Commit Graph

8 Commits

Author SHA1 Message Date
Alexandre Belloni
4284402924 pwm: modify PWM_LOOKUP to initialize all struct pwm_lookup members
Now that PWM_LOOKUP is not used anymore, modify it to initialize all the
members of struct pwm_lookup.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
2014-05-21 11:19:36 +02:00
Thierry Reding
3e5314d3c8 pwm: Document signal polarity convention
The PWM subsystem defines normal and inversed PWM signal polarity in an
unambiguous way. In addition to the documentation in the linux/pwm.h
header file, add a paragraph in Documentation/pwm.txt because people are
likely to look there for guidance.

Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
2014-04-28 13:04:59 +02:00
Sachin Kamat
702e304f19 Documentation/pwm: Fix trivial typos
Fixes some trivial typos to improve readability.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
2013-10-24 10:51:33 +02:00
H Hartley Sweeten
76abbdde2d 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>
2013-06-21 11:32:51 +02:00
Alexandre Courbot
6354316dbe pwm: add devm_pwm_get() and devm_pwm_put()
Add resource managed variants of pwm_get() and pwm_put() for
convenience. Code is largely inspired by the equivalent devm functions
of the regulator framework.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
2012-09-10 17:05:45 +02:00
Thierry Reding
8138d2ddbc pwm: Add table-based lookup for static mappings
In order to get rid of the global namespace for PWM devices, this commit
provides an alternative method, similar to that of the regulator or
clock frameworks, for registering a static mapping for PWM devices. This
works by providing a table with a provider/consumer map in the board
setup code.

With the new pwm_get() and pwm_put() functions available, usage of
pwm_request() and pwm_free() becomes deprecated.

Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
2012-06-15 12:56:53 +02:00
Thierry Reding
f051c466cf pwm: Allow chips to support multiple PWMs
Many PWM controllers provide access to more than a single PWM output and
may even share some resource among them. Allowing a PWM chip to provide
multiple PWM devices enables better sharing of those resources. As a
side-effect this change allows easy integration with the device tree
where a given PWM can be looked up based on the PWM chip's phandle and a
corresponding index.

This commit modifies the PWM core to support multiple PWMs per struct
pwm_chip. It achieves this in a similar way to how gpiolib works, by
allowing PWM ranges to be requested dynamically (pwm_chip.base == -1) or
starting at a given offset (pwm_chip.base >= 0). A chip specifies how
many PWMs it controls using the npwm member. Each of the functions in
the pwm_ops structure gets an additional argument that specified the PWM
number (it can be converted to a per-chip index by subtracting the
chip's base).

The total maximum number of PWM devices is currently fixed to 1024 while
the data is actually stored in a radix tree, thus saving resources if
not all of them are used.

Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
[eric@eukrea.com: fix error handling in pwmchip_add]
Signed-off-by: Eric Bénard <eric@eukrea.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
2012-06-15 12:56:52 +02:00
Sascha Hauer
0c2498f166 pwm: Add PWM framework support
This patch adds framework support for PWM (pulse width modulation) devices.

The is a barebone PWM API already in the kernel under include/linux/pwm.h,
but it does not allow for multiple drivers as each of them implements the
pwm_*() functions.

There are other PWM framework patches around from Bill Gatliff. Unlike
his framework this one does not change the existing API for PWMs so that
this framework can act as a drop in replacement for the existing API.

Why another framework?

Several people argue that there should not be another framework for PWMs
but they should be integrated into one of the existing frameworks like led
or hwmon. Unlike these frameworks the PWM framework is agnostic to the
purpose of the PWM. In fact, a PWM can drive a LED, but this makes the
LED framework a user of a PWM, like already done in leds-pwm.c. The gpio
framework also is not suitable for PWMs. Every gpio could be turned into
a PWM using timer based toggling, but on the other hand not every PWM hardware
device can be turned into a gpio due to the lack of hardware capabilities.

This patch does not try to improve the PWM API yet, this could be done in
subsequent patches.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Matthias Kaehlcke <matthias@kaehlcke.net>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
[thierry.reding@avionic-design.de: fixup typos, kerneldoc comments]
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
2012-06-15 12:56:50 +02:00