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 <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: Thierry Reding <thierry.reding@gmail.com>

Documentation/ABI/testing/sysfs-class-pwm

@@ -0,0 +1,79 @@
+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

@@ -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

@@ -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

@@ -1,4 +1,5 @@
 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

@@ -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);