ASoC: TWL4030: Add functionalty to reset the registers

[deliverable/linux.git] / drivers / gpio / gpiolib.c

#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/idr.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 PDESC_ID_SHIFT  16      /* add new flags before this one */

#define GPIO_FLAGS_MASK         ((1 << PDESC_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
struct poll_desc {
        struct work_struct      work;
        struct sysfs_dirent     *value_sd;
};

static struct idr pdesc_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 */
static inline 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;
}

/**
 * gpiochip_reserve() - reserve range of gpios to use with platform code only
 * @start: starting gpio number
 * @ngpio: number of gpios to reserve
 * Context: platform init, potentially before irqs or kmalloc will work
 *
 * Returns a negative errno if any gpio within the range is already reserved
 * or registered, else returns zero as a success code.  Use this function
 * to mark a range of gpios as unavailable for dynamic gpio number allocation,
 * for example because its driver support is not yet loaded.
 */
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 work_struct      *work = priv;

        schedule_work(work);
        return IRQ_HANDLED;
}

static void gpio_notify_sysfs(struct work_struct *work)
{
        struct poll_desc        *pdesc;

        pdesc = container_of(work, struct poll_desc, work);
        sysfs_notify_dirent(pdesc->value_sd);
}

static int gpio_setup_irq(struct gpio_desc *desc, struct device *dev,
                unsigned long gpio_flags)
{
        struct poll_desc        *pdesc;
        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 >> PDESC_ID_SHIFT;
        pdesc = idr_find(&pdesc_idr, id);
        if (pdesc) {
                free_irq(irq, &pdesc->work);
                cancel_work_sync(&pdesc->work);
        }

        desc->flags &= ~GPIO_TRIGGER_MASK;

        if (!gpio_flags) {
                ret = 0;
                goto free_sd;
        }

        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 (!pdesc) {
                pdesc = kmalloc(sizeof(*pdesc), GFP_KERNEL);
                if (!pdesc) {
                        ret = -ENOMEM;
                        goto err_out;
                }

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

                if (ret)
                        goto free_mem;

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

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

                pdesc->value_sd = sysfs_get_dirent(dev->kobj.sd, "value");
                if (!pdesc->value_sd) {
                        ret = -ENODEV;
                        goto free_id;
                }
                INIT_WORK(&pdesc->work, gpio_notify_sysfs);
        }

        ret = request_irq(irq, gpio_sysfs_irq, irq_flags,
                        "gpiolib", &pdesc->work);
        if (ret)
                goto free_sd;

        desc->flags |= gpio_flags;
        return 0;

free_sd:
        sysfs_put(pdesc->value_sd);
free_id:
        idr_remove(&pdesc_idr, id);
        desc->flags &= GPIO_FLAGS_MASK;
free_mem:
        kfree(pdesc);
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)
                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,
};


/**
 * gpio_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 gpio_export(unsigned gpio, bool direction_may_change)
{
        unsigned long           flags;
        struct gpio_desc        *desc;
        int                     status = -EINVAL;
        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%d", 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;
}

/**
 * gpio_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 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);


/**
 * gpio_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 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);

/**
 * gpio_unexport - reverse effect of gpio_export()
 * @gpio: gpio to make unavailable
 *
 * This is implicit on gpio_free().
 */
void gpio_unexport(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   *dev = NULL;

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

        mutex_unlock(&sysfs_lock);
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;

        idr_init(&pdesc_idr);

        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 */

/**
 * gpiochip_add() - register a gpio_chip
 * @chip: the chip to register, with chip->base initialized
 * Context: potentially before irqs or kmalloc will work
 *
 * Returns a negative errno if the chip can't be registered, such as
 * because the chip->base is invalid or already associated with a
 * different chip.  Otherwise it returns zero as a success code.
 *
 * When gpiochip_add() is called very early during boot, so that GPIOs
 * can be freely used, the chip->dev device must be registered before
 * the gpio framework's arch_initcall().  Otherwise sysfs initialization
 * for GPIOs will fail rudely.
 *
 * If chip->base is negative, this requests dynamic assignment of
 * a range of valid GPIOs.
 */
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;
                }
        }

unlock:
        spin_unlock_irqrestore(&gpio_lock, flags);
        if (status == 0)
                status = gpiochip_export(chip);
fail:
        /* failures here can mean systems won't boot... */
        if (status)
                pr_err("gpiochip_add: gpios %d..%d (%s) not registered\n",
                        chip->base, chip->base + chip->ngpio - 1,
                        chip->label ? : "generic");
        return status;
}
EXPORT_SYMBOL_GPL(gpiochip_add);

/**
 * gpiochip_remove() - unregister a gpio_chip
 * @chip: the chip to unregister
 *
 * A gpio_chip with any GPIOs still requested may not be removed.
 */
int gpiochip_remove(struct gpio_chip *chip)
{
        unsigned long   flags;
        int             status = 0;
        unsigned        id;

        spin_lock_irqsave(&gpio_lock, flags);

        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);


/* 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 = -EINVAL;
        unsigned long           flags;

        spin_lock_irqsave(&gpio_lock, flags);

        if (!gpio_is_valid(gpio))
                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(extra_checks && 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);
        } else
                WARN_ON(extra_checks);

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

/**
 * gpio_request_one - request a single GPIO with initial configuration
 * @gpio:       the GPIO number
 * @flags:      GPIO configuration as specified by GPIOF_*
 * @label:      a literal description string of this GPIO
 */
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_DIR_IN)
                err = gpio_direction_input(gpio);
        else
                err = gpio_direction_output(gpio,
                                (flags & GPIOF_INIT_HIGH) ? 1 : 0);

        return err;
}
EXPORT_SYMBOL_GPL(gpio_request_one);

