pwm: add sysfs interface

PATCH Superseded H Hartley Sweeten 1 participant 2 messages May 30, 2013

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H Hartley Sweeten

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2013-05-30 19:30 UTC #0 lore raw

PATCH v2 1/1 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
      |-- npwn           (r/o) number of PWM channels in this PWM chip
      |-- pwmX/          for each exported PWM channel (per PWM chip)
      |   |-- duty_ns    (r/w) duty cycle (in nanoseconds)
      |   |-- enable     (r/w) enable/disable PWM
      |   |-- period_ns  (r/w) period (in nanoseconds)
      |   `-- polarity   (r/w) polarity of PWM
      `-- unexport       (w/o) return a PWM channel to the kernel

Signed-off-by H Hartley Sweeten <[email protected]>

Cc Thierry Reding <[email protected]>

Cc Lars Poeschel <[email protected]>

Cc Ryan Mallon <[email protected]>

Cc Rob Landley <[email protected]>

---
v2: * add API documentation and update Documentation/pwm.txt
* fix some issues pointed out by Ryan Mallon
* add the pwm attributes to dev.groups so they are created when the device is registered for the exported PWM.

 Documentation/ABI/testing/sysfs-class-pwm |  80 +++++++
 Documentation/pwm.txt                     |  39 ++++
 drivers/pwm/Kconfig                       |  12 +
 drivers/pwm/Makefile                      |   1 +
 drivers/pwm/core.c                        |  25 ++-
 drivers/pwm/pwm-sysfs.c                   | 350 ++++++++++++++++++++++++++++++
 include/linux/pwm.h                       |  28 +++
 7 files changed, 533 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-pwm
 create mode 100644 drivers/pwm/pwm-sysfs.c

Documentation/ABI/testing/sysfs-class-pwm new file +80 -0

new file mode 100644
index 0000000..eaa4e1f
@@ -0,0 +1,80 @@
+What:		/sys/class/pwm/
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[email protected]>
+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 <[email protected]>
+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 <[email protected]>
+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 <[email protected]>
+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 <[email protected]>
+Description:
+		Unexports a PWM channel.
+
+What:		/sys/class/pwm/pwmchipN/pwmX
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[email protected]>
+Description:
+		A /sys/class/pwm/pwmchipN/pwmX directory is created for
+		each exported PWM channel where X is the PWM channel number.
+
+What:		/sys/class/pwm/pwmchipN/pwmX/period_ns
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[email protected]>
+Description:
+		Sets the PWM period in nanoseconds.
+
+What:		/sys/class/pwm/pwmchipN/pwmX/duty_ns
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[email protected]>
+Description:
+		Sets the PWM duty cycle in nanoseconds, default is half the
+		/sys/class/pwm/pwmchipN/pwmX/period_ns.
+
+What:		/sys/class/pwm/pwmchipN/pwmX/polarity
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[email protected]>
+Description:
+		Sets the output polarity of the PWM.
+		0 is normal polarity
+		1 is inversed polarity
+
+What:		/sys/class/pwm/pwmchipN/pwmX/enable
+Date:		May 2013
+KernelVersion:	3.11
+Contact:	H Hartley Sweeten <[email protected]>
+Description:
+		Enables/disables the PWM.
+		0 is disabled
+		1 is enabled

Documentation/pwm.txt +39 -0

index 7d2b4c9..b58526d 100644
@@ -45,6 +45,45 @@ int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
 
 To start/stop toggling the PWM output use pwm_enable()/pwm_disable().
 
+Using PWMs with the sysfs interface
+-----------------------------------
+
+You have to enable CONFIG_PWM_SYSFS in your kernel configuration to use
+the sysfs interface. 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 PWM chip specific from 0 to npwn-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 channel number
+that was exported. The following properties will then be available:
+
+period_ns - The total period of the PWM (read/write).
+	Value is in nanoseconds and is the sum of the active and inactive
+	time of the PWM. If duty_ns is zero when this property is written
+	it will be automatically set to half the period_ns.
+
+duty_ns - The active time of the PWM (read/write).
+	Value is in nanoseconds and must be less than the period_ns.
+
+polarity - Changes the polarity of the PWM (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.
+	0 - normal polarity
+	1 - inversed polarity
+
+enable - Enables/disables the PWM (read/write).
+	0 - disabled
+	1 - enabled
+
 Implementing a PWM driver
 -------------------------

drivers/pwm/Kconfig +12 -0

index 115b644..e77405d 100644
@@ -28,6 +28,18 @@ menuconfig PWM
 
 if PWM
 
+config PWM_SYSFS
+	bool "/sys/class/pwm/... (sysfs interface)"
+	depends on SYSFS
+	help
+	  Say Y here to provide a sysfs interface to control PWMs.
+
+	  For every instance of a PWM device there is a pwmchipN directory
+	  created in /sys/class/pwm. Use the export attribute to request
+	  a PWM to be accessible from userspace and the unexport attribute
+	  to return the PWM to the kernel. Each exported PWM will have a
+	  pwmX directory in the pwmchipN it is associated with.
+
 config PWM_AB8500
 	tristate "AB8500 PWM support"
 	depends on AB8500_CORE && ARCH_U8500

drivers/pwm/Makefile +1 -0

index 94ba21e..fb92e1d 100644
@@ -1,4 +1,5 @@
 obj-$(CONFIG_PWM)		+= core.o
+obj-$(CONFIG_PWM_SYSFS)		+= pwm-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 +23 -2

index 32221cb..f67465c 100644
@@ -274,6 +274,8 @@ int pwmchip_add(struct pwm_chip *chip)
 	if (IS_ENABLED(CONFIG_OF))
 		of_pwmchip_add(chip);
 
