gpio: move sysfs support to its own file

sysfs support is currently entangled within the core GPIO support, while
it should relly just be a (privileged) user of the integer GPIO API.
This patch is a first step towards making the gpiolib code more readable
by splitting it into logical parts.

Move all sysfs support to their own source file, and share static
members of gpiolib that need to be in the private gpiolib.h file. In
the future we will want to put some of them back into gpiolib.c, but this
first patch let us at least identify them.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 829 insertions, 0 deletions

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
new file mode 100644
index 000000000000..3516502059f2
--- /dev/null
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -0,0 +1,829 @@
+#include <linux/idr.h>
+#include <linux/mutex.h>
+#include <linux/device.h>
+#include <linux/sysfs.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/interrupt.h>
+#include <linux/kdev_t.h>
+
+#include "gpiolib.h"
+
+static DEFINE_IDR(dirent_idr);
+
+
+/* lock protects against unexport_gpio() being called while
+ * sysfs files are active.
+ */
+static DEFINE_MUTEX(sysfs_lock);
+
+/*
+ * /sys/class/gpio/gpioN... only for GPIOs that are exported
+ *   /direction
+ *      * MAY BE OMITTED if kernel won't allow direction changes
+ *      * is read/write as "in" or "out"
+ *      * may also be written as "high" or "low", initializing
+ *        output value as specified ("out" implies "low")
+ *   /value
+ *      * always readable, subject to hardware behavior
+ *      * may be writable, as zero/nonzero
+ *   /edge
+ *      * configures behavior of poll(2) on /value
+ *      * available only if pin can generate IRQs on input
+ *      * is read/write as "none", "falling", "rising", or "both"
+ *   /active_low
+ *      * configures polarity of /value
+ *      * is read/write as zero/nonzero
+ *      * also affects existing and subsequent "falling" and "rising"
+ *        /edge configuration
+ */
+
+static ssize_t gpio_direction_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	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 {
+		gpiod_get_direction(desc);
+		status = sprintf(buf, "%s\n",
+			test_bit(FLAG_IS_OUT, &desc->flags)
+				? "out" : "in");
+	}
+
+	mutex_unlock(&sysfs_lock);
+	return status;
+}
+
+static ssize_t gpio_direction_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t size)
+{
+	struct gpio_desc	*desc = dev_get_drvdata(dev);
+	ssize_t			status;
+
+	mutex_lock(&sysfs_lock);
+
+	if (!test_bit(FLAG_EXPORT, &desc->flags))
+		status = -EIO;
+	else if (sysfs_streq(buf, "high"))
+		status = gpiod_direction_output_raw(desc, 1);
+	else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
+		status = gpiod_direction_output_raw(desc, 0);
+	else if (sysfs_streq(buf, "in"))
+		status = gpiod_direction_input(desc);
+	else
+		status = -EINVAL;
+
+	mutex_unlock(&sysfs_lock);
+	return status ? : size;
+}
+
+static /* const */ DEVICE_ATTR(direction, 0644,
+		gpio_direction_show, gpio_direction_store);
+
+static ssize_t gpio_value_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gpio_desc	*desc = dev_get_drvdata(dev);
+	ssize_t			status;
+
+	mutex_lock(&sysfs_lock);
+
+	if (!test_bit(FLAG_EXPORT, &desc->flags))
+		status = -EIO;
+	else
+		status = sprintf(buf, "%d\n", gpiod_get_value_cansleep(desc));
+
+	mutex_unlock(&sysfs_lock);
+	return status;
+}
+
+static ssize_t gpio_value_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t size)
+{
+	struct gpio_desc	*desc = dev_get_drvdata(dev);
+	ssize_t			status;
+
+	mutex_lock(&sysfs_lock);
+
+	if (!test_bit(FLAG_EXPORT, &desc->flags))
