Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 854 insertions, 0 deletions

diff --git a/drivers/gpio/gpiolib-sysfs.c b/drivers/gpio/gpiolib-sysfs.c
new file mode 100644
index 000000000..e0ccc79b2
--- /dev/null
+++ b/drivers/gpio/gpiolib-sysfs.c
@@ -0,0 +1,854 @@
+#include <linux/idr.h>
+#include <linux/mutex.h>
+#include <linux/device.h>
+#include <linux/sysfs.h>
+#include <linux/gpio.h>
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/interrupt.h>
+#include <linux/kdev_t.h>
+#include <linux/slab.h>
+#include <linux/ctype.h>
+
+#include "gpiolib.h"
+
+#define GPIO_IRQF_TRIGGER_FALLING	BIT(0)
+#define GPIO_IRQF_TRIGGER_RISING	BIT(1)
+#define GPIO_IRQF_TRIGGER_BOTH		(GPIO_IRQF_TRIGGER_FALLING | \
+					 GPIO_IRQF_TRIGGER_RISING)
+
+struct gpiod_data {
+	struct gpio_desc *desc;
+
+	struct mutex mutex;
+	struct kernfs_node *value_kn;
+	int irq;
+	unsigned char irq_flags;
+
+	bool direction_can_change;
+};
+
+/*
+ * Lock to serialise gpiod export and unexport, and prevent re-export of
+ * gpiod whose chip is being unregistered.
+ */
+static DEFINE_MUTEX(sysfs_lock);
+
+/*
+ * /sys/class/gpio/gpioN... only for GPIOs that are exported
+ *   /direction
+ *      * MAY BE OMITTED if kernel won't allow direction changes
+ *      * is read/write as "in" or "out"
+ *      * may also be written as "high" or "low", initializing
+ *        output value as specified ("out" implies "low")
+ *   /value
+ *      * always readable, subject to hardware behavior
+ *      * may be writable, as zero/nonzero
+ *   /edge
+ *      * configures behavior of poll(2) on /value
+ *      * available only if pin can generate IRQs on input
+ *      * is read/write as "none", "falling", "rising", or "both"
+ *   /active_low
+ *      * configures polarity of /value
+ *      * is read/write as zero/nonzero
+ *      * also affects existing and subsequent "falling" and "rising"
+ *        /edge configuration
+ */
+
+static ssize_t direction_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	struct gpio_desc *desc = data->desc;
+	ssize_t			status;
+
+	mutex_lock(&data->mutex);
+
+	gpiod_get_direction(desc);
+	status = sprintf(buf, "%s\n",
+			test_bit(FLAG_IS_OUT, &desc->flags)
+				? "out" : "in");
+
+	mutex_unlock(&data->mutex);
+
+	return status;
+}
+
+static ssize_t direction_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t size)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	struct gpio_desc *desc = data->desc;
+	ssize_t			status;
+
+	mutex_lock(&data->mutex);
+
+	if (sysfs_streq(buf, "high"))
+		status = gpiod_direction_output_raw(desc, 1);
+	else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
+		status = gpiod_direction_output_raw(desc, 0);
+	else if (sysfs_streq(buf, "in"))
+		status = gpiod_direction_input(desc);
+	else
+		status = -EINVAL;
+
+	mutex_unlock(&data->mutex);
+
+	return status ? : size;
+}
+static DEVICE_ATTR_RW(direction);
+
+static ssize_t value_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	struct gpio_desc *desc = data->desc;
+	ssize_t			status;
+
+	mutex_lock(&data->mutex);
+
+	status = gpiod_get_value_cansleep(desc);
+	if (status < 0)
+		goto err;
+
+	buf[0] = '0' + status;
+	buf[1] = '\n';
+	status = 2;
+err:
+	mutex_unlock(&data->mutex);
+
+	return status;
+}
+
+static ssize_t value_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t size)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	struct gpio_desc *desc = data->desc;
+	ssize_t status = 0;
+
+	mutex_lock(&data->mutex);
+
+	if (!test_bit(FLAG_IS_OUT, &desc->flags)) {
+		status = -EPERM;
+	} else {
+		long		value;
+
+		if (size <= 2 && isdigit(buf[0]) &&
+		    (size == 1 || buf[1] == '\n'))
+			value = buf[0] - '0';
+		else
+			status = kstrtol(buf, 0, &value);
+		if (status == 0) {
+			gpiod_set_value_cansleep(desc, value);
+			status = size;
+		}
+	}
+
+	mutex_unlock(&data->mutex);
+
+	return status;
+}
+static DEVICE_ATTR_PREALLOC(value, S_IWUSR | S_IRUGO, value_show, value_store);
+
+static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
+{
+	struct gpiod_data *data = priv;
+
+	sysfs_notify_dirent(data->value_kn);
+
+	return IRQ_HANDLED;
+}
+
+/* Caller holds gpiod-data mutex. */
+static int gpio_sysfs_request_irq(struct device *dev, unsigned char flags)
+{
+	struct gpiod_data	*data = dev_get_drvdata(dev);
+	struct gpio_desc	*desc = data->desc;
+	unsigned long		irq_flags;
+	int			ret;
+
+	data->irq = gpiod_to_irq(desc);
+	if (data->irq < 0)
+		return -EIO;
+
+	data->value_kn = sysfs_get_dirent(dev->kobj.sd, "value");
+	if (!data->value_kn)
+		return -ENODEV;
+
+	irq_flags = IRQF_SHARED;
+	if (flags & GPIO_IRQF_TRIGGER_FALLING)
+		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
+			IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
+	if (flags & GPIO_IRQF_TRIGGER_RISING)
+		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
+			IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;
+
+	/*
+	 * FIXME: This should be done in the irq_request_resources callback
+	 *        when the irq is requested, but a few drivers currently fail
+	 *        to do so.
