linux-kernel - Re: [PATCH 1/2] PWM: add pwm framework support

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Date:	Wed, 29 Jun 2011 21:47:22 +0200
From:	Matthias Kaehlcke <matthias@...hlcke.net>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Arnd Bergmann <arnd@...db.de>,
	viresh kumar <viresh.kumar@...com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Ryan Mallon <ryan@...ewatersys.com>,
	Kurt Van Dijck <kurt.van.dijck@....be>,
	Lothar Waßmann <LW@...O-electronics.de>
Subject: Re: [PATCH 1/2] PWM: add pwm framework support

El Wed, Jun 29, 2011 at 11:03:34AM +0200 Sascha Hauer ha dit:

> 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@...gutronix.de>

Reviewed-by: Matthias Kaehlcke <matthias@...hlcke.net>

-- 
Matthias Kaehlcke
Embedded Linux Developer
Amsterdam

            You must have long-range goals to keep you from
                being frustrated by short-range failure
                                                                 .''`.
    using free software / Debian GNU/Linux | http://debian.org  : :'  :
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