+		status = -EIO;
+	else if (!test_bit(FLAG_IS_OUT, &desc->flags))
+		status = -EPERM;
+	else {
+		long		value;
+
+		status = kstrtol(buf, 0, &value);
+		if (status == 0) {
+			gpiod_set_value_cansleep(desc, value);
+			status = size;
+		}
+	}
+
+	mutex_unlock(&sysfs_lock);
+	return status;
+}
+
+static const DEVICE_ATTR(value, 0644,
+		gpio_value_show, gpio_value_store);
+
+static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
+{
+	struct kernfs_node	*value_sd = priv;
+
+	sysfs_notify_dirent(value_sd);
+	return IRQ_HANDLED;
+}
+
+static int gpio_setup_irq(struct gpio_desc *desc, struct device *dev,
+		unsigned long gpio_flags)
+{
+	struct kernfs_node	*value_sd;
+	unsigned long		irq_flags;
+	int			ret, irq, id;
+
+	if ((desc->flags & GPIO_TRIGGER_MASK) == gpio_flags)
+		return 0;
+
+	irq = gpiod_to_irq(desc);
+	if (irq < 0)
+		return -EIO;
+
+	id = desc->flags >> ID_SHIFT;
+	value_sd = idr_find(&dirent_idr, id);
+	if (value_sd)
+		free_irq(irq, value_sd);
+
+	desc->flags &= ~GPIO_TRIGGER_MASK;
+
+	if (!gpio_flags) {
+		gpiod_unlock_as_irq(desc);
+		ret = 0;
+		goto free_id;
+	}
+
+	irq_flags = IRQF_SHARED;
+	if (test_bit(FLAG_TRIG_FALL, &gpio_flags))
+		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
+			IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
+	if (test_bit(FLAG_TRIG_RISE, &gpio_flags))
+		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
+			IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;
+
+	if (!value_sd) {
+		value_sd = sysfs_get_dirent(dev->kobj.sd, "value");
+		if (!value_sd) {
+			ret = -ENODEV;
+			goto err_out;
+		}
+
+		ret = idr_alloc(&dirent_idr, value_sd, 1, 0, GFP_KERNEL);
+		if (ret < 0)
+			goto free_sd;
+		id = ret;
+
+		desc->flags &= GPIO_FLAGS_MASK;
+		desc->flags |= (unsigned long)id << ID_SHIFT;
+
+		if (desc->flags >> ID_SHIFT != id) {
+			ret = -ERANGE;
+			goto free_id;
+		}
+	}
+
+	ret = request_any_context_irq(irq, gpio_sysfs_irq, irq_flags,
+				"gpiolib", value_sd);
+	if (ret < 0)
+		goto free_id;
+
+	ret = gpiod_lock_as_irq(desc);
+	if (ret < 0) {
+		gpiod_warn(desc, "failed to flag the GPIO for IRQ\n");
+		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 = kstrtol(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;
+	struct gpio_desc	*desc;
+	int			status;
+
+	status = kstrtol(buf, 0, &gpio);
+	if (status < 0)
+		goto done;
+
+	desc = gpio_to_desc(gpio);
+	/* reject invalid GPIOs */
+	if (!desc) {
+		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
+		return -EINVAL;
+	}
+
+	/* No extra locking here; FLAG_SYSFS just signifies that the
+	 * request and export were done by on behalf of userspace, so
+	 * they may be undone on its behalf too.
+	 */
+
+	status = gpiod_request(desc, "sysfs");
+	if (status < 0) {
+		if (status == -EPROBE_DEFER)
+			status = -ENODEV;
+		goto done;
+	}
+	status = gpiod_export(desc, true);
+	if (status < 0)
+		gpiod_free(desc);
+	else
+		set_bit(FLAG_SYSFS, &desc->flags);
+
+done:
+	if (status)
+		pr_debug("%s: status %d\n", __func__, status);
+	return status ? : len;
+}
+
+static ssize_t unexport_store(struct class *class,
+				struct class_attribute *attr,
+				const char *buf, size_t len)
+{
+	long			gpio;
+	struct gpio_desc	*desc;
+	int			status;
+
+	status = kstrtol(buf, 0, &gpio);
+	if (status < 0)
+		goto done;
+
+	desc = gpio_to_desc(gpio);
+	/* reject bogus commands (gpio_unexport ignores them) */
+	if (!desc) {
+		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
+		return -EINVAL;
+	}
+
+	status = -EINVAL;
+
+	/* No extra locking here; FLAG_SYSFS just signifies that the
+	 * request and export were done by on behalf of userspace, so
+	 * they may be undone on its behalf too.