+	 *
+	 *        Remove this redundant call (along with the corresponding
+	 *        unlock) when those drivers have been fixed.
+	 */
+	ret = gpiochip_lock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));
+	if (ret < 0)
+		goto err_put_kn;
+
+	ret = request_any_context_irq(data->irq, gpio_sysfs_irq, irq_flags,
+				"gpiolib", data);
+	if (ret < 0)
+		goto err_unlock;
+
+	data->irq_flags = flags;
+
+	return 0;
+
+err_unlock:
+	gpiochip_unlock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));
+err_put_kn:
+	sysfs_put(data->value_kn);
+
+	return ret;
+}
+
+/*
+ * Caller holds gpiod-data mutex (unless called after class-device
+ * deregistration).
+ */
+static void gpio_sysfs_free_irq(struct device *dev)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	struct gpio_desc *desc = data->desc;
+
+	data->irq_flags = 0;
+	free_irq(data->irq, data);
+	gpiochip_unlock_as_irq(desc->gdev->chip, gpio_chip_hwgpio(desc));
+	sysfs_put(data->value_kn);
+}
+
+static const struct {
+	const char *name;
+	unsigned char flags;
+} trigger_types[] = {
+	{ "none",    0 },
+	{ "falling", GPIO_IRQF_TRIGGER_FALLING },
+	{ "rising",  GPIO_IRQF_TRIGGER_RISING },
+	{ "both",    GPIO_IRQF_TRIGGER_BOTH },
+};
+
+static ssize_t edge_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	ssize_t	status = 0;
+	int i;
+
+	mutex_lock(&data->mutex);
+
+	for (i = 0; i < ARRAY_SIZE(trigger_types); i++) {
+		if (data->irq_flags == trigger_types[i].flags) {
+			status = sprintf(buf, "%s\n", trigger_types[i].name);
+			break;
+		}
+	}
+
+	mutex_unlock(&data->mutex);
+
+	return status;
+}
+
+static ssize_t edge_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t size)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	unsigned char flags;
+	ssize_t	status = size;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(trigger_types); i++) {
+		if (sysfs_streq(trigger_types[i].name, buf))
+			break;
+	}
+
+	if (i == ARRAY_SIZE(trigger_types))
+		return -EINVAL;
+
+	flags = trigger_types[i].flags;
+
+	mutex_lock(&data->mutex);
+
+	if (flags == data->irq_flags) {
+		status = size;
+		goto out_unlock;
+	}
+
+	if (data->irq_flags)
+		gpio_sysfs_free_irq(dev);
+
+	if (flags) {
+		status = gpio_sysfs_request_irq(dev, flags);
+		if (!status)
+			status = size;
+	}
+
+out_unlock:
+	mutex_unlock(&data->mutex);
+
+	return status;
+}
+static DEVICE_ATTR_RW(edge);
+
+/* Caller holds gpiod-data mutex. */
+static int gpio_sysfs_set_active_low(struct device *dev, int value)
+{
+	struct gpiod_data	*data = dev_get_drvdata(dev);
+	struct gpio_desc	*desc = data->desc;
+	int			status = 0;
+	unsigned int		flags = data->irq_flags;
+
+	if (!!test_bit(FLAG_ACTIVE_LOW, &desc->flags) == !!value)
+		return 0;
+
+	if (value)
+		set_bit(FLAG_ACTIVE_LOW, &desc->flags);
+	else
+		clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
+
+	/* reconfigure poll(2) support if enabled on one edge only */
+	if (flags == GPIO_IRQF_TRIGGER_FALLING ||
+					flags == GPIO_IRQF_TRIGGER_RISING) {
+		gpio_sysfs_free_irq(dev);
+		status = gpio_sysfs_request_irq(dev, flags);
+	}
+
+	return status;
+}
+
+static ssize_t active_low_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	struct gpio_desc *desc = data->desc;
+	ssize_t			status;
+
+	mutex_lock(&data->mutex);
+
+	status = sprintf(buf, "%d\n",
+				!!test_bit(FLAG_ACTIVE_LOW, &desc->flags));
+
+	mutex_unlock(&data->mutex);
+
+	return status;
+}
+
+static ssize_t active_low_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t size)
+{
+	struct gpiod_data	*data = dev_get_drvdata(dev);
+	ssize_t			status;
+	long			value;
+
+	mutex_lock(&data->mutex);
+
+	status = kstrtol(buf, 0, &value);
+	if (status == 0)
+		status = gpio_sysfs_set_active_low(dev, value);
+
+	mutex_unlock(&data->mutex);
+
+	return status ? : size;
+}
+static DEVICE_ATTR_RW(active_low);
