gpiolib.c

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#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/spinlock.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>
#include <linux/gpio.h>
#include <linux/of_gpio.h>
#include <linux/idr.h>
#include <linux/slab.h>

#define CREATE_TRACE_POINTS
#include <trace/events/gpio.h>

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


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

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

struct gpio_desc {
    struct gpio_chip    *chip;
    unsigned long       flags;
/* flag symbols are bit numbers */
#define FLAG_REQUESTED  0
#define FLAG_IS_OUT 1
#define FLAG_RESERVED   2
#define FLAG_EXPORT 3   /* protected by sysfs_lock */
#define FLAG_SYSFS  4   /* exported via /sys/class/gpio/control */
#define FLAG_TRIG_FALL  5   /* trigger on falling edge */
#define FLAG_TRIG_RISE  6   /* trigger on rising edge */
#define FLAG_ACTIVE_LOW 7   /* sysfs value has active low */
#define FLAG_OPEN_DRAIN 8   /* Gpio is open drain type */
#define FLAG_OPEN_SOURCE 9  /* Gpio is open source type */

#define ID_SHIFT    16  /* add new flags before this one */

#define GPIO_FLAGS_MASK     ((1 << ID_SHIFT) - 1)
#define GPIO_TRIGGER_MASK   (BIT(FLAG_TRIG_FALL) | BIT(FLAG_TRIG_RISE))

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

#ifdef CONFIG_GPIO_SYSFS
static DEFINE_IDR(dirent_idr);
#endif

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

/* Warn when drivers omit gpio_request() calls -- legal but ill-advised
 * when setting direction, and otherwise illegal.  Until board setup code
 * and drivers use explicit requests everywhere (which won't happen when
 * those calls have no teeth) we can't avoid autorequesting.  This nag
 * message should motivate switching to explicit requests... so should
 * the weaker cleanup after faults, compared to gpio_request().
 *
 * 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.
 */
static int gpio_ensure_requested(struct gpio_desc *desc, unsigned offset)
{
    const struct gpio_chip *chip = desc->chip;
    const int gpio = chip->base + offset;

    if (WARN(test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0,
            "autorequest GPIO-%d\n", gpio)) {
        if (!try_module_get(chip->owner)) {
            pr_err("GPIO-%d: module can't be gotten \n", gpio);
            clear_bit(FLAG_REQUESTED, &desc->flags);
            /* lose */
            return -EIO;
        }
        desc_set_label(desc, "[auto]");
        /* caller must chip->request() w/o spinlock */
        if (chip->request)
            return 1;
    }
    return 0;
}

/* caller holds gpio_lock *OR* gpio is marked as requested */
struct gpio_chip *gpio_to_chip(unsigned gpio)
{
    return gpio_desc[gpio].chip;
}

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

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

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

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

int __init gpiochip_reserve(int start, int ngpio)
{
    int ret = 0;
    unsigned long flags;
    int i;

    if (!gpio_is_valid(start) || !gpio_is_valid(start + ngpio - 1))
        return -EINVAL;

    spin_lock_irqsave(&gpio_lock, flags);

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

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

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

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

    return ret;
}

#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
 *   /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)
{
    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, "%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)
{
    const struct gpio_desc  *desc = dev_get_drvdata(dev);
    unsigned        gpio = desc - gpio_desc;
    ssize_t         status;

    mutex_lock(&sysfs_lock);

    if (!test_bit(FLAG_EXPORT, &desc->flags))
        status = -EIO;
    else if (sysfs_streq(buf, "high"))
        status = gpio_direction_output(gpio, 1);
    else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
        status = gpio_direction_output(gpio, 0);
    else if (sysfs_streq(buf, "in"))
        status = gpio_direction_input(gpio);
    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)
{
    const struct gpio_desc  *desc = dev_get_drvdata(dev);
    unsigned        gpio = desc - gpio_desc;
    ssize_t         status;

    mutex_lock(&sysfs_lock);

