_IS_OUT, &desc->flags)
  				? "out" : "in");

  	mutex_unlock(&data->mutex);

  	return status;
  }

  static ssize_t direction_store(struct device *dev,

  		struct device_attribute *attr, const char *buf, size_t size)
  {

  	struct gpiod_data *data = dev_get_drvdata(dev);
  	struct gpio_desc *desc = data->desc;

  	ssize_t			status;

  	mutex_lock(&data->mutex);

  	if (sysfs_streq(buf, "high"))

  		status = gpiod_direction_output_raw(desc, 1);
  	else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
  		status = gpiod_direction_output_raw(desc, 0);
  	else if (sysfs_streq(buf, "in"))
  		status = gpiod_direction_input(desc);
  	else
  		status = -EINVAL;

  	mutex_unlock(&data->mutex);

  	return status ? : size;
  }

  static DEVICE_ATTR_RW(direction);

  static ssize_t value_show(struct device *dev,

  		struct device_attribute *attr, char *buf)
  {

  	struct gpiod_data *data = dev_get_drvdata(dev);
  	struct gpio_desc *desc = data->desc;

  	ssize_t			status;

  	mutex_lock(&data->mutex);

  	status = gpiod_get_value_cansleep(desc);
  	if (status < 0)
  		goto err;

  	buf[0] = '0' + status;
  	buf[1] = '
  ';
  	status = 2;

  err:

  	mutex_unlock(&data->mutex);

  	return status;
  }

  static ssize_t value_store(struct device *dev,

  		struct device_attribute *attr, const char *buf, size_t size)
  {

  	struct gpiod_data *data = dev_get_drvdata(dev);
  	struct gpio_desc *desc = data->desc;

  	ssize_t status = 0;

  	mutex_lock(&data->mutex);

  	if (!test_bit(FLAG_IS_OUT, &desc->flags)) {

  		status = -EPERM;

  	} else {

  		long		value;

  		if (size <= 2 && isdigit(buf[0]) &&
  		    (size == 1 || buf[1] == '
  '))
  			value = buf[0] - '0';
  		else
  			status = kstrtol(buf, 0, &value);

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

  	mutex_unlock(&data->mutex);

  	return status;
  }

  static DEVICE_ATTR_PREALLOC(value, S_IWUSR | S_IRUGO, value_show, value_store);

  
  static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
  {

  	struct gpiod_data *data = priv;
  
  	sysfs_notify_dirent(data->value_kn);

  	return IRQ_HANDLED;
  }

  /* Caller holds gpiod-data mutex. */

  static int gpio_sysfs_request_irq(struct device *dev, unsigned char flags)

  {

  	struct gpiod_data	*data = dev_get_drvdata(dev);
  	struct gpio_desc	*desc = data->desc;

  	unsigned long		irq_flags;

  	int			ret;

  	data->irq = gpiod_to_irq(desc);
  	if (data->irq < 0)

  		return -EIO;

  	data->value_kn = sysfs_get_dirent(dev->kobj.sd, "value");
  	if (!data->value_kn)
  		return -ENODEV;

  
  	irq_flags = IRQF_SHARED;

  	if (flags & GPIO_IRQF_TRIGGER_FALLING)

  		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
  			IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;

  	if (flags & GPIO_IRQF_TRIGGER_RISING)

  		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
  			IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;

  	/*
  	 * FIXME: This should be done in the irq_request_resources callback
  	 *        when the irq is requested, but a few drivers currently fail
  	 *        to do so.
  	 *
  	 *        Remove this redundant call (along with the corresponding
  	 *        unlock) when those drivers have been fixed.
  	 */

  	ret = gpiochip_lock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));

  	if (ret < 0)

  		goto err_put_kn;

  	ret = request_any_context_irq(data->irq, gpio_sysfs_irq, irq_flags,

  				"gpiolib", data);

  	if (ret < 0)
  		goto err_unlock;

  	data->irq_flags = flags;

  	return 0;

  err_unlock:

  	gpiochip_unlock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));

  err_put_kn:
  	sysfs_put(data->value_kn);

  	return ret;
  }

  /*
   * Caller holds gpiod-data mutex (unless called after class-device
   * deregistration).
   */

  static void gpio_sysfs_free_irq(struct device *dev)
  {
  	struct gpiod_data *data = dev_get_drvdata(dev);
  	struct gpio_desc *desc = data->desc;

  	data->irq_flags = 0;

  	free_irq(data->irq, data);

  	gpiochip_unlock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));

  	sysfs_put(data->value_kn);
  }

  static const struct {
  	const char *name;

  	unsigned char flags;