+
+static umode_t gpio_is_visible(struct kobject *kobj, struct attribute *attr,
+			       int n)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct gpiod_data *data = dev_get_drvdata(dev);
+	struct gpio_desc *desc = data->desc;
+	umode_t mode = attr->mode;
+	bool show_direction = data->direction_can_change;
+
+	if (attr == &dev_attr_direction.attr) {
+		if (!show_direction)
+			mode = 0;
+	} else if (attr == &dev_attr_edge.attr) {
+		if (gpiod_to_irq(desc) < 0)
+			mode = 0;
+		if (!show_direction && test_bit(FLAG_IS_OUT, &desc->flags))
+			mode = 0;
+	}
+
+	return mode;
+}
+
+static struct attribute *gpio_attrs[] = {
+	&dev_attr_direction.attr,
+	&dev_attr_edge.attr,
+	&dev_attr_value.attr,
+	&dev_attr_active_low.attr,
+	NULL,
+};
+
+static const struct attribute_group gpio_group = {
+	.attrs = gpio_attrs,
+	.is_visible = gpio_is_visible,
+};
+
+static const struct attribute_group *gpio_groups[] = {
+	&gpio_group,
+	NULL
+};
+
+/*
+ * /sys/class/gpio/gpiochipN/
+ *   /base ... matching gpio_chip.base (N)
+ *   /label ... matching gpio_chip.label
+ *   /ngpio ... matching gpio_chip.ngpio
+ */
+
+static ssize_t base_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	const struct gpio_chip	*chip = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%d\n", chip->base);
+}
+static DEVICE_ATTR_RO(base);
+
+static ssize_t label_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	const struct gpio_chip	*chip = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%s\n", chip->label ? : "");
+}
+static DEVICE_ATTR_RO(label);
+
+static ssize_t ngpio_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	const struct gpio_chip	*chip = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%u\n", chip->ngpio);
+}
+static DEVICE_ATTR_RO(ngpio);
+
+static struct attribute *gpiochip_attrs[] = {
+	&dev_attr_base.attr,
+	&dev_attr_label.attr,
+	&dev_attr_ngpio.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(gpiochip);
+
+static struct gpio_desc *gpio_to_valid_desc(int gpio)
+{
+	return gpio_is_valid(gpio) ? gpio_to_desc(gpio) : NULL;
+}
+
+/*
+ * /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;
+	struct gpio_chip	*gc;
+	int			offset;
+
+	status = kstrtol(buf, 0, &gpio);
+	if (status < 0)
+		goto done;
+
+	desc = gpio_to_valid_desc(gpio);
+	/* reject invalid GPIOs */
+	if (!desc) {
+		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
+		return -EINVAL;
+	}
+	gc = desc->gdev->chip;
+	offset = gpio_chip_hwgpio(desc);
+	if (!gpiochip_line_is_valid(gc, offset)) {
+		pr_warn("%s: GPIO %ld masked\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_set_transitory(desc, false);
+	if (!status) {
+		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 CLASS_ATTR_WO(export);
+
+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_valid_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 CLASS_ATTR_WO(unexport);
+
+static struct attribute *gpio_class_attrs[] = {
+	&class_attr_export.attr,
+	&class_attr_unexport.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(gpio_class);
+
+static struct class gpio_class = {
+	.name =		"gpio",
+	.owner =	THIS_MODULE,
+
+	.class_groups = gpio_class_groups,
+};
+
+
+/**
+ * gpiod_export - export a GPIO through sysfs
+ * @desc: GPIO to make available, already requested
+ * @direction_may_change: true if userspace may change GPIO direction
+ * Context: arch_initcall or later
+ *
+ * When drivers want to make a GPIO accessible to userspace after they
+ * have requested it -- perhaps while debugging, or as part of their
+ * public interface -- they may use this routine.  If the GPIO can
+ * change direction (some can't) and the caller allows it, userspace
+ * will see "direction" sysfs attribute which may be used to change
+ * the gpio's direction.  A "value" attribute will always be provided.