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

        value = !!gpio_get_value_cansleep(gpio);
        if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
            value = !value;

        status = sprintf(buf, "%d\n", value);
    }

    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)
{
    const struct gpio_desc  *desc = dev_get_drvdata(dev);
    unsigned        gpio = desc - gpio_desc;
    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 = strict_strtol(buf, 0, &value);
        if (status == 0) {
            if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
                value = !value;
            gpio_set_value_cansleep(gpio, value != 0);
            status = size;
        }
    }

    mutex_unlock(&sysfs_lock);
    return status;
}

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

static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
{
    struct sysfs_dirent *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 sysfs_dirent *value_sd;
    unsigned long       irq_flags;
    int         ret, irq, id;

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

    irq = gpio_to_irq(desc - gpio_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) {
        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, NULL, "value");
        if (!value_sd) {
            ret = -ENODEV;
            goto err_out;
        }

        do {
            ret = -ENOMEM;
            if (idr_pre_get(&dirent_idr, GFP_KERNEL))
                ret = idr_get_new_above(&dirent_idr, value_sd,
                            1, &id);
        } while (ret == -EAGAIN);

        if (ret)
            goto free_sd;

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

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

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

    desc->flags |= gpio_flags;
    return 0;

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 = strict_strtol(buf, 0, &value);
        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);

static const struct attribute *gpio_attrs[] = {
    &dev_attr_value.attr,
    &dev_attr_active_low.attr,
    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
 */
static ssize_t export_store(struct class *class,
                struct class_attribute *attr,
                const char *buf, size_t len)
{
    long    gpio;
    int status;

    status = strict_strtol(buf, 0, &gpio);
    if (status < 0)
        goto done;

    /* 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 = gpio_request(gpio, "sysfs");
    if (status < 0) {
        if (status == -EPROBE_DEFER)
            status = -ENODEV;
        goto done;
    }
    status = gpio_export(gpio, true);
    if (status < 0)
        gpio_free(gpio);
    else
        set_bit(FLAG_SYSFS, &gpio_desc[gpio].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;
    int status;

    status = strict_strtol(buf, 0, &gpio);
    if (status < 0)
        goto done;

    status = -EINVAL;

    /* reject bogus commands (gpio_unexport ignores them) */
    if (!gpio_is_valid(gpio))
        goto done;

    /* 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, &gpio_desc[gpio].flags)) {
        status = 0;
        gpio_free(gpio);
    }
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,
};


int gpio_export(unsigned gpio, bool direction_may_change)
{
    unsigned long       flags;
    struct gpio_desc    *desc;
    int         status = -EINVAL;
    const char      *ioname = NULL;

    /* can't export until sysfs is available ... */
    if (!gpio_class.p) {
        pr_debug("%s: called too early!\n", __func__);
        return -ENOENT;
    }

    if (!gpio_is_valid(gpio))
        goto done;

    mutex_lock(&sysfs_lock);

    spin_lock_irqsave(&gpio_lock, flags);
    desc = &gpio_desc[gpio];
    if (test_bit(FLAG_REQUESTED, &desc->flags)
            && !test_bit(FLAG_EXPORT, &desc->flags)) {
        status = 0;
        if (!desc->chip->direction_input
                || !desc->chip->direction_output)
            direction_may_change = false;
    }
    spin_unlock_irqrestore(&gpio_lock, flags);

    if (desc->chip->names && desc->chip->names[gpio - desc->chip->base])
        ioname = desc->chip->names[gpio - desc->chip->base];

    if (status == 0) {
        struct device   *dev;

        dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
                desc, ioname ? ioname : "gpio%u", gpio);
        if (!IS_ERR(dev)) {
            status = sysfs_create_group(&dev->kobj,
                        &gpio_attr_group);

            if (!status && direction_may_change)
                status = device_create_file(dev,
                        &dev_attr_direction);

            if (!status && gpio_to_irq(gpio) >= 0
                    && (direction_may_change
                        || !test_bit(FLAG_IS_OUT,
                            &desc->flags)))
                status = device_create_file(dev,
                        &dev_attr_edge);

            if (status != 0)
                device_unregister(dev);
        } else
            status = PTR_ERR(dev);
        if (status == 0)
            set_bit(FLAG_EXPORT, &desc->flags);
    }

    mutex_unlock(&sysfs_lock);

done:
    if (status)
        pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);

    return status;
}
EXPORT_SYMBOL_GPL(gpio_export);