  } trigger_types[] = {
  	{ "none",    0 },

  	{ "falling", GPIO_IRQF_TRIGGER_FALLING },
  	{ "rising",  GPIO_IRQF_TRIGGER_RISING },
  	{ "both",    GPIO_IRQF_TRIGGER_BOTH },

  };

  static ssize_t edge_show(struct device *dev,

  		struct device_attribute *attr, char *buf)
  {

  	struct gpiod_data *data = dev_get_drvdata(dev);

  	ssize_t	status = 0;
  	int i;

  	mutex_lock(&data->mutex);

  	for (i = 0; i < ARRAY_SIZE(trigger_types); i++) {

  		if (data->irq_flags == trigger_types[i].flags) {

  			status = sprintf(buf, "%s
  ", trigger_types[i].name);
  			break;
  		}

  	}

  	mutex_unlock(&data->mutex);

  	return status;
  }

  static ssize_t edge_store(struct device *dev,

  		struct device_attribute *attr, const char *buf, size_t size)
  {

  	struct gpiod_data *data = dev_get_drvdata(dev);

  	unsigned char flags;

  	ssize_t	status = size;

  	int i;

  	for (i = 0; i < ARRAY_SIZE(trigger_types); i++) {

  		if (sysfs_streq(trigger_types[i].name, buf))

  			break;
  	}
  
  	if (i == ARRAY_SIZE(trigger_types))
  		return -EINVAL;

  	flags = trigger_types[i].flags;

  	mutex_lock(&data->mutex);

  	if (flags == data->irq_flags) {

  		status = size;
  		goto out_unlock;
  	}

  	if (data->irq_flags)

  		gpio_sysfs_free_irq(dev);
  
  	if (flags) {
  		status = gpio_sysfs_request_irq(dev, flags);
  		if (!status)
  			status = size;
  	}

  out_unlock:

  	mutex_unlock(&data->mutex);

  
  	return status;
  }

  static DEVICE_ATTR_RW(edge);

  /* Caller holds gpiod-data mutex. */

  static int gpio_sysfs_set_active_low(struct device *dev, int value)

  {

  	struct gpiod_data	*data = dev_get_drvdata(dev);
  	struct gpio_desc	*desc = data->desc;

  	int			status = 0;

  	unsigned int		flags = data->irq_flags;

  
  	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 (flags == GPIO_IRQF_TRIGGER_FALLING ||
  					flags == GPIO_IRQF_TRIGGER_RISING) {

  		gpio_sysfs_free_irq(dev);

  		status = gpio_sysfs_request_irq(dev, flags);

  	}
  
  	return status;
  }

  static ssize_t active_low_show(struct device *dev,

  		struct device_attribute *attr, char *buf)
  {

  	struct gpiod_data *data = dev_get_drvdata(dev);
  	struct gpio_desc *desc = data->desc;

  	ssize_t			status;

  	mutex_lock(&data->mutex);

  	status = sprintf(buf, "%d
  ",

  				!!test_bit(FLAG_ACTIVE_LOW, &desc->flags));

  	mutex_unlock(&data->mutex);

  
  	return status;
  }

  static ssize_t active_low_store(struct device *dev,

  		struct device_attribute *attr, const char *buf, size_t size)
  {

  	struct gpiod_data	*data = dev_get_drvdata(dev);

  	ssize_t			status;

  	long			value;

  	mutex_lock(&data->mutex);

  	status = kstrtol(buf, 0, &value);
  	if (status == 0)

  		status = gpio_sysfs_set_active_low(dev, value);

  	mutex_unlock(&data->mutex);

