pwm: Add sysfs interface

Add a simple sysfs interface to the generic PWM framework.

/sys/class/pwm/
`-- pwmchipN/ for each PWM chip
|-- export (w/o) ask the kernel to export a PWM channel
|-- npwm (r/o) number of PWM channels in this PWM chip
|-- pwmX/ for each exported PWM channel
| |-- duty_cycle (r/w) duty cycle (in nanoseconds)
| |-- enable (r/w) enable/disable PWM
| |-- period (r/w) period (in nanoseconds)
| `-- polarity (r/w) polarity of PWM (normal/inversed)
`-- unexport (w/o) return a PWM channel to the kernel

Based on work by Lars Poeschel.

Signed-off-by: H Hartley Sweeten <[e-mail]>
Cc: Thierry Reding <[e-mail]>
Cc: Lars Poeschel <[e-mail]>
Cc: Ryan Mallon <[e-mail]>
Cc: Rob Landley <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

Documentation/ABI/testing/sysfs-class-pwm

···
+What:		/sys/class/pwm/
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		The pwm/ class sub-directory belongs to the Generic PWM
+		Framework and provides a sysfs interface for using PWM
+		channels.
+
+What:		/sys/class/pwm/pwmchipN/
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		A /sys/class/pwm/pwmchipN directory is created for each
+		probed PWM controller/chip where N is the base of the
+		PWM chip.
+
+What:		/sys/class/pwm/pwmchipN/npwm
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		The number of PWM channels supported by the PWM chip.
+
+What:		/sys/class/pwm/pwmchipN/export
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		Exports a PWM channel from the PWM chip for sysfs control.
+		Value is between 0 and /sys/class/pwm/pwmchipN/npwm - 1.
+
+What:		/sys/class/pwm/pwmchipN/unexport
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		Unexports a PWM channel.
+
+What:		/sys/class/pwm/pwmchipN/pwmX
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		A /sys/class/pwm/pwmchipN/pwmX directory is created for
+		each exported PWM channel where X is the exported PWM
+		channel number.
+
+What:		/sys/class/pwm/pwmchipN/pwmX/period
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		Sets the PWM signal period in nanoseconds.
+
+What:		/sys/class/pwm/pwmchipN/pwmX/duty_cycle
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		Sets the PWM signal duty cycle in nanoseconds.
+
+What:		/sys/class/pwm/pwmchipN/pwmX/polarity
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		Sets the output polarity of the PWM signal to "normal" or
+		"inversed".
+
+What:		/sys/class/pwm/pwmchipN/pwmX/enable
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[e-mail]>
+Description:
+		Enable/disable the PWM signal.
+		0 is disabled
+		1 is enabled

Documentation/pwm.txt

···
 
 To start/stop toggling the PWM output use pwm_enable()/pwm_disable().
 
+Using PWMs with the sysfs interface
+-----------------------------------
+
+If CONFIG_SYSFS is enabled in your kernel configuration a simple sysfs
+interface is provided to use the PWMs from userspace. It is exposed at
+/sys/class/pwm/. Each probed PWM controller/chip will be exported as
+pwmchipN, where N is the base of the PWM chip. Inside the directory you
+will find:
+
+npwm - The number of PWM channels this chip supports (read-only).
+
+export - Exports a PWM channel for use with sysfs (write-only).
+
+unexport - Unexports a PWM channel from sysfs (write-only).
+
+The PWM channels are numbered using a per-chip index from 0 to npwm-1.
+
+When a PWM channel is exported a pwmX directory will be created in the
+pwmchipN directory it is associated with, where X is the number of the
+channel that was exported. The following properties will then be available:
+
+period - The total period of the PWM signal (read/write).
+	Value is in nanoseconds and is the sum of the active and inactive
+	time of the PWM.
+
+duty_cycle - The active time of the PWM signal (read/write).
+	Value is in nanoseconds and must be less than the period.
+
+polarity - Changes the polarity of the PWM signal (read/write).
+	Writes to this property only work if the PWM chip supports changing
+	the polarity. The polarity can only be changed if the PWM is not
+	enabled. Value is the string "normal" or "inversed".
+
+enable - Enable/disable the PWM signal (read/write).
+	0 - disabled
+	1 - enabled
+
 Implementing a PWM driver
 -------------------------
 

drivers/pwm/Kconfig

···
 
 if PWM
 
+config PWM_SYSFS
+	bool
+	default y if SYSFS
+
 config PWM_AB8500
 	tristate "AB8500 PWM support"
 	depends on AB8500_CORE && ARCH_U8500

drivers/pwm/Makefile

···
 obj-$(CONFIG_PWM)		+= core.o
+obj-$(CONFIG_PWM_SYSFS)		+= sysfs.o
 obj-$(CONFIG_PWM_AB8500)	+= pwm-ab8500.o
 obj-$(CONFIG_PWM_ATMEL_TCB)	+= pwm-atmel-tcb.o
 obj-$(CONFIG_PWM_BFIN)		+= pwm-bfin.o

drivers/pwm/core.c

···
 	if (IS_ENABLED(CONFIG_OF))
 		of_pwmchip_add(chip);
 
