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pwm: Add sysfs interface

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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>
This commit is contained in:
H Hartley Sweeten
2013-06-11 10:38:59 -07:00
committed by Thierry Reding
parent 3dd0a90947
commit 76abbdde2d
7 changed files with 524 additions and 3 deletions
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Documentation/pwm.txt
+37
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@@ -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
-------------------------