Commit 76abbdde authored by H Hartley Sweeten's avatar H Hartley Sweeten Committed by Thierry Reding
Browse files

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: default avatarH Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Lars Poeschel <poeschel@lemonage.de>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Rob Landley <rob@landley.net>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 3dd0a909

Documentation/ABI/testing/sysfs-class-pwm

0 → 100644
+79 −0
Original line number Diff line number Diff line 
What:		/sys/class/pwm/

Date:		May 2013

KernelVersion:	3.11

Contact:	H Hartley Sweeten <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

Description:

		Unexports a PWM channel.



What:		/sys/class/pwm/pwmchipN/pwmX

Date:		May 2013

KernelVersion:	3.11

Contact:	H Hartley Sweeten <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

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 <hsweeten@visionengravers.com>

Description:

		Enable/disable the PWM signal.

		0 is disabled

		1 is enabled

Documentation/pwm.txt

+37 −0
Original line number Diff line number Diff line
@@ -45,6 +45,43 @@ 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

-----------------------------------



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

+4 −0
Original line number Diff line number Diff line
@@ -28,6 +28,10 @@ menuconfig PWM 


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

+1 −0
Original line number Diff line number Diff line 
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

+23 −2
Original line number Diff line number Diff line
@@ -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_cycle = 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);

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