drivers/pwm/sysfs.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * A simple sysfs interface for the generic PWM framework
  *
  * Copyright (C) 2013 H Hartley Sweeten <hsweeten@visionengravers.com>
  *
  * Based on previous work by Lars Poeschel <poeschel@lemonage.de>
  */

 #include <linux/device.h>
 #include <linux/mutex.h>
 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/kdev_t.h>
 #include <linux/pwm.h>

 struct pwm_export {
 	struct device child;
 	struct pwm_device *pwm;
 	struct mutex lock;
 	struct pwm_state suspend;
 };

 static struct pwm_export *child_to_pwm_export(struct device *child)
 {
 	return container_of(child, struct pwm_export, child);
 }

 static struct pwm_device *child_to_pwm_device(struct device *child)
 {
 	struct pwm_export *export = child_to_pwm_export(child);

 	return export->pwm;
 }

 static ssize_t period_show(struct device *child,
 			   struct device_attribute *attr,
 			   char *buf)
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
 	struct pwm_state state;

 	pwm_get_state(pwm, &state);

 	return sysfs_emit(buf, "%llu\n", state.period);
 }

 static ssize_t period_store(struct device *child,
 			    struct device_attribute *attr,
 			    const char *buf, size_t size)
 {
 	struct pwm_export *export = child_to_pwm_export(child);
 	struct pwm_device *pwm = export->pwm;
 	struct pwm_state state;
 	u64 val;
 	int ret;

 	ret = kstrtou64(buf, 0, &val);
 	if (ret)
 		return ret;

 	mutex_lock(&export->lock);
 	pwm_get_state(pwm, &state);
 	state.period = val;
 	ret = pwm_apply_state(pwm, &state);
 	mutex_unlock(&export->lock);

 	return ret ? : size;
 }

 static ssize_t duty_cycle_show(struct device *child,
 			       struct device_attribute *attr,
 			       char *buf)
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
 	struct pwm_state state;

 	pwm_get_state(pwm, &state);

 	return sysfs_emit(buf, "%llu\n", state.duty_cycle);
 }

 static ssize_t duty_cycle_store(struct device *child,
 				struct device_attribute *attr,
 				const char *buf, size_t size)
 {
 	struct pwm_export *export = child_to_pwm_export(child);
 	struct pwm_device *pwm = export->pwm;
 	struct pwm_state state;
 	u64 val;
 	int ret;

 	ret = kstrtou64(buf, 0, &val);
 	if (ret)
 		return ret;

 	mutex_lock(&export->lock);
 	pwm_get_state(pwm, &state);
 	state.duty_cycle = val;
 	ret = pwm_apply_state(pwm, &state);
 	mutex_unlock(&export->lock);

 	return ret ? : size;
 }

 static ssize_t enable_show(struct device *child,
 			   struct device_attribute *attr,
 			   char *buf)
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
 	struct pwm_state state;

 	pwm_get_state(pwm, &state);

 	return sysfs_emit(buf, "%d\n", state.enabled);
 }

 static ssize_t enable_store(struct device *child,
 			    struct device_attribute *attr,
 			    const char *buf, size_t size)
 {
 	struct pwm_export *export = child_to_pwm_export(child);
 	struct pwm_device *pwm = export->pwm;
 	struct pwm_state state;
 	int val, ret;

 	ret = kstrtoint(buf, 0, &val);
 	if (ret)
 		return ret;

 	mutex_lock(&export->lock);

 	pwm_get_state(pwm, &state);

 	switch (val) {
 	case 0:
 		state.enabled = false;
 		break;
 	case 1:
 		state.enabled = true;
 		break;
 	default:
 		ret = -EINVAL;
 		goto unlock;
 	}

 	ret = pwm_apply_state(pwm, &state);

 unlock:
 	mutex_unlock(&export->lock);
 	return ret ? : size;
 }

 static ssize_t polarity_show(struct device *child,
 			     struct device_attribute *attr,
 			     char *buf)
 {
 	const struct pwm_device *pwm = child_to_pwm_device(child);
 	const char *polarity = "unknown";
 	struct pwm_state state;

 	pwm_get_state(pwm, &state);

 	switch (state.polarity) {
 	case PWM_POLARITY_NORMAL:
 		polarity = "normal";
 		break;