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

int gpio_export_link(struct device *dev, const char *name, unsigned gpio)
{
    struct gpio_desc    *desc;
    int         status = -EINVAL;

    if (!gpio_is_valid(gpio))
        goto done;

    mutex_lock(&sysfs_lock);

    desc = &gpio_desc[gpio];

    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);

done:
    if (status)
        pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);

    return status;
}
EXPORT_SYMBOL_GPL(gpio_export_link);


int gpio_sysfs_set_active_low(unsigned gpio, int value)
{
    struct gpio_desc    *desc;
    struct device       *dev = NULL;
    int         status = -EINVAL;

    if (!gpio_is_valid(gpio))
        goto done;

    mutex_lock(&sysfs_lock);

    desc = &gpio_desc[gpio];

    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);

done:
    if (status)
        pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);

    return status;
}
EXPORT_SYMBOL_GPL(gpio_sysfs_set_active_low);

void gpio_unexport(unsigned gpio)
{
    struct gpio_desc    *desc;
    int         status = 0;
    struct device       *dev = NULL;

    if (!gpio_is_valid(gpio)) {
        status = -EINVAL;
        goto done;
    }

    mutex_lock(&sysfs_lock);

    desc = &gpio_desc[gpio];

    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_EXPORT, &desc->flags);
        } else
            status = -ENODEV;
    }

    mutex_unlock(&sysfs_lock);
    if (dev) {
        device_unregister(dev);
        put_device(dev);
    }
done:
    if (status)
        pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
}
EXPORT_SYMBOL_GPL(gpio_unexport);

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);
    if (!IS_ERR(dev)) {
        status = sysfs_create_group(&dev->kobj,
                &gpiochip_attr_group);
    } else
        status = PTR_ERR(dev);
    chip->exported = (status == 0);
    mutex_unlock(&sysfs_lock);

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

        spin_lock_irqsave(&gpio_lock, flags);
        gpio = chip->base;
        while (gpio_desc[gpio].chip == chip)
            gpio_desc[gpio++].chip = NULL;
        spin_unlock_irqrestore(&gpio_lock, flags);

        pr_debug("%s: chip %s status %d\n", __func__,
                chip->label, status);
    }

    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);
        chip->exported = 0;
        status = 0;
    } else
        status = -ENODEV;
    mutex_unlock(&sysfs_lock);

    if (status)
        pr_debug("%s: chip %s status %d\n", __func__,
                chip->label, status);
}

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

    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);
    for (gpio = 0; gpio < ARCH_NR_GPIOS; gpio++) {
        struct gpio_chip    *chip;

        chip = gpio_desc[gpio].chip;
        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 */

int gpiochip_add(struct gpio_chip *chip)
{
    unsigned long   flags;
    int     status = 0;
    unsigned    id;
    int     base = chip->base;

    if ((!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio - 1))
            && base >= 0) {
        status = -EINVAL;
        goto fail;
    }

    spin_lock_irqsave(&gpio_lock, flags);

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

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

            /* REVISIT:  most hardware initializes GPIOs as
             * inputs (often with pullups enabled) so power
             * usage is minimized.  Linux code should set the
             * gpio direction first thing; but until it does,
             * we may expose the wrong direction in sysfs.
             */
            gpio_desc[id].flags = !chip->direction_input
                ? (1 << FLAG_IS_OUT)
                : 0;
        }
    }

    of_gpiochip_add(chip);

unlock:
    spin_unlock_irqrestore(&gpio_lock, flags);

    if (status)
        goto fail;

    status = gpiochip_export(chip);
    if (status)
        goto fail;

    pr_debug("gpiochip_add: registered GPIOs %d to %d on device: %s\n",
        chip->base, chip->base + chip->ngpio - 1,
        chip->label ? : "generic");

    return 0;
fail:
    /* failures here can mean systems won't boot... */
    pr_err("gpiochip_add: gpios %d..%d (%s) failed to register\n",
        chip->base, chip->base + chip->ngpio - 1,
        chip->label ? : "generic");
    return status;
}
EXPORT_SYMBOL_GPL(gpiochip_add);

int gpiochip_remove(struct gpio_chip *chip)
{
    unsigned long   flags;
    int     status = 0;
    unsigned    id;

    spin_lock_irqsave(&gpio_lock, flags);

    of_gpiochip_remove(chip);