+	 */
+	if (test_and_clear_bit(FLAG_SYSFS, &desc->flags)) {
+		status = 0;
+		gpiod_free(desc);
+	}
+done:
+	if (status)
+		pr_debug("%s: status %d\n", __func__, status);
+	return status ? : len;
+}
+
+static struct class_attribute gpio_class_attrs[] = {
+	__ATTR(export, 0200, NULL, export_store),
+	__ATTR(unexport, 0200, NULL, unexport_store),
+	__ATTR_NULL,
+};
+
+static struct class gpio_class = {
+	.name =		"gpio",
+	.owner =	THIS_MODULE,
+
+	.class_attrs =	gpio_class_attrs,
+};
+
+
+/**
+ * gpiod_export - export a GPIO through sysfs
+ * @gpio: gpio to make available, already requested
+ * @direction_may_change: true if userspace may change gpio direction
+ * Context: arch_initcall or later
+ *
+ * When drivers want to make a GPIO accessible to userspace after they
+ * have requested it -- perhaps while debugging, or as part of their
+ * public interface -- they may use this routine.  If the GPIO can
+ * change direction (some can't) and the caller allows it, userspace
+ * will see "direction" sysfs attribute which may be used to change
+ * the gpio's direction.  A "value" attribute will always be provided.
+ *
+ * Returns zero on success, else an error.
+ */
+int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
+{
+	unsigned long		flags;
+	int			status;
+	const char		*ioname = NULL;
+	struct device		*dev;
+	int			offset;
+
+	/* can't export until sysfs is available ... */
+	if (!gpio_class.p) {
+		pr_debug("%s: called too early!\n", __func__);
+		return -ENOENT;
+	}
+
+	if (!desc) {
+		pr_debug("%s: invalid gpio descriptor\n", __func__);
+		return -EINVAL;
+	}
+
+	mutex_lock(&sysfs_lock);
+
+	spin_lock_irqsave(&gpio_lock, flags);
+	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
+	     test_bit(FLAG_EXPORT, &desc->flags)) {
+		spin_unlock_irqrestore(&gpio_lock, flags);
+		gpiod_dbg(desc, "%s: unavailable (requested=%d, exported=%d)\n",
+				__func__,
+				test_bit(FLAG_REQUESTED, &desc->flags),
+				test_bit(FLAG_EXPORT, &desc->flags));
+		status = -EPERM;
+		goto fail_unlock;
+	}
+
+	if (!desc->chip->direction_input || !desc->chip->direction_output)
+		direction_may_change = false;
+	spin_unlock_irqrestore(&gpio_lock, flags);
+
+	offset = gpio_chip_hwgpio(desc);
+	if (desc->chip->names && desc->chip->names[offset])
+		ioname = desc->chip->names[offset];
+
+	dev = device_create(&gpio_class, desc->chip->dev, MKDEV(0, 0),
+			    desc, ioname ? ioname : "gpio%u",
+			    desc_to_gpio(desc));
+	if (IS_ERR(dev)) {
+		status = PTR_ERR(dev);
+		goto fail_unlock;
+	}
+
+	status = sysfs_create_group(&dev->kobj, &gpio_attr_group);
+	if (status)
+		goto fail_unregister_device;
+
+	if (direction_may_change) {
+		status = device_create_file(dev, &dev_attr_direction);
+		if (status)
+			goto fail_unregister_device;
+	}
+
+	if (gpiod_to_irq(desc) >= 0 && (direction_may_change ||
+				       !test_bit(FLAG_IS_OUT, &desc->flags))) {
+		status = device_create_file(dev, &dev_attr_edge);
+		if (status)
+			goto fail_unregister_device;
+	}
+
+	set_bit(FLAG_EXPORT, &desc->flags);
+	mutex_unlock(&sysfs_lock);
+	return 0;
+
+fail_unregister_device:
+	device_unregister(dev);
+fail_unlock:
+	mutex_unlock(&sysfs_lock);
+	gpiod_dbg(desc, "%s: status %d\n", __func__, status);
+	return status;
+}
+EXPORT_SYMBOL_GPL(gpiod_export);
+
+static int match_export(struct device *dev, const void *data)
+{
+	return dev_get_drvdata(dev) == data;
+}
+
+/**
+ * gpiod_export_link - create a sysfs link to an exported GPIO node
+ * @dev: device under which to create symlink
+ * @name: name of the symlink
+ * @gpio: gpio to create symlink to, already exported
+ *
+ * Set up a symlink from /sys/.../dev/name to /sys/class/gpio/gpioN
+ * node. Caller is responsible for unlinking.
+ *
+ * Returns zero on success, else an error.