 	case PWM_POLARITY_INVERSED:
 		polarity = "inversed";
 		break;
 	}

 	return sysfs_emit(buf, "%s\n", polarity);
 }

 static ssize_t polarity_store(struct device *child,
 			      struct device_attribute *attr,
 			      const char *buf, size_t size)
 {
 	struct pwm_export *export = child_to_pwm_export(child);
 	struct pwm_device *pwm = export->pwm;
 	enum pwm_polarity polarity;
 	struct pwm_state state;
 	int ret;

 	if (sysfs_streq(buf, "normal"))
 		polarity = PWM_POLARITY_NORMAL;
 	else if (sysfs_streq(buf, "inversed"))
 		polarity = PWM_POLARITY_INVERSED;
 	else
 		return -EINVAL;

 	mutex_lock(&export->lock);
 	pwm_get_state(pwm, &state);
 	state.polarity = polarity;
 	ret = pwm_apply_state(pwm, &state);
 	mutex_unlock(&export->lock);

 	return ret ? : size;
 }

 static ssize_t capture_show(struct device *child,
 			    struct device_attribute *attr,
 			    char *buf)
 {
 	struct pwm_device *pwm = child_to_pwm_device(child);
 	struct pwm_capture result;
 	int ret;

 	ret = pwm_capture(pwm, &result, jiffies_to_msecs(HZ));
 	if (ret)
 		return ret;

 	return sysfs_emit(buf, "%u %u\n", result.period, result.duty_cycle);
 }

 static DEVICE_ATTR_RW(period);
 static DEVICE_ATTR_RW(duty_cycle);
 static DEVICE_ATTR_RW(enable);
 static DEVICE_ATTR_RW(polarity);
 static DEVICE_ATTR_RO(capture);

 static struct attribute *pwm_attrs[] = {
 	&dev_attr_period.attr,
 	&dev_attr_duty_cycle.attr,
 	&dev_attr_enable.attr,
 	&dev_attr_polarity.attr,
 	&dev_attr_capture.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(pwm);

 static void pwm_export_release(struct device *child)
 {
 	struct pwm_export *export = child_to_pwm_export(child);

 	kfree(export);
 }

 static int pwm_export_child(struct device *parent, struct pwm_device *pwm)
 {
 	struct pwm_export *export;
 	char *pwm_prop[2];
 	int ret;

 	if (test_and_set_bit(PWMF_EXPORTED, &pwm->flags))
 		return -EBUSY;

 	export = kzalloc(sizeof(*export), GFP_KERNEL);
 	if (!export) {
 		clear_bit(PWMF_EXPORTED, &pwm->flags);
 		return -ENOMEM;
 	}

 	export->pwm = pwm;
 	mutex_init(&export->lock);

 	export->child.release = pwm_export_release;
 	export->child.parent = parent;
 	export->child.devt = MKDEV(0, 0);
 	export->child.groups = pwm_groups;
 	dev_set_name(&export->child, "pwm%u", pwm->hwpwm);

 	ret = device_register(&export->child);
 	if (ret) {
 		clear_bit(PWMF_EXPORTED, &pwm->flags);
 		put_device(&export->child);
 		export = NULL;
 		return ret;
 	}
 	pwm_prop[0] = kasprintf(GFP_KERNEL, "EXPORT=pwm%u", pwm->hwpwm);
 	pwm_prop[1] = NULL;
 	kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop);
 	kfree(pwm_prop[0]);

 	return 0;
 }

 static int pwm_unexport_match(struct device *child, void *data)
 {
 	return child_to_pwm_device(child) == data;
 }

 static int pwm_unexport_child(struct device *parent, struct pwm_device *pwm)
 {
 	struct device *child;
 	char *pwm_prop[2];

 	if (!test_and_clear_bit(PWMF_EXPORTED, &pwm->flags))
 		return -ENODEV;

 	child = device_find_child(parent, pwm, pwm_unexport_match);
 	if (!child)
 		return -ENODEV;

 	pwm_prop[0] = kasprintf(GFP_KERNEL, "UNEXPORT=pwm%u", pwm->hwpwm);
 	pwm_prop[1] = NULL;
 	kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop);
 	kfree(pwm_prop[0]);