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

    spin_unlock_irqrestore(&gpio_lock, flags);

    if (status == 0)
        gpiochip_unexport(chip);

    return status;
}
EXPORT_SYMBOL_GPL(gpiochip_remove);

struct gpio_chip *gpiochip_find(void *data,
                int (*match)(struct gpio_chip *chip,
                         void *data))
{
    struct gpio_chip *chip = NULL;
    unsigned long flags;
    int i;

    spin_lock_irqsave(&gpio_lock, flags);
    for (i = 0; i < ARCH_NR_GPIOS; i++) {
        if (!gpio_desc[i].chip)
            continue;

        if (match(gpio_desc[i].chip, data)) {
            chip = gpio_desc[i].chip;
            break;
        }
    }
    spin_unlock_irqrestore(&gpio_lock, flags);

    return chip;
}
EXPORT_SYMBOL_GPL(gpiochip_find);

/* These "optional" allocation calls help prevent drivers from stomping
 * on each other, and help provide better diagnostics in debugfs.
 * They're called even less than the "set direction" calls.
 */
int gpio_request(unsigned gpio, const char *label)
{
    struct gpio_desc    *desc;
    struct gpio_chip    *chip;
    int         status = -EPROBE_DEFER;
    unsigned long       flags;

    spin_lock_irqsave(&gpio_lock, flags);

    if (!gpio_is_valid(gpio)) {
        status = -EINVAL;
        goto done;
    }
    desc = &gpio_desc[gpio];
    chip = desc->chip;
    if (chip == NULL)
        goto done;

    if (!try_module_get(chip->owner))
        goto done;

    /* NOTE:  gpio_request() can be called in early boot,
     * before IRQs are enabled, for non-sleeping (SOC) GPIOs.
     */

    if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
        desc_set_label(desc, label ? : "?");
        status = 0;
    } else {
        status = -EBUSY;
        module_put(chip->owner);
        goto done;
    }

    if (chip->request) {
        /* chip->request may sleep */
        spin_unlock_irqrestore(&gpio_lock, flags);
        status = chip->request(chip, gpio - chip->base);
        spin_lock_irqsave(&gpio_lock, flags);

        if (status < 0) {
            desc_set_label(desc, NULL);
            module_put(chip->owner);
            clear_bit(FLAG_REQUESTED, &desc->flags);
        }
    }

done:
    if (status)
        pr_debug("gpio_request: gpio-%d (%s) status %d\n",
            gpio, label ? : "?", status);
    spin_unlock_irqrestore(&gpio_lock, flags);
    return status;
}
EXPORT_SYMBOL_GPL(gpio_request);

void gpio_free(unsigned gpio)
{
    unsigned long       flags;
    struct gpio_desc    *desc;
    struct gpio_chip    *chip;

    might_sleep();

    if (!gpio_is_valid(gpio)) {
        WARN_ON(extra_checks);
        return;
    }

    gpio_unexport(gpio);

    spin_lock_irqsave(&gpio_lock, flags);

    desc = &gpio_desc[gpio];
    chip = desc->chip;
    if (chip && test_bit(FLAG_REQUESTED, &desc->flags)) {
        if (chip->free) {
            spin_unlock_irqrestore(&gpio_lock, flags);
            might_sleep_if(chip->can_sleep);
            chip->free(chip, gpio - chip->base);
            spin_lock_irqsave(&gpio_lock, flags);
        }
        desc_set_label(desc, NULL);
        module_put(desc->chip->owner);
        clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
        clear_bit(FLAG_REQUESTED, &desc->flags);
        clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
        clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
    } else
        WARN_ON(extra_checks);

    spin_unlock_irqrestore(&gpio_lock, flags);
}
EXPORT_SYMBOL_GPL(gpio_free);

int gpio_request_one(unsigned gpio, unsigned long flags, const char *label)
{
    int err;

    err = gpio_request(gpio, label);
    if (err)
        return err;

    if (flags & GPIOF_OPEN_DRAIN)
        set_bit(FLAG_OPEN_DRAIN, &gpio_desc[gpio].flags);