+	pwmchip_sysfs_export(chip);
+
 out:
 	mutex_unlock(&pwm_lock);
 	return ret;
···
 		of_pwmchip_remove(chip);
 
 	free_pwms(chip);
+
+	pwmchip_sysfs_unexport(chip);
 
 out:
 	mutex_unlock(&pwm_lock);
···
  */
 int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
 {
+	int err;
+
 	if (!pwm || duty_ns < 0 || period_ns <= 0 || duty_ns > period_ns)
 		return -EINVAL;
 
-	return pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
+	err = pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
+	if (err)
+		return err;
+
+	pwm->duty_cycle = duty_ns;
+	pwm->period = period_ns;
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(pwm_config);
 
···
  */
 int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
 {
+	int err;
+
 	if (!pwm || !pwm->chip->ops)
 		return -EINVAL;
 
···
 	if (test_bit(PWMF_ENABLED, &pwm->flags))
 		return -EBUSY;
 
-	return pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
+	err = pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
+	if (err)
+		return err;
+
+	pwm->polarity = polarity;
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(pwm_set_polarity);
 

drivers/pwm/sysfs.c

···
+/*
+ * A simple sysfs interface for the generic PWM framework
+ *
+ * Copyright (C) 2013 H Hartley Sweeten <[e-mail]>
+ *
+ * Based on previous work by Lars Poeschel <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#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;
+};
+
+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 pwm_period_show(struct device *child,
+			       struct device_attribute *attr,
+			       char *buf)
+{
+	const struct pwm_device *pwm = child_to_pwm_device(child);
+
+	return sprintf(buf, "%u\n", pwm->period);
+}
+
+static ssize_t pwm_period_store(struct device *child,
+				struct device_attribute *attr,
+				const char *buf, size_t size)
+{
+	struct pwm_device *pwm = child_to_pwm_device(child);
+	unsigned int val;
+	int ret;
+
+	ret = kstrtouint(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	ret = pwm_config(pwm, pwm->duty_cycle, val);
+
+	return ret ? : size;
+}
+
+static ssize_t pwm_duty_cycle_show(struct device *child,
+				   struct device_attribute *attr,
+				   char *buf)
+{
+	const struct pwm_device *pwm = child_to_pwm_device(child);
+
+	return sprintf(buf, "%u\n", pwm->duty_cycle);
+}
+
+static ssize_t pwm_duty_cycle_store(struct device *child,
+				    struct device_attribute *attr,
+				    const char *buf, size_t size)
+{
+	struct pwm_device *pwm = child_to_pwm_device(child);
+	unsigned int val;
+	int ret;
+
+	ret = kstrtouint(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	ret = pwm_config(pwm, val, pwm->period);
+
+	return ret ? : size;
+}
+
+static ssize_t pwm_enable_show(struct device *child,
+			       struct device_attribute *attr,
+			       char *buf)
+{
+	const struct pwm_device *pwm = child_to_pwm_device(child);
+	int enabled = test_bit(PWMF_ENABLED, &pwm->flags);
+
+	return sprintf(buf, "%d\n", enabled);
+}
+
+static ssize_t pwm_enable_store(struct device *child,
+				struct device_attribute *attr,
+				const char *buf, size_t size)
+{
+	struct pwm_device *pwm = child_to_pwm_device(child);
+	int val, ret;
+
+	ret = kstrtoint(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	switch (val) {
+	case 0:
+		pwm_disable(pwm);
+		break;
+	case 1:
+		ret = pwm_enable(pwm);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret ? : size;
+}
+
+static ssize_t pwm_polarity_show(struct device *child,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	const struct pwm_device *pwm = child_to_pwm_device(child);
+
+	return sprintf(buf, "%s\n", pwm->polarity ? "inversed" : "normal");
+}
+
+static ssize_t pwm_polarity_store(struct device *child,
+				  struct device_attribute *attr,
+				  const char *buf, size_t size)
+{
+	struct pwm_device *pwm = child_to_pwm_device(child);
+	enum pwm_polarity polarity;
+	int ret;
+
+	if (sysfs_streq(buf, "normal"))
+		polarity = PWM_POLARITY_NORMAL;
+	else if (sysfs_streq(buf, "inversed"))
+		polarity = PWM_POLARITY_INVERSED;
+	else
+		return -EINVAL;
+
+	ret = pwm_set_polarity(pwm, polarity);
+
+	return ret ? : size;
+}
+
+static DEVICE_ATTR(period, 0644, pwm_period_show, pwm_period_store);
+static DEVICE_ATTR(duty_cycle, 0644, pwm_duty_cycle_show, pwm_duty_cycle_store);
+static DEVICE_ATTR(enable, 0644, pwm_enable_show, pwm_enable_store);
+static DEVICE_ATTR(polarity, 0644, pwm_polarity_show, pwm_polarity_store);
+
+static struct attribute *pwm_attrs[] = {
+	&dev_attr_period.attr,
+	&dev_attr_duty_cycle.attr,
+	&dev_attr_enable.attr,
+	&dev_attr_polarity.attr,
+	NULL
+};
+
+static const struct attribute_group pwm_attr_group = {
+	.attrs		= pwm_attrs,
+};
+
+static const struct attribute_group *pwm_attr_groups[] = {
+	&pwm_attr_group,
+	NULL,
+};
+
+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;
+	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;
+
+	export->child.release = pwm_export_release;
+	export->child.parent = parent;
+	export->child.devt = MKDEV(0, 0);
+	export->child.groups = pwm_attr_groups;
+	dev_set_name(&export->child, "pwm%u", pwm->hwpwm);
+
+	ret = device_register(&export->child);
+	if (ret) {
+		clear_bit(PWMF_EXPORTED, &pwm->flags);
+		kfree(export);
+		return ret;
+	}
+
+	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;
+
+	if (!test_and_clear_bit(PWMF_EXPORTED, &pwm->flags))
+		return -ENODEV;
+
+	child = device_find_child(parent, pwm, pwm_unexport_match);
+	if (!child)
+		return -ENODEV;
+
+	/* for device_find_child() */
+	put_device(child);
+	device_unregister(child);
+	pwm_put(pwm);
+
+	return 0;
+}
+
+static ssize_t pwm_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 ssize_t pwm_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 ssize_t pwm_npwm_show(struct device *parent,
+			     struct device_attribute *attr,
+			     char *buf)
+{
+	const struct pwm_chip *chip = dev_get_drvdata(parent);
+
+	return sprintf(buf, "%u\n", chip->npwm);
+}
+
+static struct device_attribute pwm_chip_attrs[] = {
+	__ATTR(export, 0200, NULL, pwm_export_store),
+	__ATTR(unexport, 0200, NULL, pwm_unexport_store),
+	__ATTR(npwm, 0444, pwm_npwm_show, NULL),
+	__ATTR_NULL,
+};
+
+static struct class pwm_class = {
+	.name		= "pwm",
+	.owner		= THIS_MODULE,
+	.dev_attrs	= pwm_chip_attrs,
+};
+
+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 its 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;
+
+	parent = class_find_device(&pwm_class, NULL, chip,
+				   pwmchip_sysfs_match);
+	if (parent) {
+		/* for class_find_device() */
+		put_device(parent);
+		device_unregister(parent);
+	}
+}
+
+static int __init pwm_sysfs_init(void)
+{
+	return class_register(&pwm_class);
+}
+subsys_initcall(pwm_sysfs_init);