+ *
+ * Returns zero on success, else an error.
+ */
+int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
+{
+	struct gpio_chip	*chip;
+	struct gpio_device	*gdev;
+	struct gpiod_data	*data;
+	unsigned long		flags;
+	int			status;
+	const char		*ioname = NULL;
+	struct device		*dev;
+	int			offset;
+
+	/* can't export until sysfs is available ... */
+	if (!gpio_class.p) {
+		pr_debug("%s: called too early!\n", __func__);
+		return -ENOENT;
+	}
+
+	if (!desc) {
+		pr_debug("%s: invalid gpio descriptor\n", __func__);
+		return -EINVAL;
+	}
+
+	gdev = desc->gdev;
+	chip = gdev->chip;
+
+	mutex_lock(&sysfs_lock);
+
+	/* check if chip is being removed */
+	if (!chip || !gdev->mockdev) {
+		status = -ENODEV;
+		goto err_unlock;
+	}
+
+	spin_lock_irqsave(&gpio_lock, flags);
+	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
+	     test_bit(FLAG_EXPORT, &desc->flags)) {
+		spin_unlock_irqrestore(&gpio_lock, flags);
+		gpiod_dbg(desc, "%s: unavailable (requested=%d, exported=%d)\n",
+				__func__,
+				test_bit(FLAG_REQUESTED, &desc->flags),
+				test_bit(FLAG_EXPORT, &desc->flags));
+		status = -EPERM;
+		goto err_unlock;
+	}
+	spin_unlock_irqrestore(&gpio_lock, flags);
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data) {
+		status = -ENOMEM;
+		goto err_unlock;
+	}
+
+	data->desc = desc;
+	mutex_init(&data->mutex);
+	if (chip->direction_input && chip->direction_output)
+		data->direction_can_change = direction_may_change;
+	else
+		data->direction_can_change = false;
+
+	offset = gpio_chip_hwgpio(desc);
+	if (chip->names && chip->names[offset])
+		ioname = chip->names[offset];
+
+	dev = device_create_with_groups(&gpio_class, &gdev->dev,
+					MKDEV(0, 0), data, gpio_groups,
+					ioname ? ioname : "gpio%u",
+					desc_to_gpio(desc));
+	if (IS_ERR(dev)) {
+		status = PTR_ERR(dev);
+		goto err_free_data;
+	}
+
+	set_bit(FLAG_EXPORT, &desc->flags);
+	mutex_unlock(&sysfs_lock);
+	return 0;
+
+err_free_data:
+	kfree(data);
+err_unlock:
+	mutex_unlock(&sysfs_lock);
+	gpiod_dbg(desc, "%s: status %d\n", __func__, status);
+	return status;
+}
+EXPORT_SYMBOL_GPL(gpiod_export);
+
+static int match_export(struct device *dev, const void *desc)
+{
+	struct gpiod_data *data = dev_get_drvdata(dev);
+
+	return data->desc == desc;
+}
+
+/**
+ * gpiod_export_link - create a sysfs link to an exported GPIO node
+ * @dev: device under which to create symlink
+ * @name: name of the symlink
+ * @desc: GPIO to create symlink to, already exported
+ *
+ * Set up a symlink from /sys/.../dev/name to /sys/class/gpio/gpioN
+ * node. Caller is responsible for unlinking.
+ *
+ * Returns zero on success, else an error.