 	/* for device_find_child() */
 	put_device(child);
 	device_unregister(child);
 	pwm_put(pwm);

 	return 0;
 }

 static ssize_t export_store(struct device *parent,
 			    struct device_attribute *attr,
 			    const char *buf, size_t len)
 {
 	struct pwm_chip *chip = dev_get_drvdata(parent);
 	struct pwm_device *pwm;
 	unsigned int hwpwm;
 	int ret;

 	ret = kstrtouint(buf, 0, &hwpwm);
 	if (ret < 0)
 		return ret;

 	if (hwpwm >= chip->npwm)
 		return -ENODEV;

 	pwm = pwm_request_from_chip(chip, hwpwm, "sysfs");
 	if (IS_ERR(pwm))
 		return PTR_ERR(pwm);

 	ret = pwm_export_child(parent, pwm);
 	if (ret < 0)
 		pwm_put(pwm);

 	return ret ? : len;
 }
 static DEVICE_ATTR_WO(export);

 static ssize_t unexport_store(struct device *parent,
 			      struct device_attribute *attr,
 			      const char *buf, size_t len)
 {
 	struct pwm_chip *chip = dev_get_drvdata(parent);
 	unsigned int hwpwm;
 	int ret;

 	ret = kstrtouint(buf, 0, &hwpwm);
 	if (ret < 0)
 		return ret;

 	if (hwpwm >= chip->npwm)
 		return -ENODEV;

 	ret = pwm_unexport_child(parent, &chip->pwms[hwpwm]);

 	return ret ? : len;
 }
 static DEVICE_ATTR_WO(unexport);

 static ssize_t npwm_show(struct device *parent, struct device_attribute *attr,
 			 char *buf)
 {
 	const struct pwm_chip *chip = dev_get_drvdata(parent);

 	return sysfs_emit(buf, "%u\n", chip->npwm);
 }
 static DEVICE_ATTR_RO(npwm);

 static struct attribute *pwm_chip_attrs[] = {
 	&dev_attr_export.attr,
 	&dev_attr_unexport.attr,
 	&dev_attr_npwm.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(pwm_chip);

 /* takes export->lock on success */
 static struct pwm_export *pwm_class_get_state(struct device *parent,
 					      struct pwm_device *pwm,
 					      struct pwm_state *state)
 {
 	struct device *child;
 	struct pwm_export *export;

 	if (!test_bit(PWMF_EXPORTED, &pwm->flags))
 		return NULL;

 	child = device_find_child(parent, pwm, pwm_unexport_match);
 	if (!child)
 		return NULL;

 	export = child_to_pwm_export(child);
 	put_device(child);	/* for device_find_child() */

 	mutex_lock(&export->lock);
 	pwm_get_state(pwm, state);

 	return export;
 }

 static int pwm_class_apply_state(struct pwm_export *export,
 				 struct pwm_device *pwm,
 				 struct pwm_state *state)
 {
 	int ret = pwm_apply_state(pwm, state);

 	/* release lock taken in pwm_class_get_state */
 	mutex_unlock(&export->lock);

 	return ret;
 }

 static int pwm_class_resume_npwm(struct device *parent, unsigned int npwm)
 {
 	struct pwm_chip *chip = dev_get_drvdata(parent);
 	unsigned int i;
 	int ret = 0;

 	for (i = 0; i < npwm; i++) {
 		struct pwm_device *pwm = &chip->pwms[i];
 		struct pwm_state state;
 		struct pwm_export *export;

 		export = pwm_class_get_state(parent, pwm, &state);
 		if (!export)
 			continue;

 		/* If pwmchip was not enabled before suspend, do nothing. */
 		if (!export->suspend.enabled) {
 			/* release lock taken in pwm_class_get_state */
 			mutex_unlock(&export->lock);
 			continue;
 		}

 		state.enabled = export->suspend.enabled;
 		ret = pwm_class_apply_state(export, pwm, &state);
 		if (ret < 0)
 			break;
 	}

 	return ret;
 }

 static int pwm_class_suspend(struct device *parent)
 {
 	struct pwm_chip *chip = dev_get_drvdata(parent);
 	unsigned int i;
 	int ret = 0;

 	for (i = 0; i < chip->npwm; i++) {
 		struct pwm_device *pwm = &chip->pwms[i];
 		struct pwm_state state;
 		struct pwm_export *export;

 		export = pwm_class_get_state(parent, pwm, &state);
 		if (!export)
 			continue;