  
  	return status ? : size;
  }

  static DEVICE_ATTR_RW(active_low);

  static umode_t gpio_is_visible(struct kobject *kobj, struct attribute *attr,
  			       int n)
  {

  	struct device *dev = kobj_to_dev(kobj);

  	struct gpiod_data *data = dev_get_drvdata(dev);
  	struct gpio_desc *desc = data->desc;

  	umode_t mode = attr->mode;

  	bool show_direction = data->direction_can_change;

  
  	if (attr == &dev_attr_direction.attr) {
  		if (!show_direction)
  			mode = 0;
  	} else if (attr == &dev_attr_edge.attr) {
  		if (gpiod_to_irq(desc) < 0)
  			mode = 0;
  		if (!show_direction && test_bit(FLAG_IS_OUT, &desc->flags))
  			mode = 0;
  	}
  
  	return mode;
  }

  static struct attribute *gpio_attrs[] = {

  	&dev_attr_direction.attr,
  	&dev_attr_edge.attr,

  	&dev_attr_value.attr,
  	&dev_attr_active_low.attr,
  	NULL,
  };

  
  static const struct attribute_group gpio_group = {
  	.attrs = gpio_attrs,
  	.is_visible = gpio_is_visible,
  };
  
  static const struct attribute_group *gpio_groups[] = {
  	&gpio_group,
  	NULL
  };

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

  static ssize_t base_show(struct device *dev,

  			       struct device_attribute *attr, char *buf)
  {
  	const struct gpio_chip	*chip = dev_get_drvdata(dev);
  
  	return sprintf(buf, "%d
  ", chip->base);
  }

  static DEVICE_ATTR_RO(base);

  static ssize_t label_show(struct device *dev,

  			       struct device_attribute *attr, char *buf)
  {
  	const struct gpio_chip	*chip = dev_get_drvdata(dev);
  
  	return sprintf(buf, "%s
  ", chip->label ? : "");
  }

  static DEVICE_ATTR_RO(label);

  static ssize_t ngpio_show(struct device *dev,

  			       struct device_attribute *attr, char *buf)
  {
  	const struct gpio_chip	*chip = dev_get_drvdata(dev);
  
  	return sprintf(buf, "%u
  ", chip->ngpio);
  }

  static DEVICE_ATTR_RO(ngpio);

  static struct attribute *gpiochip_attrs[] = {

  	&dev_attr_base.attr,
  	&dev_attr_label.attr,
  	&dev_attr_ngpio.attr,
  	NULL,
  };

  ATTRIBUTE_GROUPS(gpiochip);

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

  	desc = gpio_to_desc(gpio);

  	/* reject invalid GPIOs */
  	if (!desc) {
  		pr_warn("%s: invalid GPIO %ld
  ", __func__, gpio);
  		return -EINVAL;
  	}
  
  	/* 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.
  	 */
  
  	status = gpiod_request(desc, "sysfs");
  	if (status < 0) {
  		if (status == -EPROBE_DEFER)
  			status = -ENODEV;
  		goto done;
  	}

  
  	status = gpiod_set_transitory(desc, false);
  	if (!status) {
  		status = gpiod_export(desc, true);
  		if (status < 0)
  			gpiod_free(desc);
  		else
  			set_bit(FLAG_SYSFS, &desc->flags);
  	}

  
  done:
  	if (status)
  		pr_debug("%s: status %d
  ", __func__, status);
  	return status ? : len;
  }

  static CLASS_ATTR_WO(export);

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

  	desc = gpio_to_desc(gpio);

  	/* reject bogus commands (gpio_unexport ignores them) */
  	if (!desc) {
  		pr_warn("%s: invalid GPIO %ld
  ", __func__, gpio);
  		return -EINVAL;
  	}
  
  	status = -EINVAL;
  
  	/* 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.
  	 */
  	if (test_and_clear_bit(FLAG_SYSFS, &desc->flags)) {
  		status = 0;
  		gpiod_free(desc);
  	}
  done:
  	if (status)
  		pr_debug("%s: status %d
  ", __func__, status);
  	return status ? : len;
  }

  static CLASS_ATTR_WO(unexport);

  static struct attribute *gpio_class_attrs[] = {
  	&class_attr_export.attr,
  	&class_attr_unexport.attr,
  	NULL,

