gpio: sysfs: rename gpiochip registration functions

[linux-2.6/btrfs-unstable.git] / drivers / gpio / gpiolib-sysfs.c

#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 "gpiolib.h"

static DEFINE_IDR(dirent_idr);


/* 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
 *   /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 gpio_direction_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        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 {
                gpiod_get_direction(desc);
                status = sprintf(buf, "%s\n",
                        test_bit(FLAG_IS_OUT, &desc->flags)
                                ? "out" : "in");
        }

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

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

static ssize_t gpio_value_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        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", gpiod_get_value_cansleep(desc));

        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)
{
        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 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(&sysfs_lock);
        return status;
}

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

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

        sysfs_notify_dirent(value_sd);
        return IRQ_HANDLED;
}

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

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

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

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

        desc->flags &= ~GPIO_TRIGGER_MASK;

        if (!gpio_flags) {
                gpiochip_unlock_as_irq(desc->chip, gpio_chip_hwgpio(desc));
                ret = 0;
                goto free_id;
        }

        irq_flags = IRQF_SHARED;
        if (test_bit(FLAG_TRIG_FALL, &gpio_flags))
                irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
                        IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
        if (test_bit(FLAG_TRIG_RISE, &gpio_flags))
                irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
                        IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;

        if (!value_sd) {
                value_sd = sysfs_get_dirent(dev->kobj.sd, "value");
                if (!value_sd) {
                        ret = -ENODEV;
                        goto err_out;
                }

                ret = idr_alloc(&dirent_idr, value_sd, 1, 0, GFP_KERNEL);
                if (ret < 0)
                        goto free_sd;
                id = ret;

                desc->flags &= GPIO_FLAGS_MASK;
                desc->flags |= (unsigned long)id << ID_SHIFT;

                if (desc->flags >> ID_SHIFT != id) {
                        ret = -ERANGE;
                        goto free_id;
                }
        }

        /*
         * 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 free_id;

        ret = request_any_context_irq(irq, gpio_sysfs_irq, irq_flags,
                                "gpiolib", value_sd);
        if (ret < 0)
                goto err_unlock;

        desc->flags |= gpio_flags;
        return 0;

err_unlock:
        gpiochip_unlock_as_irq(desc->chip, gpio_chip_hwgpio(desc));
free_id:
        idr_remove(&dirent_idr, id);
        desc->flags &= GPIO_FLAGS_MASK;
free_sd:
        if (value_sd)
                sysfs_put(value_sd);
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);

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;

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

        mutex_unlock(&sysfs_lock);

        return status ? : size;
}

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

static umode_t gpio_is_visible(struct kobject *kobj, struct attribute *attr,
                               int n)
{
        struct device *dev = container_of(kobj, struct device, kobj);
        struct gpio_desc *desc = dev_get_drvdata(dev);
        umode_t mode = attr->mode;
        bool show_direction = test_bit(FLAG_SYSFS_DIR, &desc->flags);

        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 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 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\n", __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\n", __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\n", __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\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,
};


/**
 * 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;
        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!\n", __func__);
                return -ENOENT;
        }

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

        chip = desc->chip;

        mutex_lock(&sysfs_lock);

        /* check if chip is being removed */
        if (!chip || !chip->cdev) {
                status = -ENODEV;
                goto fail_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)\n",
                                __func__,
                                test_bit(FLAG_REQUESTED, &desc->flags),
                                test_bit(FLAG_EXPORT, &desc->flags));
                status = -EPERM;
                goto fail_unlock;
        }

        if (chip->direction_input && chip->direction_output &&
                        direction_may_change) {
                set_bit(FLAG_SYSFS_DIR, &desc->flags);
        }

        spin_unlock_irqrestore(&gpio_lock, flags);

        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), desc, gpio_groups,
                                        ioname ? ioname : "gpio%u",
                                        desc_to_gpio(desc));
        if (IS_ERR(dev)) {
                status = PTR_ERR(dev);
                goto fail_unlock;
        }

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

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

static int match_export(struct device *dev, const void *data)
{
        return dev_get_drvdata(dev) == data;
}

/**
 * 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)
{
        int                     status = -EINVAL;

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

        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);
                        put_device(tdev);
                } else {
                        status = -ENODEV;
                }
        }

        mutex_unlock(&sysfs_lock);

        if (status)
                gpiod_dbg(desc, "%s: status %d\n", __func__, status);

        return status;
}
EXPORT_SYMBOL_GPL(gpiod_export_link);

/**
 * gpiod_sysfs_set_active_low - set the polarity of gpio sysfs value
 * @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.
 */
int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value)
{
        struct device           *dev = NULL;
        int                     status = -EINVAL;

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

        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);
        put_device(dev);
unlock:
        mutex_unlock(&sysfs_lock);

        if (status)
                gpiod_dbg(desc, "%s: status %d\n", __func__, status);

        return status;
}
EXPORT_SYMBOL_GPL(gpiod_sysfs_set_active_low);

/**
 * 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)
{
        int                     status = 0;
        struct device           *dev = NULL;

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

        mutex_lock(&sysfs_lock);

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

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

        mutex_unlock(&sysfs_lock);

        if (dev) {
                device_unregister(dev);
                put_device(dev);
        }

        if (status)
                gpiod_dbg(desc, "%s: status %d\n", __func__, status);
}
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);