+	pwmchip_sysfs_export(chip);
+
 out:
 	mutex_unlock(&pwm_lock);
 	return ret;

@@ -310,6 +312,8 @@ int pwmchip_remove(struct pwm_chip *chip)
 
 	free_pwms(chip);
 
+	pwmchip_sysfs_unexport(chip);
+
 out:
 	mutex_unlock(&pwm_lock);
 	return ret;

@@ -402,10 +406,19 @@ EXPORT_SYMBOL_GPL(pwm_free);
  */
 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 = duty_ns;
+	pwm->period = period_ns;
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(pwm_config);

@@ -418,6 +431,8 @@ 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;

@@ -427,7 +442,13 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
 	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/pwm-sysfs.c new file +350 -0

350 lines not on this page · raw message

include/linux/pwm.h +28 -0

index a4df204..6a43484 100644
@@ -76,6 +76,7 @@ enum pwm_polarity {
 enum {
 	PWMF_REQUESTED = 1 << 0,
 	PWMF_ENABLED = 1 << 1,
+	PWMF_EXPORTED = 1 << 2,
 };
 
 struct pwm_device {

@@ -86,7 +87,10 @@ struct pwm_device {
 	struct pwm_chip		*chip;
 	void			*chip_data;
 
+	struct device		*dev;	/* for sysfs export */
 	unsigned int		period; /* in nanoseconds */
+	unsigned int		duty;	/* in nanoseconds */
+	enum pwm_polarity	polarity;
 };
 
 static inline void pwm_set_period(struct pwm_device *pwm, unsigned int period)

@@ -100,6 +104,17 @@ 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 = duty;
+}
+
+static inline unsigned int pwm_get_duty_cycle(struct pwm_device *pwm)
+{
+	return pwm ? pwm->duty : 0;
+}
+
 /*
  * pwm_set_polarity - configure the polarity of a PWM signal
  */

@@ -278,4 +293,17 @@ static inline void pwm_add_table(struct pwm_lookup *table, size_t num)
 }
 #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 */

Signature · 1 line

1.8.1.4

H Hartley Sweeten

author

2013-05-30 21:20 UTC #1 lore raw

Quoted 34 lines · H Hartley Sweeten

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
      |-- npwn           (r/o) number of PWM channels in this PWM chip
      |-- pwmX/          for each exported PWM channel (per PWM chip)
      |   |-- duty_ns    (r/w) duty cycle (in nanoseconds)
      |   |-- enable     (r/w) enable/disable PWM
      |   |-- period_ns  (r/w) period (in nanoseconds)
      |   `-- polarity   (r/w) polarity of PWM
      `-- unexport       (w/o) return a PWM channel to the kernel
Signed-off-by H Hartley Sweeten <[email protected]>
Cc Thierry Reding <[email protected]>
Cc Lars Poeschel <[email protected]>
Cc Ryan Mallon <[email protected]>
Cc Rob Landley <[email protected]>
---
v2: * add API documentation and update Documentation/pwm.txt
* fix some issues pointed out by Ryan Mallon
* add the pwm attributes to dev.groups so they are created when the device is registered for the exported PWM.
 Documentation/ABI/testing/sysfs-class-pwm |  80 +++++++
 Documentation/pwm.txt                     |  39 ++++
 drivers/pwm/Kconfig                       |  12 +
 drivers/pwm/Makefile                      |   1 +
 drivers/pwm/core.c                        |  25 ++-
 drivers/pwm/pwm-sysfs.c                   | 350 ++++++++++++++++++++++++++++++
 include/linux/pwm.h                       |  28 +++
 7 files changed, 533 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-pwm
 create mode 100644 drivers/pwm/pwm-sysfs.c

<snip>

Quoted 1 line

drivers/pwm/pwm-sysfs.c +0 -0

<snip>

drivers/pwm/pwm-sysfs.c line 336

Quoted 9 lines

drivers/pwm/pwm-sysfs.c +9 -0

+void pwmchip_sysfs_export(struct pwm_chip *chip)
+{
+	/*
+	 * If device_create() fails the pwm_chip is still usable by
+	 * the kernel its just not exported.
+	 */
+	chip->dev = device_create(&pwm_class, chip->dev, MKDEV(0, 0), chip,
+				  "pwmchip%d", chip->base);
+}

I just realized this will not work.

chip->dev is initialized by the PWM driver before calling pwmchip_add().

I'll post a v3 shortly.

Regards,
Hartley