+ */
+int gpiod_export_link(struct device *dev, const char *name,
+		      struct gpio_desc *desc)
+{
+	int			status = -EINVAL;
+
+	if (!desc) {
+		pr_warn("%s: invalid GPIO\n", __func__);
+		return -EINVAL;
+	}
+
+	mutex_lock(&sysfs_lock);
+
+	if (test_bit(FLAG_EXPORT, &desc->flags)) {
+		struct device *tdev;
+
+		tdev = class_find_device(&gpio_class, NULL, desc, match_export);
+		if (tdev != NULL) {
+			status = sysfs_create_link(&dev->kobj, &tdev->kobj,
+						name);
+		} else {
+			status = -ENODEV;
+		}
+	}
+
+	mutex_unlock(&sysfs_lock);
+
+	if (status)
+		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(gpiod_export_link);
+
+/**
+ * gpiod_sysfs_set_active_low - set the polarity of gpio sysfs value
+ * @gpio: gpio to change
+ * @value: non-zero to use active low, i.e. inverted values
+ *
+ * Set the polarity of /sys/class/gpio/gpioN/value sysfs attribute.
+ * The GPIO does not have to be exported yet.  If poll(2) support has
+ * been enabled for either rising or falling edge, it will be
+ * reconfigured to follow the new polarity.
+ *
+ * Returns zero on success, else an error.
+ */
+int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value)
+{
+	struct device		*dev = NULL;
+	int			status = -EINVAL;
+
+	if (!desc) {
+		pr_warn("%s: invalid GPIO\n", __func__);
+		return -EINVAL;
+	}
+
+	mutex_lock(&sysfs_lock);
+
+	if (test_bit(FLAG_EXPORT, &desc->flags)) {
+		dev = class_find_device(&gpio_class, NULL, desc, match_export);
+		if (dev == NULL) {
+			status = -ENODEV;
+			goto unlock;
+		}
+	}
+
+	status = sysfs_set_active_low(desc, dev, value);
+
+unlock:
+	mutex_unlock(&sysfs_lock);
+
+	if (status)
+		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
+
+	return status;
+}
+EXPORT_SYMBOL_GPL(gpiod_sysfs_set_active_low);
+
+/**
+ * gpiod_unexport - reverse effect of gpio_export()
+ * @gpio: gpio to make unavailable
+ *
+ * This is implicit on gpio_free().
+ */
+void gpiod_unexport(struct gpio_desc *desc)
+{
+	int			status = 0;
+	struct device		*dev = NULL;
+
+	if (!desc) {
+		pr_warn("%s: invalid GPIO\n", __func__);
+		return;
+	}
+
+	mutex_lock(&sysfs_lock);
+
+	if (test_bit(FLAG_EXPORT, &desc->flags)) {
+
+		dev = class_find_device(&gpio_class, NULL, desc, match_export);
+		if (dev) {
+			gpio_setup_irq(desc, dev, 0);
+			clear_bit(FLAG_EXPORT, &desc->flags);
+		} else
+			status = -ENODEV;
+	}
+
+	mutex_unlock(&sysfs_lock);
+
+	if (dev) {
+		device_unregister(dev);
+		put_device(dev);
+	}
+
+	if (status)
+		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
+}
+EXPORT_SYMBOL_GPL(gpiod_unexport);
+
+int gpiochip_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 = 0;
+		while (gpio < chip->ngpio)
+			chip->desc[gpio++].chip = NULL;
+		spin_unlock_irqrestore(&gpio_lock, flags);
+
+		chip_dbg(chip, "%s: status %d\n", __func__, status);
+	}
+
+	return status;
+}
+
+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 = false;
+		status = 0;
+	} else
+		status = -ENODEV;
+	mutex_unlock(&sysfs_lock);
+
+	if (status)
+		chip_dbg(chip, "%s: status %d\n", __func__, status);
+}
+
+static int __init gpiolib_sysfs_init(void)
+{
+	int		status;
+	unsigned long	flags;
+	struct gpio_chip *chip;
+
+	status = class_register(&gpio_class);
+	if (status < 0)
+		return status;
+
+	/* Scan and register the gpio_chips which registered very
+	 * early (e.g. before the class_register above was called).
+	 *
+	 * We run before arch_initcall() so chip->dev nodes can have
+	 * registered, and so arch_initcall() can always gpio_export().
+	 */
+	spin_lock_irqsave(&gpio_lock, flags);
+	list_for_each_entry(chip, &gpio_chips, list) {
+		if (!chip || 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);