/**
 * gpio_request_array - request multiple GPIOs in a single call
 * @array:      array of the 'struct gpio'
 * @num:        how many GPIOs in the array
 */
int gpio_request_array(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);

/**
 * gpio_free_array - release multiple GPIOs in a single call
 * @array:      array of the 'struct gpio'
 * @num:        how many GPIOs in the array
 */
void gpio_free_array(struct gpio *array, size_t num)
{
        while (num--)
                gpio_free((array++)->gpio);
}
EXPORT_SYMBOL_GPL(gpio_free_array);

/**
 * gpiochip_is_requested - return string iff signal was requested
 * @chip: controller managing the signal
 * @offset: of signal within controller's 0..(ngpio - 1) range
 *
 * Returns NULL if the GPIO is not currently requested, else a string.
 * If debugfs support is enabled, the string returned is the label passed
 * to gpio_request(); otherwise it is a meaningless constant.
 *
 * This function is for use by GPIO controller drivers.  The label can
 * help with diagnostics, and knowing that the signal is used as a GPIO
 * can help avoid accidentally multiplexing it to another controller.
 */
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(extra_checks && 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);
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;

        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(extra_checks && 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);
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);


/* 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.
 */

/**
 * __gpio_get_value() - return a gpio's value
 * @gpio: gpio whose value will be returned
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_get_value().
 * It returns the zero or nonzero value provided by the associated
 * gpio_chip.get() method; or zero if no such method is provided.
 */
int __gpio_get_value(unsigned gpio)
{
        struct gpio_chip        *chip;

        chip = gpio_to_chip(gpio);
        WARN_ON(extra_checks && chip->can_sleep);
        return chip->get ? chip->get(chip, gpio - chip->base) : 0;
}
EXPORT_SYMBOL_GPL(__gpio_get_value);

/**
 * __gpio_set_value() - assign a gpio's value
 * @gpio: gpio whose value will be assigned
 * @value: value to assign
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_set_value().
 * It invokes the associated gpio_chip.set() method.
 */
void __gpio_set_value(unsigned gpio, int value)
{
        struct gpio_chip        *chip;

        chip = gpio_to_chip(gpio);
        WARN_ON(extra_checks && chip->can_sleep);
        chip->set(chip, gpio - chip->base, value);
}
EXPORT_SYMBOL_GPL(__gpio_set_value);

/**
 * __gpio_cansleep() - report whether gpio value access will sleep
 * @gpio: gpio in question
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_cansleep().  It
 * returns nonzero if access reading or writing the GPIO value can sleep.
 */
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);

/**
 * __gpio_to_irq() - return the IRQ corresponding to a GPIO
 * @gpio: gpio whose IRQ will be returned (already requested)
 * Context: any
 *
 * This is used directly or indirectly to implement gpio_to_irq().
 * It returns the number of the IRQ signaled by this (input) GPIO,
 * or a negative errno.
 */
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;

        might_sleep_if(extra_checks);
        chip = gpio_to_chip(gpio);
        return chip->get ? chip->get(chip, gpio - chip->base) : 0;
}
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);
        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")
                                : "?  ");

                if (!is_out) {
                        int             irq = gpio_to_irq(gpio);
                        struct irq_desc *desc = irq_to_desc(irq);

                        /* This races with request_irq(), set_irq_type(),
                         * and set_irq_wake() ... but those are "rare".
                         *
                         * More significantly, trigger type flags aren't
                         * currently maintained by genirq.
                         */
                        if (irq >= 0 && desc->action) {
                                char *trigger;

                                switch (desc->status & IRQ_TYPE_SENSE_MASK) {
                                case IRQ_TYPE_NONE:
                                        trigger = "(default)";
                                        break;
                                case IRQ_TYPE_EDGE_FALLING:
                                        trigger = "edge-falling";
                                        break;
                                case IRQ_TYPE_EDGE_RISING:
                                        trigger = "edge-rising";
                                        break;
                                case IRQ_TYPE_EDGE_BOTH:
                                        trigger = "edge-both";
                                        break;
                                case IRQ_TYPE_LEVEL_HIGH:
                                        trigger = "level-high";
                                        break;
                                case IRQ_TYPE_LEVEL_LOW:
                                        trigger = "level-low";
                                        break;
                                default:
                                        trigger = "?trigger?";
                                        break;
                                }

                                seq_printf(s, " irq-%d %s%s",
                                        irq, trigger,
                                        (desc->status & IRQ_WAKEUP)
                                                ? " wakeup" : "");
                        }
                }

                seq_printf(s, "\n");
        }
}

static int gpiolib_show(struct seq_file *s, void *unused)
{
        struct gpio_chip        *chip = NULL;
        unsigned                gpio;
        int                     started = 0;

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

        for (gpio = 0; gpio_is_valid(gpio); gpio++) {
                struct device *dev;

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

                seq_printf(s, "%sGPIOs %d-%d",
                                started ? "\n" : "",
                                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");

                started = 1;
                if (chip->dbg_show)
                        chip->dbg_show(s, chip);
                else
                        gpiolib_dbg_show(s, chip);
        }
        return 0;
}

static int gpiolib_open(struct inode *inode, struct file *file)
{
        return single_open(file, gpiolib_show, NULL);
}

static const struct file_operations gpiolib_operations = {
        .open           = gpiolib_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_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 */