  };

  ATTRIBUTE_GROUPS(gpio_class);

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

  	.class_groups = gpio_class_groups,

  };
  
  
  /**
   * gpiod_export - export a GPIO through sysfs

   * @desc: 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.
   */
  int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
  {

  	struct gpio_chip	*chip;

  	struct gpio_device	*gdev;

  	struct gpiod_data	*data;

  	unsigned long		flags;
  	int			status;
  	const char		*ioname = NULL;
  	struct device		*dev;
  	int			offset;
  
  	/* can't export until sysfs is available ... */
  	if (!gpio_class.p) {
  		pr_debug("%s: called too early!
  ", __func__);
  		return -ENOENT;
  	}
  
  	if (!desc) {
  		pr_debug("%s: invalid gpio descriptor
  ", __func__);
  		return -EINVAL;
  	}

  	gdev = desc->gdev;
  	chip = gdev->chip;

  	mutex_lock(&sysfs_lock);

  	/* check if chip is being removed */

  	if (!chip || !gdev->mockdev) {

  		status = -ENODEV;

  		goto err_unlock;

  	}

  	spin_lock_irqsave(&gpio_lock, flags);
  	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
  	     test_bit(FLAG_EXPORT, &desc->flags)) {
  		spin_unlock_irqrestore(&gpio_lock, flags);
  		gpiod_dbg(desc, "%s: unavailable (requested=%d, exported=%d)
  ",
  				__func__,
  				test_bit(FLAG_REQUESTED, &desc->flags),
  				test_bit(FLAG_EXPORT, &desc->flags));
  		status = -EPERM;

  		goto err_unlock;

  	}

  	spin_unlock_irqrestore(&gpio_lock, flags);

  	data = kzalloc(sizeof(*data), GFP_KERNEL);
  	if (!data) {
  		status = -ENOMEM;
  		goto err_unlock;
  	}
  
  	data->desc = desc;

  	mutex_init(&data->mutex);

  	if (chip->direction_input && chip->direction_output)
  		data->direction_can_change = direction_may_change;
  	else
  		data->direction_can_change = false;

  	offset = gpio_chip_hwgpio(desc);

  	if (chip->names && chip->names[offset])
  		ioname = chip->names[offset];

  	dev = device_create_with_groups(&gpio_class, &gdev->dev,

  					MKDEV(0, 0), data, gpio_groups,

  					ioname ? ioname : "gpio%u",
  					desc_to_gpio(desc));

  	if (IS_ERR(dev)) {
  		status = PTR_ERR(dev);

  		goto err_free_data;

  	}

  	set_bit(FLAG_EXPORT, &desc->flags);
  	mutex_unlock(&sysfs_lock);
  	return 0;

  err_free_data:
  	kfree(data);
  err_unlock:

  	mutex_unlock(&sysfs_lock);
  	gpiod_dbg(desc, "%s: status %d
  ", __func__, status);
  	return status;
  }
  EXPORT_SYMBOL_GPL(gpiod_export);

  static int match_export(struct device *dev, const void *desc)

  {

  	struct gpiod_data *data = dev_get_drvdata(dev);
  
  	return data->desc == desc;

  }
  
  /**
   * gpiod_export_link - create a sysfs link to an exported GPIO node
   * @dev: device under which to create symlink
   * @name: name of the symlink

   * @desc: 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.
   */
  int gpiod_export_link(struct device *dev, const char *name,
  		      struct gpio_desc *desc)
  {

  	struct device *cdev;
  	int ret;

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

  	cdev = class_find_device(&gpio_class, NULL, desc, match_export);
  	if (!cdev)
  		return -ENODEV;

  	ret = sysfs_create_link(&dev->kobj, &cdev->kobj, name);
  	put_device(cdev);

  	return ret;

  }
  EXPORT_SYMBOL_GPL(gpiod_export_link);
  
  /**

   * gpiod_unexport - reverse effect of gpiod_export()

   * @desc: GPIO to make unavailable

   *

   * This is implicit on gpiod_free().