 		/*
 		 * If pwmchip was not enabled before suspend, save
 		 * state for resume time and do nothing else.
 		 */
 		export->suspend = state;
 		if (!state.enabled) {
 			/* release lock taken in pwm_class_get_state */
 			mutex_unlock(&export->lock);
 			continue;
 		}

 		state.enabled = false;
 		ret = pwm_class_apply_state(export, pwm, &state);
 		if (ret < 0) {
 			/*
 			 * roll back the PWM devices that were disabled by
 			 * this suspend function.
 			 */
 			pwm_class_resume_npwm(parent, i);
 			break;
 		}
 	}

 	return ret;
 }

 static int pwm_class_resume(struct device *parent)
 {
 	struct pwm_chip *chip = dev_get_drvdata(parent);

 	return pwm_class_resume_npwm(parent, chip->npwm);
 }

 static DEFINE_SIMPLE_DEV_PM_OPS(pwm_class_pm_ops, pwm_class_suspend, pwm_class_resume);

 static struct class pwm_class = {
 	.name = "pwm",
 	.dev_groups = pwm_chip_groups,
 	.pm = pm_sleep_ptr(&pwm_class_pm_ops),
 };

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

 void pwmchip_sysfs_export(struct pwm_chip *chip)
 {
 	struct device *parent;

 	/*
 	 * If device_create() fails the pwm_chip is still usable by
 	 * the kernel it's just not exported.
 	 */
 	parent = device_create(&pwm_class, chip->dev, MKDEV(0, 0), chip,
 			       "pwmchip%d", chip->base);
 	if (IS_ERR(parent)) {
 		dev_warn(chip->dev,
 			 "device_create failed for pwm_chip sysfs export\n");
 	}
 }

 void pwmchip_sysfs_unexport(struct pwm_chip *chip)
 {
 	struct device *parent;
 	unsigned int i;

 	parent = class_find_device(&pwm_class, NULL, chip,
 				   pwmchip_sysfs_match);
 	if (!parent)
 		return;

 	for (i = 0; i < chip->npwm; i++) {
 		struct pwm_device *pwm = &chip->pwms[i];

 		if (test_bit(PWMF_EXPORTED, &pwm->flags))
 			pwm_unexport_child(parent, pwm);
 	}

 	put_device(parent);
 	device_unregister(parent);
 }

 static int __init pwm_sysfs_init(void)
 {
 	return class_register(&pwm_class);
 }
 subsys_initcall(pwm_sysfs_init);
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* A simple sysfs interface for the generic PWM framework
	*
	* Copyright (C) 2013 H Hartley Sweeten <hsweeten@visionengravers.com>
	*
	* Based on previous work by Lars Poeschel <poeschel@lemonage.de>
	*/

	#include <linux/device.h>
	#include <linux/mutex.h>
	#include <linux/err.h>
	#include <linux/slab.h>
	#include <linux/kdev_t.h>
	#include <linux/pwm.h>

	struct pwm_export {
	struct device child;
	struct pwm_device *pwm;
	struct mutex lock;
	struct pwm_state suspend;
	};

	static struct pwm_export child_to_pwm_export(struct device child)
	{
	return container_of(child, struct pwm_export, child);
	}

	static struct pwm_device child_to_pwm_device(struct device child)
	{
	struct pwm_export *export = child_to_pwm_export(child);

	return export->pwm;
	}

	static ssize_t period_show(struct device *child,
	struct device_attribute *attr,
	char *buf)
	{
	const struct pwm_device *pwm = child_to_pwm_device(child);
	struct pwm_state state;

	pwm_get_state(pwm, &state);

	return sysfs_emit(buf, "%llu\n", state.period);
	}

	static ssize_t period_store(struct device *child,
	struct device_attribute *attr,
	const char *buf, size_t size)
	{
	struct pwm_export *export = child_to_pwm_export(child);
	struct pwm_device *pwm = export->pwm;
	struct pwm_state state;
	u64 val;
	int ret;

	ret = kstrtou64(buf, 0, &val);
	if (ret)
	return ret;

	mutex_lock(&export->lock);
	pwm_get_state(pwm, &state);
	state.period = val;
	ret = pwm_apply_state(pwm, &state);
	mutex_unlock(&export->lock);

	return ret ? : size;
	}

	static ssize_t duty_cycle_show(struct device *child,
	struct device_attribute *attr,
	char *buf)
	{
	const struct pwm_device *pwm = child_to_pwm_device(child);
	struct pwm_state state;

