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H Hartley Sweetenthierryreding
H Hartley Sweeten
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thierryreding
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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>
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‎Documentation/ABI/testing/sysfs-class-pwm

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,79 @@
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What: /sys/class/pwm/
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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The pwm/ class sub-directory belongs to the Generic PWM
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Framework and provides a sysfs interface for using PWM
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channels.
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What: /sys/class/pwm/pwmchipN/
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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A /sys/class/pwm/pwmchipN directory is created for each
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probed PWM controller/chip where N is the base of the
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PWM chip.
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What: /sys/class/pwm/pwmchipN/npwm
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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The number of PWM channels supported by the PWM chip.
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What: /sys/class/pwm/pwmchipN/export
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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Exports a PWM channel from the PWM chip for sysfs control.
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Value is between 0 and /sys/class/pwm/pwmchipN/npwm - 1.
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What: /sys/class/pwm/pwmchipN/unexport
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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Unexports a PWM channel.
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What: /sys/class/pwm/pwmchipN/pwmX
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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A /sys/class/pwm/pwmchipN/pwmX directory is created for
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each exported PWM channel where X is the exported PWM
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channel number.
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What: /sys/class/pwm/pwmchipN/pwmX/period
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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Sets the PWM signal period in nanoseconds.
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What: /sys/class/pwm/pwmchipN/pwmX/duty_cycle
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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Sets the PWM signal duty cycle in nanoseconds.
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What: /sys/class/pwm/pwmchipN/pwmX/polarity
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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Sets the output polarity of the PWM signal to "normal" or
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"inversed".
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What: /sys/class/pwm/pwmchipN/pwmX/enable
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Date: May 2013
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KernelVersion: 3.11
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Contact: H Hartley Sweeten <hsweeten@visionengravers.com>
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Description:
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Enable/disable the PWM signal.
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0 is disabled
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1 is enabled

‎Documentation/pwm.txt

+37
Original file line numberDiff line numberDiff line change
@@ -45,6 +45,43 @@ int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
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4646
To start/stop toggling the PWM output use pwm_enable()/pwm_disable().
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Using PWMs with the sysfs interface
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-----------------------------------
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If CONFIG_SYSFS is enabled in your kernel configuration a simple sysfs
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interface is provided to use the PWMs from userspace. It is exposed at
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/sys/class/pwm/. Each probed PWM controller/chip will be exported as
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pwmchipN, where N is the base of the PWM chip. Inside the directory you
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will find:
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npwm - The number of PWM channels this chip supports (read-only).
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export - Exports a PWM channel for use with sysfs (write-only).
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unexport - Unexports a PWM channel from sysfs (write-only).
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The PWM channels are numbered using a per-chip index from 0 to npwm-1.
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When a PWM channel is exported a pwmX directory will be created in the
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pwmchipN directory it is associated with, where X is the number of the
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channel that was exported. The following properties will then be available:
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period - The total period of the PWM signal (read/write).
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Value is in nanoseconds and is the sum of the active and inactive
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time of the PWM.
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duty_cycle - The active time of the PWM signal (read/write).
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Value is in nanoseconds and must be less than the period.
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polarity - Changes the polarity of the PWM signal (read/write).
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Writes to this property only work if the PWM chip supports changing
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the polarity. The polarity can only be changed if the PWM is not
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enabled. Value is the string "normal" or "inversed".
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enable - Enable/disable the PWM signal (read/write).
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0 - disabled
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1 - enabled
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Implementing a PWM driver
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-------------------------
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‎drivers/pwm/Kconfig

+4
Original file line numberDiff line numberDiff line change
@@ -28,6 +28,10 @@ menuconfig PWM
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if PWM
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config PWM_SYSFS
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bool
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default y if SYSFS
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config PWM_AB8500
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tristate "AB8500 PWM support"
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depends on AB8500_CORE && ARCH_U8500

‎drivers/pwm/Makefile

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
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obj-$(CONFIG_PWM) += core.o
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obj-$(CONFIG_PWM_SYSFS) += sysfs.o
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obj-$(CONFIG_PWM_AB8500) += pwm-ab8500.o
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obj-$(CONFIG_PWM_ATMEL_TCB) += pwm-atmel-tcb.o
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obj-$(CONFIG_PWM_BFIN) += pwm-bfin.o

‎drivers/pwm/core.c

+23-2
Original file line numberDiff line numberDiff line change
@@ -274,6 +274,8 @@ int pwmchip_add(struct pwm_chip *chip)
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if (IS_ENABLED(CONFIG_OF))
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of_pwmchip_add(chip);
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pwmchip_sysfs_export(chip);
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out:
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mutex_unlock(&pwm_lock);
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return ret;
@@ -310,6 +312,8 @@ int pwmchip_remove(struct pwm_chip *chip)
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free_pwms(chip);
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pwmchip_sysfs_unexport(chip);
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out:
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mutex_unlock(&pwm_lock);
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return ret;
@@ -402,10 +406,19 @@ EXPORT_SYMBOL_GPL(pwm_free);
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*/
403407
int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
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{
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int err;
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405411
if (!pwm || duty_ns < 0 || period_ns <= 0 || duty_ns > period_ns)
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return -EINVAL;
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408-
return pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
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err = pwm->chip->ops->config(pwm->chip, pwm, duty_ns, period_ns);
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if (err)
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return err;
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pwm->duty_cycle = duty_ns;
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pwm->period = period_ns;
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return 0;
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}
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EXPORT_SYMBOL_GPL(pwm_config);
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@@ -418,6 +431,8 @@ EXPORT_SYMBOL_GPL(pwm_config);
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*/
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int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
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{
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int err;
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421436
if (!pwm || !pwm->chip->ops)
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return -EINVAL;
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@@ -427,7 +442,13 @@ int pwm_set_polarity(struct pwm_device *pwm, enum pwm_polarity polarity)
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if (test_bit(PWMF_ENABLED, &pwm->flags))
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return -EBUSY;
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430-
return pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
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err = pwm->chip->ops->set_polarity(pwm->chip, pwm, polarity);
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if (err)
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return err;
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pwm->polarity = polarity;
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return 0;
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}
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EXPORT_SYMBOL_GPL(pwm_set_polarity);
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