    if (flags & GPIOF_OPEN_SOURCE)
        set_bit(FLAG_OPEN_SOURCE, &gpio_desc[gpio].flags);

    if (flags & GPIOF_DIR_IN)
        err = gpio_direction_input(gpio);
    else
        err = gpio_direction_output(gpio,
                (flags & GPIOF_INIT_HIGH) ? 1 : 0);

    if (err)
        goto free_gpio;

    if (flags & GPIOF_EXPORT) {
        err = gpio_export(gpio, flags & GPIOF_EXPORT_CHANGEABLE);
        if (err)
            goto free_gpio;
    }

    return 0;

 free_gpio:
    gpio_free(gpio);
    return err;
}
EXPORT_SYMBOL_GPL(gpio_request_one);

int gpio_request_array(const struct gpio *array, size_t num)
{
    int i, err;

    for (i = 0; i < num; i++, array++) {
        err = gpio_request_one(array->gpio, array->flags, array->label);
        if (err)
            goto err_free;
    }
    return 0;

err_free:
    while (i--)
        gpio_free((--array)->gpio);
    return err;
}
EXPORT_SYMBOL_GPL(gpio_request_array);

void gpio_free_array(const struct gpio *array, size_t num)
{
    while (num--)
        gpio_free((array++)->gpio);
}
EXPORT_SYMBOL_GPL(gpio_free_array);

const char *gpiochip_is_requested(struct gpio_chip *chip, unsigned offset)
{
    unsigned gpio = chip->base + offset;

    if (!gpio_is_valid(gpio) || gpio_desc[gpio].chip != chip)
        return NULL;
    if (test_bit(FLAG_REQUESTED, &gpio_desc[gpio].flags) == 0)
        return NULL;
#ifdef CONFIG_DEBUG_FS
    return gpio_desc[gpio].label;
#else
    return "?";
#endif
}
EXPORT_SYMBOL_GPL(gpiochip_is_requested);


/* Drivers MUST set GPIO direction before making get/set calls.  In
 * some cases this is done in early boot, before IRQs are enabled.
 *
 * As a rule these aren't called more than once (except for drivers
 * using the open-drain emulation idiom) so these are natural places
 * to accumulate extra debugging checks.  Note that we can't (yet)
 * rely on gpio_request() having been called beforehand.
 */

int gpio_direction_input(unsigned gpio)
{
    unsigned long       flags;
    struct gpio_chip    *chip;
    struct gpio_desc    *desc = &gpio_desc[gpio];
    int         status = -EINVAL;

    spin_lock_irqsave(&gpio_lock, flags);

    if (!gpio_is_valid(gpio))
        goto fail;
    chip = desc->chip;
    if (!chip || !chip->get || !chip->direction_input)
        goto fail;
    gpio -= chip->base;
    if (gpio >= chip->ngpio)
        goto fail;
    status = gpio_ensure_requested(desc, gpio);
    if (status < 0)
        goto fail;

    /* now we know the gpio is valid and chip won't vanish */

    spin_unlock_irqrestore(&gpio_lock, flags);

    might_sleep_if(chip->can_sleep);

    if (status) {
        status = chip->request(chip, gpio);
        if (status < 0) {
            pr_debug("GPIO-%d: chip request fail, %d\n",
                chip->base + gpio, status);
            /* and it's not available to anyone else ...
             * gpio_request() is the fully clean solution.
             */
            goto lose;
        }
    }

    status = chip->direction_input(chip, gpio);
    if (status == 0)
        clear_bit(FLAG_IS_OUT, &desc->flags);

    trace_gpio_direction(chip->base + gpio, 1, status);
lose:
    return status;
fail:
    spin_unlock_irqrestore(&gpio_lock, flags);
    if (status)
        pr_debug("%s: gpio-%d status %d\n",
            __func__, gpio, status);
    return status;
}
EXPORT_SYMBOL_GPL(gpio_direction_input);

int gpio_direction_output(unsigned gpio, int value)
{
    unsigned long       flags;
    struct gpio_chip    *chip;
    struct gpio_desc    *desc = &gpio_desc[gpio];
    int         status = -EINVAL;

