On 02/19/2013 08:27:41 AM, Lars Poeschel wrote:
From: Lars Poeschel <poeschel@xxxxxxxxxxx>
This adds a simple sysfs interface to the pwm subsystem. It is
heavily inspired by the gpio sysfs interface.
Docs!
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt
index 7d2b4c9..b349d16 100644
--- a/Documentation/pwm.txt
+++ b/Documentation/pwm.txt
@@ -45,6 +45,52 @@ 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().
Hm, read read read existing file...
So a PWM is a GPIO that blinks on its own, in hardware, without needing
a kernel thread and a timer to tell it to? (I think? Correction, an
output-only gpio...)
+Using PWMs with the sysfs interface
+-----------------------------------
+
+You have to enable CONFIG_PWM_SYSFS in your kernel configuration to
use
+the sysfs interface. It is exposed at /sys/class/pwm/. If there are
pwm
+drivers loaded and these drivers successfully probed a chip, this
chip
+is exported as pwmchipX . Note that a single driver can probe
multiple chips.
+Inside the directory you can read these properties:
+
+base - This is the linux global start where the chips pwm channels
get
+exposed.
+
+npwm - This is the number of pwm channels this chip supports.
+
+If you want to start using a pwm channel with sysfs first you have to
+export it. If you are finished with it and want to free the pwm for
other
+uses, you can unexport it:
+
+export - Write the global pwm channel number to this file to start
using
+the channel with sysfs.
+
+unexport - Write the global pwm channel number of the channel you
are finshed
+with to this file to make the channel available for other uses.
+
+Once a pwm is exported a pwmX (X ranging from 0 to MAX_PWMS)
directory appears
+with the following read/write properties inside to control the pwm:
+
+duty_ns - Write the number of nanoseconds the active portion of the
pwm period
+should last to this file. This can not be longer than the period_ns.
+
+period_ns - Write the length of the pwm period in nanoseconds to
this file.
+This includes the active and inactive portion of the pwm period and
can not
+be smaller than duty_ns.
+
+polarity - The normal behaviour is to put out a high for the active
portion of
+the pwm period. Write a 1 to this file to inverse the signal and
output a low
+on the active portion. Write a 0 to switch back to the normal
behaviour. The
+polarity can only be changed if the pwm is not running. This file is
only
+visible if the underlying driver/device supports changing the
polarity.
+
+run - Write a 1 to this file to start the pwm signal generation,
write a 0 to
+stop it. Set your desired period_ns, duty_ns and polarity before
starting the
+pwm.
+
+It is recommend to set the period_ns at first and duty_ns after that.
+
Implementing a PWM driver
-------------------------
Doc part looks good to me:
Acked-by Rob Landley <rob@xxxxxxxxxxx>
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index e513cd9..1c3432e 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -28,6 +28,21 @@ menuconfig PWM
if PWM
+config PWM_SYSFS
+ bool "/sys/class/pwm/... (sysfs interface)"
+ depends on SYSFS
+ help
+ Say Y here to add a sysfs interface for PWMs.
+
+ This exports directories and files to userspace using sysfs.
Given that that's what a sysfs interface _is_, does that last line
actually add anything?
+ This way the PWM outputs of a device can easyly be used,
s/easyly/easily/
+ controlled and tested.
And again, this sentence isn't hugely helpful if you already know what
sysfs is. Why not start here:
+ For every instance of an PWM capable
+ device there is a pwmchipX directory exported to
+ /sys/class/pwm. If you want to use a PWM, you have to export
+ it to sysfs, which is done by writing the number into
+ /sys/class/pwm/export. After that /sys/class/pwm/pwmX is
+ reaady to be used.
+
s/reaady/ready/
Rob--
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