	pwm_get_state(pwm, &state);

	return sysfs_emit(buf, "%llu\n", state.duty_cycle);
	}

	static ssize_t duty_cycle_store(struct device *child,
	struct device_attribute *attr,
	const char *buf, size_t size)
	{
	struct pwm_export *export = child_to_pwm_export(child);
	struct pwm_device *pwm = export->pwm;
	struct pwm_state state;
	u64 val;
	int ret;

	ret = kstrtou64(buf, 0, &val);
	if (ret)
	return ret;

	mutex_lock(&export->lock);
	pwm_get_state(pwm, &state);
	state.duty_cycle = val;
	ret = pwm_apply_state(pwm, &state);
	mutex_unlock(&export->lock);

	return ret ? : size;
	}

	static ssize_t enable_show(struct device *child,
	struct device_attribute *attr,
	char *buf)
	{
	const struct pwm_device *pwm = child_to_pwm_device(child);
	struct pwm_state state;

	pwm_get_state(pwm, &state);

	return sysfs_emit(buf, "%d\n", state.enabled);
	}

	static ssize_t enable_store(struct device *child,
	struct device_attribute *attr,
	const char *buf, size_t size)
	{
	struct pwm_export *export = child_to_pwm_export(child);
	struct pwm_device *pwm = export->pwm;
	struct pwm_state state;
	int val, ret;

	ret = kstrtoint(buf, 0, &val);
	if (ret)
	return ret;

	mutex_lock(&export->lock);

	pwm_get_state(pwm, &state);

	switch (val) {
	case 0:
	state.enabled = false;
	break;
	case 1:
	state.enabled = true;
	break;
	default:
	ret = -EINVAL;
	goto unlock;
	}

	ret = pwm_apply_state(pwm, &state);

	unlock:
	mutex_unlock(&export->lock);
	return ret ? : size;
	}

	static ssize_t polarity_show(struct device *child,
	struct device_attribute *attr,
	char *buf)
	{
	const struct pwm_device *pwm = child_to_pwm_device(child);
	const char *polarity = "unknown";
	struct pwm_state state;

	pwm_get_state(pwm, &state);

	switch (state.polarity) {
	case PWM_POLARITY_NORMAL:
	polarity = "normal";
	break;

	case PWM_POLARITY_INVERSED:
	polarity = "inversed";
	break;
	}

	return sysfs_emit(buf, "%s\n", polarity);
	}

	static ssize_t polarity_store(struct device *child,
	struct device_attribute *attr,
	const char *buf, size_t size)
	{
	struct pwm_export *export = child_to_pwm_export(child);
	struct pwm_device *pwm = export->pwm;
	enum pwm_polarity polarity;
	struct pwm_state state;
	int ret;

	if (sysfs_streq(buf, "normal"))
	polarity = PWM_POLARITY_NORMAL;
	else if (sysfs_streq(buf, "inversed"))
	polarity = PWM_POLARITY_INVERSED;
	else
	return -EINVAL;

	mutex_lock(&export->lock);
	pwm_get_state(pwm, &state);
	state.polarity = polarity;
	ret = pwm_apply_state(pwm, &state);
	mutex_unlock(&export->lock);

	return ret ? : size;
	}

	static ssize_t capture_show(struct device *child,
	struct device_attribute *attr,
	char *buf)
	{
	struct pwm_device *pwm = child_to_pwm_device(child);
	struct pwm_capture result;
	int ret;

	ret = pwm_capture(pwm, &result, jiffies_to_msecs(HZ));
	if (ret)
	return ret;

	return sysfs_emit(buf, "%u %u\n", result.period, result.duty_cycle);
	}

	static DEVICE_ATTR_RW(period);
	static DEVICE_ATTR_RW(duty_cycle);
	static DEVICE_ATTR_RW(enable);
	static DEVICE_ATTR_RW(polarity);
	static DEVICE_ATTR_RO(capture);

	static struct attribute *pwm_attrs[] = {
	&dev_attr_period.attr,
	&dev_attr_duty_cycle.attr,
	&dev_attr_enable.attr,
	&dev_attr_polarity.attr,
	&dev_attr_capture.attr,
	NULL
	};
	ATTRIBUTE_GROUPS(pwm);

	static void pwm_export_release(struct device *child)
	{
	struct pwm_export *export = child_to_pwm_export(child);