    /* Open drain pin should not be driven to 1 */
    if (value && test_bit(FLAG_OPEN_DRAIN,  &desc->flags))
        return gpio_direction_input(gpio);

    /* Open source pin should not be driven to 0 */
    if (!value && test_bit(FLAG_OPEN_SOURCE,  &desc->flags))
        return gpio_direction_input(gpio);

    spin_lock_irqsave(&gpio_lock, flags);

    if (!gpio_is_valid(gpio))
        goto fail;
    chip = desc->chip;
    if (!chip || !chip->set || !chip->direction_output)
        goto fail;
    gpio -= chip->base;
    if (gpio >= chip->ngpio)
        goto fail;
    status = gpio_ensure_requested(desc, gpio);
    if (status < 0)
        goto fail;

    /* now we know the gpio is valid and chip won't vanish */

    spin_unlock_irqrestore(&gpio_lock, flags);

    might_sleep_if(chip->can_sleep);

    if (status) {
        status = chip->request(chip, gpio);
        if (status < 0) {
            pr_debug("GPIO-%d: chip request fail, %d\n",
                chip->base + gpio, status);
            /* and it's not available to anyone else ...
             * gpio_request() is the fully clean solution.
             */
            goto lose;
        }
    }

    status = chip->direction_output(chip, gpio, value);
    if (status == 0)
        set_bit(FLAG_IS_OUT, &desc->flags);
    trace_gpio_value(chip->base + gpio, 0, value);
    trace_gpio_direction(chip->base + gpio, 0, status);
lose:
    return status;
fail:
    spin_unlock_irqrestore(&gpio_lock, flags);
    if (status)
        pr_debug("%s: gpio-%d status %d\n",
            __func__, gpio, status);
    return status;
}
EXPORT_SYMBOL_GPL(gpio_direction_output);

int gpio_set_debounce(unsigned gpio, unsigned debounce)
{
    unsigned long       flags;
    struct gpio_chip    *chip;
    struct gpio_desc    *desc = &gpio_desc[gpio];
    int         status = -EINVAL;

    spin_lock_irqsave(&gpio_lock, flags);

    if (!gpio_is_valid(gpio))
        goto fail;
    chip = desc->chip;
    if (!chip || !chip->set || !chip->set_debounce)
        goto fail;
    gpio -= chip->base;
    if (gpio >= chip->ngpio)
        goto fail;
    status = gpio_ensure_requested(desc, gpio);
    if (status < 0)
        goto fail;

    /* now we know the gpio is valid and chip won't vanish */

    spin_unlock_irqrestore(&gpio_lock, flags);

    might_sleep_if(chip->can_sleep);

    return chip->set_debounce(chip, gpio, debounce);

fail:
    spin_unlock_irqrestore(&gpio_lock, flags);
    if (status)
        pr_debug("%s: gpio-%d status %d\n",
            __func__, gpio, status);

    return status;
}
EXPORT_SYMBOL_GPL(gpio_set_debounce);

/* I/O calls are only valid after configuration completed; the relevant
 * "is this a valid GPIO" error checks should already have been done.
 *
 * "Get" operations are often inlinable as reading a pin value register,
 * and masking the relevant bit in that register.
 *
 * When "set" operations are inlinable, they involve writing that mask to
 * one register to set a low value, or a different register to set it high.
 * Otherwise locking is needed, so there may be little value to inlining.
 *
 *------------------------------------------------------------------------
 *
 * IMPORTANT!!!  The hot paths -- get/set value -- assume that callers
 * have requested the GPIO.  That can include implicit requesting by
 * a direction setting call.  Marking a gpio as requested locks its chip
 * in memory, guaranteeing that these table lookups need no more locking
 * and that gpiochip_remove() will fail.
 *
 * REVISIT when debugging, consider adding some instrumentation to ensure
 * that the GPIO was actually requested.
 */

int __gpio_get_value(unsigned gpio)
{
    struct gpio_chip    *chip;
    int value;

    chip = gpio_to_chip(gpio);
    /* Should be using gpio_get_value_cansleep() */
    WARN_ON(chip->can_sleep);
    value = chip->get ? chip->get(chip, gpio - chip->base) : 0;
    trace_gpio_value(gpio, 1, value);
    return value;
}
EXPORT_SYMBOL_GPL(__gpio_get_value);