include/linux/pwm.h

···
 enum {
 	PWMF_REQUESTED = 1 << 0,
 	PWMF_ENABLED = 1 << 1,
+	PWMF_EXPORTED = 1 << 2,
 };
 
 struct pwm_device {
···
 	struct pwm_chip		*chip;
 	void			*chip_data;
 
-	unsigned int		period; /* in nanoseconds */
+	unsigned int		period; 	/* in nanoseconds */
+	unsigned int		duty_cycle;	/* in nanoseconds */
+	enum pwm_polarity	polarity;
 };
 
 static inline void pwm_set_period(struct pwm_device *pwm, unsigned int period)
···
 static inline unsigned int pwm_get_period(struct pwm_device *pwm)
 {
 	return pwm ? pwm->period : 0;
+}
+
+static inline void pwm_set_duty_cycle(struct pwm_device *pwm, unsigned int duty)
+{
+	if (pwm)
+		pwm->duty_cycle = duty;
+}
+
+static inline unsigned int pwm_get_duty_cycle(struct pwm_device *pwm)
+{
+	return pwm ? pwm->duty_cycle : 0;
 }
 
 /*
···
 {
 }
 #endif
+
+#ifdef CONFIG_PWM_SYSFS
+void pwmchip_sysfs_export(struct pwm_chip *chip);
+void pwmchip_sysfs_unexport(struct pwm_chip *chip);
+#else
+static inline void pwmchip_sysfs_export(struct pwm_chip *chip)
+{
+}
+
+static inline void pwmchip_sysfs_unexport(struct pwm_chip *chip)
+{
+}
+#endif /* CONFIG_PWM_SYSFS */
 
 #endif /* __LINUX_PWM_H */