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author | H Hartley Sweeten <hartleys@visionengravers.com> | 2013-06-11 19:38:59 +0200 |
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committer | Thierry Reding <thierry.reding@gmail.com> | 2013-06-21 11:32:51 +0200 |
commit | 76abbdde2d95a3807d0dc6bf9f84d03d0dbd4f3d (patch) | |
tree | 63a5476d6fbf80ec90b813461ec7ec67ff462684 /Documentation/pwm.txt | |
parent | pwm: Fill in missing .owner fields (diff) | |
download | linux-76abbdde2d95a3807d0dc6bf9f84d03d0dbd4f3d.tar.xz linux-76abbdde2d95a3807d0dc6bf9f84d03d0dbd4f3d.zip |
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>
Diffstat (limited to 'Documentation/pwm.txt')
-rw-r--r-- | Documentation/pwm.txt | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt index 7d2b4c9b544b..1039b68fe9c6 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 ------------------------- |