path: root/Documentation/pwm.txt
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Diffstat (limited to 'Documentation/pwm.txt')
1 files changed, 37 insertions, 0 deletions
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index 7d2b4c9b544..1039b68fe9c 100644
--- a/Documentation/pwm.txt
+++ b/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