+ */
+int gpiod_export_link(struct device *dev, const char *name,
+		      struct gpio_desc *desc)
+{
+	struct device *cdev;
+	int ret;
+
+	if (!desc) {
+		pr_warn("%s: invalid GPIO\n", __func__);
+		return -EINVAL;
+	}
+
+	cdev = class_find_device(&gpio_class, NULL, desc, match_export);
+	if (!cdev)
+		return -ENODEV;
+
+	ret = sysfs_create_link(&dev->kobj, &cdev->kobj, name);
+	put_device(cdev);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(gpiod_export_link);
+
+/**
+ * gpiod_unexport - reverse effect of gpiod_export()
+ * @desc: GPIO to make unavailable
+ *
+ * This is implicit on gpiod_free().
+ */
+void gpiod_unexport(struct gpio_desc *desc)
+{
+	struct gpiod_data *data;
+	struct device *dev;
+
+	if (!desc) {
+		pr_warn("%s: invalid GPIO\n", __func__);
+		return;
+	}
+
+	mutex_lock(&sysfs_lock);
+
+	if (!test_bit(FLAG_EXPORT, &desc->flags))
+		goto err_unlock;
+
+	dev = class_find_device(&gpio_class, NULL, desc, match_export);
+	if (!dev)
+		goto err_unlock;
+
+	data = dev_get_drvdata(dev);
+
+	clear_bit(FLAG_EXPORT, &desc->flags);
+
+	device_unregister(dev);
+
+	/*
+	 * Release irq after deregistration to prevent race with edge_store.
+	 */
+	if (data->irq_flags)
+		gpio_sysfs_free_irq(dev);
+
+	mutex_unlock(&sysfs_lock);
+
+	put_device(dev);
+	kfree(data);
+
+	return;
+
+err_unlock:
+	mutex_unlock(&sysfs_lock);
+}
+EXPORT_SYMBOL_GPL(gpiod_unexport);
+
+int gpiochip_sysfs_register(struct gpio_device *gdev)
+{
+	struct device	*dev;
+	struct device	*parent;
+	struct gpio_chip *chip = gdev->chip;
+
+	/*
+	 * Many systems add gpio chips for SOC support very early,
+	 * before driver model support is available.  In those cases we
+	 * register later, in gpiolib_sysfs_init() ... here we just
+	 * verify that _some_ field of gpio_class got initialized.
+	 */
+	if (!gpio_class.p)
+		return 0;
+
+	/*
+	 * For sysfs backward compatibility we need to preserve this
+	 * preferred parenting to the gpio_chip parent field, if set.
+	 */
+	if (chip->parent)
+		parent = chip->parent;
+	else
+		parent = &gdev->dev;
+
+	/* use chip->base for the ID; it's already known to be unique */
+	dev = device_create_with_groups(&gpio_class, parent,
+					MKDEV(0, 0),
+					chip, gpiochip_groups,
+					"gpiochip%d", chip->base);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+
+	mutex_lock(&sysfs_lock);
+	gdev->mockdev = dev;
+	mutex_unlock(&sysfs_lock);
+
+	return 0;
+}
+
+void gpiochip_sysfs_unregister(struct gpio_device *gdev)
+{
+	struct gpio_desc *desc;
+	struct gpio_chip *chip = gdev->chip;
+	unsigned int i;
+
+	if (!gdev->mockdev)
+		return;
+
+	device_unregister(gdev->mockdev);
+
+	/* prevent further gpiod exports */
+	mutex_lock(&sysfs_lock);
+	gdev->mockdev = NULL;
+	mutex_unlock(&sysfs_lock);
+
+	/* unregister gpiod class devices owned by sysfs */
+	for (i = 0; i < chip->ngpio; i++) {
+		desc = &gdev->descs[i];
+		if (test_and_clear_bit(FLAG_SYSFS, &desc->flags))
+			gpiod_free(desc);
+	}
+}
+
+static int __init gpiolib_sysfs_init(void)
+{
+	int		status;
+	unsigned long	flags;
+	struct gpio_device *gdev;
+
+	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(gdev, &gpio_devices, list) {
+		if (gdev->mockdev)
+			continue;
+
+		/*
+		 * TODO we yield gpio_lock here because
+		 * gpiochip_sysfs_register() acquires a mutex. This is unsafe
+		 * and needs to be fixed.
+		 *
+		 * Also it would be nice to use gpiochip_find() here so we
+		 * can keep gpio_chips local to gpiolib.c, but the yield of
+		 * gpio_lock prevents us from doing this.
+		 */
+		spin_unlock_irqrestore(&gpio_lock, flags);
+		status = gpiochip_sysfs_register(gdev);
+		spin_lock_irqsave(&gpio_lock, flags);
+	}
+	spin_unlock_irqrestore(&gpio_lock, flags);
+
+	return status;
+}
+postcore_initcall(gpiolib_sysfs_init);