• Sascha Hauer's avatar
    pwm: Add PWM framework support · 0c2498f1
    Sascha Hauer authored
    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: default avatarSascha Hauer <s.hauer@pengutronix.de>
    Acked-by: default avatarKurt Van Dijck <kurt.van.dijck@eia.be>
    Reviewed-by: default avatarArnd Bergmann <arnd@arndb.de>
    Reviewed-by: default avatarMatthias Kaehlcke <matthias@kaehlcke.net>
    Reviewed-by: default avatarMark Brown <broonie@opensource.wolfsonmicro.com>
    Reviewed-by: default avatarShawn Guo <shawn.guo@linaro.org>
    [thierry.reding@avionic-design.de: fixup typos, kerneldoc comments]
    Signed-off-by: default avatarThierry Reding <thierry.reding@avionic-design.de>
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