#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 "gpiolib.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 = sprintf(buf, "%d
  ", gpiod_get_value_cansleep(desc));
  
  	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;
  
  	mutex_lock(&data->mutex);
  
  	if (!test_bit(FLAG_IS_OUT, &desc->flags)) {
  		status = -EPERM;
  	} else {
  		long		value;
  
  		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_RW(value);
  
  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->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->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->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 = container_of(kobj, struct device, 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_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 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 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,
  };
  
  
  /**
   * gpiod_export - export a GPIO through sysfs
   * @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.
   */
  int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
  {
  	struct gpio_chip	*chip;
  	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;
  	}
  
  	chip = desc->chip;
  
  	mutex_lock(&sysfs_lock);
  
  	/* check if chip is being removed */
  	if (!chip || !chip->cdev) {
  		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, chip->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
   * @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.
   */
  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 gpio_export()
   * @gpio: gpio to make unavailable
   *
   * This is implicit on gpio_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_chip *chip)
  {
  	struct device	*dev;
  
  	/*
  	 * 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;
  
  	/* use chip->base for the ID; it's already known to be unique */
  	dev = device_create_with_groups(&gpio_class, chip->dev, MKDEV(0, 0),
  					chip, gpiochip_groups,
  					"gpiochip%d", chip->base);
  	if (IS_ERR(dev))
  		return PTR_ERR(dev);
  
  	mutex_lock(&sysfs_lock);
  	chip->cdev = dev;
  	mutex_unlock(&sysfs_lock);
  
  	return 0;
  }
  
  void gpiochip_sysfs_unregister(struct gpio_chip *chip)
  {
  	struct gpio_desc *desc;
  	unsigned int i;
  
  	if (!chip->cdev)
  		return;
  
  	device_unregister(chip->cdev);
  
  	/* prevent further gpiod exports */
  	mutex_lock(&sysfs_lock);
  	chip->cdev = NULL;
  	mutex_unlock(&sysfs_lock);
  
  	/* unregister gpiod class devices owned by sysfs */
  	for (i = 0; i < chip->ngpio; i++) {
  		desc = &chip->desc[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_chip *chip;
  
  	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(chip, &gpio_chips, list) {
  		if (chip->cdev)
  			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(chip);
  		spin_lock_irqsave(&gpio_lock, flags);
  	}
  	spin_unlock_irqrestore(&gpio_lock, flags);
  
  
  	return status;
  }
  postcore_initcall(gpiolib_sysfs_init);