   */
  void gpiod_unexport(struct gpio_desc *desc)
  {

  	struct gpiod_data *data;
  	struct device *dev;

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

  	if (!test_bit(FLAG_EXPORT, &desc->flags))
  		goto err_unlock;

  	dev = class_find_device(&gpio_class, NULL, desc, match_export);
  	if (!dev)
  		goto err_unlock;
  
  	data = dev_get_drvdata(dev);

  	clear_bit(FLAG_EXPORT, &desc->flags);
  
  	device_unregister(dev);
  
  	/*
  	 * Release irq after deregistration to prevent race with edge_store.
  	 */

  	if (data->irq_flags)

  		gpio_sysfs_free_irq(dev);

  
  	mutex_unlock(&sysfs_lock);

  	put_device(dev);
  	kfree(data);

  	return;
  
  err_unlock:
  	mutex_unlock(&sysfs_lock);

  }
  EXPORT_SYMBOL_GPL(gpiod_unexport);

  int gpiochip_sysfs_register(struct gpio_device *gdev)

  {

  	struct device	*dev;

  	struct device	*parent;

  	struct gpio_chip *chip = gdev->chip;

  	/*
  	 * Many systems add gpio chips for SOC support very early,

  	 * before driver model support is available.  In those cases we

  	 * register later, in gpiolib_sysfs_init() ... here we just

  	 * verify that _some_ field of gpio_class got initialized.
  	 */
  	if (!gpio_class.p)
  		return 0;

  	/*
  	 * For sysfs backward compatibility we need to preserve this
  	 * preferred parenting to the gpio_chip parent field, if set.
  	 */
  	if (chip->parent)
  		parent = chip->parent;
  	else
  		parent = &gdev->dev;

  	/* use chip->base for the ID; it's already known to be unique */

  	dev = device_create_with_groups(&gpio_class, parent, MKDEV(0, 0), chip,
  					gpiochip_groups, GPIOCHIP_NAME "%d",
  					chip->base);

  	if (IS_ERR(dev))

  		return PTR_ERR(dev);

  
  	mutex_lock(&sysfs_lock);

  	gdev->mockdev = dev;

  	mutex_unlock(&sysfs_lock);

  	return 0;

  }

  void gpiochip_sysfs_unregister(struct gpio_device *gdev)

  {

  	struct gpio_desc *desc;

  	struct gpio_chip *chip = gdev->chip;

  	unsigned int i;

  	if (!gdev->mockdev)

  		return;

  	device_unregister(gdev->mockdev);

  
  	/* prevent further gpiod exports */
  	mutex_lock(&sysfs_lock);

  	gdev->mockdev = NULL;

  	mutex_unlock(&sysfs_lock);

  
  	/* unregister gpiod class devices owned by sysfs */
  	for (i = 0; i < chip->ngpio; i++) {

  		desc = &gdev->descs[i];

  		if (test_and_clear_bit(FLAG_SYSFS, &desc->flags))
  			gpiod_free(desc);
  	}

  }
  
  static int __init gpiolib_sysfs_init(void)
  {
  	int		status;
  	unsigned long	flags;

  	struct gpio_device *gdev;

  
  	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);

  	list_for_each_entry(gdev, &gpio_devices, list) {

  		if (gdev->mockdev)

  			continue;

  		/*

  		 * TODO we yield gpio_lock here because
  		 * gpiochip_sysfs_register() acquires a mutex. This is unsafe
  		 * and needs to be fixed.

  		 *
  		 * Also it would be nice to use gpiochip_find() here so we
  		 * can keep gpio_chips local to gpiolib.c, but the yield of
  		 * gpio_lock prevents us from doing this.
  		 */

  		spin_unlock_irqrestore(&gpio_lock, flags);

  		status = gpiochip_sysfs_register(gdev);

  		spin_lock_irqsave(&gpio_lock, flags);
  	}
  	spin_unlock_irqrestore(&gpio_lock, flags);

  	return status;
  }
  postcore_initcall(gpiolib_sysfs_init);