/*
 *  _gpio_set_open_drain_value() - Set the open drain gpio's value.
 * @gpio: Gpio whose state need to be set.
 * @chip: Gpio chip.
 * @value: Non-zero for setting it HIGH otherise it will set to LOW.
 */
static void _gpio_set_open_drain_value(unsigned gpio,
            struct gpio_chip *chip, int value)
{
    int err = 0;
    if (value) {
        err = chip->direction_input(chip, gpio - chip->base);
        if (!err)
            clear_bit(FLAG_IS_OUT, &gpio_desc[gpio].flags);
    } else {
        err = chip->direction_output(chip, gpio - chip->base, 0);
        if (!err)
            set_bit(FLAG_IS_OUT, &gpio_desc[gpio].flags);
    }
    trace_gpio_direction(gpio, value, err);
    if (err < 0)
        pr_err("%s: Error in set_value for open drain gpio%d err %d\n",
                    __func__, gpio, err);
}

/*
 *  _gpio_set_open_source() - Set the open source gpio's value.
 * @gpio: Gpio whose state need to be set.
 * @chip: Gpio chip.
 * @value: Non-zero for setting it HIGH otherise it will set to LOW.
 */
static void _gpio_set_open_source_value(unsigned gpio,
            struct gpio_chip *chip, int value)
{
    int err = 0;
    if (value) {
        err = chip->direction_output(chip, gpio - chip->base, 1);
        if (!err)
            set_bit(FLAG_IS_OUT, &gpio_desc[gpio].flags);
    } else {
        err = chip->direction_input(chip, gpio - chip->base);
        if (!err)
            clear_bit(FLAG_IS_OUT, &gpio_desc[gpio].flags);
    }
    trace_gpio_direction(gpio, !value, err);
    if (err < 0)
        pr_err("%s: Error in set_value for open source gpio%d err %d\n",
                    __func__, gpio, err);
}


void __gpio_set_value(unsigned gpio, int value)
{
    struct gpio_chip    *chip;

    chip = gpio_to_chip(gpio);
    /* Should be using gpio_set_value_cansleep() */
    WARN_ON(chip->can_sleep);
    trace_gpio_value(gpio, 0, value);
    if (test_bit(FLAG_OPEN_DRAIN,  &gpio_desc[gpio].flags))
        _gpio_set_open_drain_value(gpio, chip, value);
    else if (test_bit(FLAG_OPEN_SOURCE,  &gpio_desc[gpio].flags))
        _gpio_set_open_source_value(gpio, chip, value);
    else
        chip->set(chip, gpio - chip->base, value);
}
EXPORT_SYMBOL_GPL(__gpio_set_value);

int __gpio_cansleep(unsigned gpio)
{
    struct gpio_chip    *chip;

    /* only call this on GPIOs that are valid! */
    chip = gpio_to_chip(gpio);

    return chip->can_sleep;
}
EXPORT_SYMBOL_GPL(__gpio_cansleep);

int __gpio_to_irq(unsigned gpio)
{
    struct gpio_chip    *chip;

    chip = gpio_to_chip(gpio);
    return chip->to_irq ? chip->to_irq(chip, gpio - chip->base) : -ENXIO;
}
EXPORT_SYMBOL_GPL(__gpio_to_irq);



/* There's no value in making it easy to inline GPIO calls that may sleep.
 * Common examples include ones connected to I2C or SPI chips.
 */

int gpio_get_value_cansleep(unsigned gpio)
{
    struct gpio_chip    *chip;
    int value;

    might_sleep_if(extra_checks);
    chip = gpio_to_chip(gpio);
    value = chip->get ? chip->get(chip, gpio - chip->base) : 0;
    trace_gpio_value(gpio, 1, value);
    return value;
}
EXPORT_SYMBOL_GPL(gpio_get_value_cansleep);

void gpio_set_value_cansleep(unsigned gpio, int value)
{
    struct gpio_chip    *chip;

    might_sleep_if(extra_checks);
    chip = gpio_to_chip(gpio);
    trace_gpio_value(gpio, 0, value);
    if (test_bit(FLAG_OPEN_DRAIN,  &gpio_desc[gpio].flags))
        _gpio_set_open_drain_value(gpio, chip, value);
    else if (test_bit(FLAG_OPEN_SOURCE,  &gpio_desc[gpio].flags))
        _gpio_set_open_source_value(gpio, chip, value);
    else
        chip->set(chip, gpio - chip->base, value);
}
EXPORT_SYMBOL_GPL(gpio_set_value_cansleep);