	kfree(export);
	}

	static int pwm_export_child(struct device parent, struct pwm_device pwm)
	{
	struct pwm_export *export;
	char *pwm_prop[2];
	int ret;

	if (test_and_set_bit(PWMF_EXPORTED, &pwm->flags))
	return -EBUSY;

	export = kzalloc(sizeof(*export), GFP_KERNEL);
	if (!export) {
	clear_bit(PWMF_EXPORTED, &pwm->flags);
	return -ENOMEM;
	}

	export->pwm = pwm;
	mutex_init(&export->lock);

	export->child.release = pwm_export_release;
	export->child.parent = parent;
	export->child.devt = MKDEV(0, 0);
	export->child.groups = pwm_groups;
	dev_set_name(&export->child, "pwm%u", pwm->hwpwm);

	ret = device_register(&export->child);
	if (ret) {
	clear_bit(PWMF_EXPORTED, &pwm->flags);
	put_device(&export->child);
	export = NULL;
	return ret;
	}
	pwm_prop[0] = kasprintf(GFP_KERNEL, "EXPORT=pwm%u", pwm->hwpwm);
	pwm_prop[1] = NULL;
	kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop);
	kfree(pwm_prop[0]);

	return 0;
	}

	static int pwm_unexport_match(struct device child, void data)
	{
	return child_to_pwm_device(child) == data;
	}

	static int pwm_unexport_child(struct device parent, struct pwm_device pwm)
	{
	struct device *child;
	char *pwm_prop[2];

	if (!test_and_clear_bit(PWMF_EXPORTED, &pwm->flags))
	return -ENODEV;

	child = device_find_child(parent, pwm, pwm_unexport_match);
	if (!child)
	return -ENODEV;

	pwm_prop[0] = kasprintf(GFP_KERNEL, "UNEXPORT=pwm%u", pwm->hwpwm);
	pwm_prop[1] = NULL;
	kobject_uevent_env(&parent->kobj, KOBJ_CHANGE, pwm_prop);
	kfree(pwm_prop[0]);

	/* for device_find_child() */
	put_device(child);
	device_unregister(child);
	pwm_put(pwm);

	return 0;
	}

	static ssize_t export_store(struct device *parent,
	struct device_attribute *attr,
	const char *buf, size_t len)
	{
	struct pwm_chip *chip = dev_get_drvdata(parent);
	struct pwm_device *pwm;
	unsigned int hwpwm;
	int ret;

	ret = kstrtouint(buf, 0, &hwpwm);
	if (ret < 0)
	return ret;

	if (hwpwm >= chip->npwm)
	return -ENODEV;

	pwm = pwm_request_from_chip(chip, hwpwm, "sysfs");
	if (IS_ERR(pwm))
	return PTR_ERR(pwm);

	ret = pwm_export_child(parent, pwm);
	if (ret < 0)
	pwm_put(pwm);

	return ret ? : len;
	}
	static DEVICE_ATTR_WO(export);

	static ssize_t unexport_store(struct device *parent,
	struct device_attribute *attr,
	const char *buf, size_t len)
	{
	struct pwm_chip *chip = dev_get_drvdata(parent);
	unsigned int hwpwm;
	int ret;

	ret = kstrtouint(buf, 0, &hwpwm);
	if (ret < 0)
	return ret;

	if (hwpwm >= chip->npwm)
	return -ENODEV;

	ret = pwm_unexport_child(parent, &chip->pwms[hwpwm]);

	return ret ? : len;
	}
	static DEVICE_ATTR_WO(unexport);

	static ssize_t npwm_show(struct device parent, struct device_attribute attr,
	char *buf)
	{
	const struct pwm_chip *chip = dev_get_drvdata(parent);

	return sysfs_emit(buf, "%u\n", chip->npwm);
	}
	static DEVICE_ATTR_RO(npwm);

	static struct attribute *pwm_chip_attrs[] = {
	&dev_attr_export.attr,
	&dev_attr_unexport.attr,
	&dev_attr_npwm.attr,
	NULL,
	};
	ATTRIBUTE_GROUPS(pwm_chip);