#ifdef CONFIG_DEBUG_FS

static void gpiolib_dbg_show(struct seq_file *s, struct gpio_chip *chip)
{
    unsigned        i;
    unsigned        gpio = chip->base;
    struct gpio_desc    *gdesc = &gpio_desc[gpio];
    int         is_out;

    for (i = 0; i < chip->ngpio; i++, gpio++, gdesc++) {
        if (!test_bit(FLAG_REQUESTED, &gdesc->flags))
            continue;

        is_out = test_bit(FLAG_IS_OUT, &gdesc->flags);
        seq_printf(s, " gpio-%-3d (%-20.20s) %s %s",
            gpio, gdesc->label,
            is_out ? "out" : "in ",
            chip->get
                ? (chip->get(chip, i) ? "hi" : "lo")
                : "?  ");
        seq_printf(s, "\n");
    }
}

static void *gpiolib_seq_start(struct seq_file *s, loff_t *pos)
{
    struct gpio_chip *chip = NULL;
    unsigned int gpio;
    void *ret = NULL;
    loff_t index = 0;

    /* REVISIT this isn't locked against gpio_chip removal ... */

    for (gpio = 0; gpio_is_valid(gpio); gpio++) {
        if (gpio_desc[gpio].chip == chip)
            continue;

        chip = gpio_desc[gpio].chip;
        if (!chip)
            continue;

        if (index++ >= *pos) {
            ret = chip;
            break;
        }
    }

    s->private = "";

    return ret;
}

static void *gpiolib_seq_next(struct seq_file *s, void *v, loff_t *pos)
{
    struct gpio_chip *chip = v;
    unsigned int gpio;
    void *ret = NULL;

    /* skip GPIOs provided by the current chip */
    for (gpio = chip->base + chip->ngpio; gpio_is_valid(gpio); gpio++) {
        chip = gpio_desc[gpio].chip;
        if (chip) {
            ret = chip;
            break;
        }
    }

    s->private = "\n";
    ++*pos;

    return ret;
}

static void gpiolib_seq_stop(struct seq_file *s, void *v)
{
}

static int gpiolib_seq_show(struct seq_file *s, void *v)
{
    struct gpio_chip *chip = v;
    struct device *dev;

    seq_printf(s, "%sGPIOs %d-%d", (char *)s->private,
            chip->base, chip->base + chip->ngpio - 1);
    dev = chip->dev;
    if (dev)
        seq_printf(s, ", %s/%s", dev->bus ? dev->bus->name : "no-bus",
            dev_name(dev));
    if (chip->label)
        seq_printf(s, ", %s", chip->label);
    if (chip->can_sleep)
        seq_printf(s, ", can sleep");
    seq_printf(s, ":\n");

    if (chip->dbg_show)
        chip->dbg_show(s, chip);
    else
        gpiolib_dbg_show(s, chip);

    return 0;
}

static const struct seq_operations gpiolib_seq_ops = {
    .start = gpiolib_seq_start,
    .next = gpiolib_seq_next,
    .stop = gpiolib_seq_stop,
    .show = gpiolib_seq_show,
};

static int gpiolib_open(struct inode *inode, struct file *file)
{
    return seq_open(file, &gpiolib_seq_ops);
}

static const struct file_operations gpiolib_operations = {
    .owner      = THIS_MODULE,
    .open       = gpiolib_open,
    .read       = seq_read,
    .llseek     = seq_lseek,
    .release    = seq_release,
};

static int __init gpiolib_debugfs_init(void)
{
    /* /sys/kernel/debug/gpio */
    (void) debugfs_create_file("gpio", S_IFREG | S_IRUGO,
                NULL, NULL, &gpiolib_operations);
    return 0;
}
subsys_initcall(gpiolib_debugfs_init);

#endif  /* DEBUG_FS */