	/* takes export->lock on success */
	static struct pwm_export pwm_class_get_state(struct device parent,
	struct pwm_device *pwm,
	struct pwm_state *state)
	{
	struct device *child;
	struct pwm_export *export;

	if (!test_bit(PWMF_EXPORTED, &pwm->flags))
	return NULL;

	child = device_find_child(parent, pwm, pwm_unexport_match);
	if (!child)
	return NULL;

	export = child_to_pwm_export(child);
	put_device(child); /* for device_find_child() */

	mutex_lock(&export->lock);
	pwm_get_state(pwm, state);

	return export;
	}

	static int pwm_class_apply_state(struct pwm_export *export,
	struct pwm_device *pwm,
	struct pwm_state *state)
	{
	int ret = pwm_apply_state(pwm, state);

	/* release lock taken in pwm_class_get_state */
	mutex_unlock(&export->lock);

	return ret;
	}

	static int pwm_class_resume_npwm(struct device *parent, unsigned int npwm)
	{
	struct pwm_chip *chip = dev_get_drvdata(parent);
	unsigned int i;
	int ret = 0;

	for (i = 0; i < npwm; i++) {
	struct pwm_device *pwm = &chip->pwms[i];
	struct pwm_state state;
	struct pwm_export *export;

	export = pwm_class_get_state(parent, pwm, &state);
	if (!export)
	continue;

	/* If pwmchip was not enabled before suspend, do nothing. */
	if (!export->suspend.enabled) {
	/* release lock taken in pwm_class_get_state */
	mutex_unlock(&export->lock);
	continue;
	}

	state.enabled = export->suspend.enabled;
	ret = pwm_class_apply_state(export, pwm, &state);
	if (ret < 0)
	break;
	}

	return ret;
	}

	static int pwm_class_suspend(struct device *parent)
	{
	struct pwm_chip *chip = dev_get_drvdata(parent);
	unsigned int i;
	int ret = 0;

	for (i = 0; i < chip->npwm; i++) {
	struct pwm_device *pwm = &chip->pwms[i];
	struct pwm_state state;
	struct pwm_export *export;

	export = pwm_class_get_state(parent, pwm, &state);
	if (!export)
	continue;

	/*
	* If pwmchip was not enabled before suspend, save
	* state for resume time and do nothing else.
	*/
	export->suspend = state;
	if (!state.enabled) {
	/* release lock taken in pwm_class_get_state */
	mutex_unlock(&export->lock);
	continue;
	}

	state.enabled = false;
	ret = pwm_class_apply_state(export, pwm, &state);
	if (ret < 0) {
	/*
	* roll back the PWM devices that were disabled by
	* this suspend function.
	*/
	pwm_class_resume_npwm(parent, i);
	break;
	}
	}

	return ret;
	}

	static int pwm_class_resume(struct device *parent)
	{
	struct pwm_chip *chip = dev_get_drvdata(parent);

	return pwm_class_resume_npwm(parent, chip->npwm);
	}

	static DEFINE_SIMPLE_DEV_PM_OPS(pwm_class_pm_ops, pwm_class_suspend, pwm_class_resume);

	static struct class pwm_class = {
	.name = "pwm",
	.dev_groups = pwm_chip_groups,
	.pm = pm_sleep_ptr(&pwm_class_pm_ops),
	};

	static int pwmchip_sysfs_match(struct device parent, const void data)
	{
	return dev_get_drvdata(parent) == data;
	}

	void pwmchip_sysfs_export(struct pwm_chip *chip)
	{
	struct device *parent;

	/*
	* If device_create() fails the pwm_chip is still usable by
	* the kernel it's just not exported.
	*/
	parent = device_create(&pwm_class, chip->dev, MKDEV(0, 0), chip,
	"pwmchip%d", chip->base);
	if (IS_ERR(parent)) {
	dev_warn(chip->dev,
	"device_create failed for pwm_chip sysfs export\n");
	}
	}

	void pwmchip_sysfs_unexport(struct pwm_chip *chip)
	{
	struct device *parent;
	unsigned int i;

	parent = class_find_device(&pwm_class, NULL, chip,
	pwmchip_sysfs_match);
	if (!parent)
	return;

	for (i = 0; i < chip->npwm; i++) {
	struct pwm_device *pwm = &chip->pwms[i];

	if (test_bit(PWMF_EXPORTED, &pwm->flags))
	pwm_unexport_child(parent, pwm);
	}

	put_device(parent);
	device_unregister(parent);
	}

	static int __init pwm_sysfs_init(void)
	{
	return class_register(&pwm_class);
	}
	subsys_initcall(pwm_sysfs_init);