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Date: Thu, 23 Sep 2010 15:35:12 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Richard Purdie <rpurdie@rpsys.net>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] led-class: always implement blinking
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On Wed, 22 Sep 2010 15:53:58 +0200
Johannes Berg <johannes@sipsolutions.net> wrote:

> Currently, blinking LEDs can be awkward because it is
> not guaranteed that all LEDs implement blinking. The
> trigger that wants it to blink then needs to implement
> its own timer solution.
> 
> Rather than require that, add led_blink_set() API that
> triggers can use. This function will attempt to use hw
> blinking, but if that fails implements a timer for it.
> To stop blinking again, brightness_set() also needs to
> be wrapped into API that will stop the software blink.
> 
> As a result of this, the timer trigger becomes a very
> trivial one, and hopefully we can finally see triggers
> using blinking as well because it's always easy to use.
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> ---
> v2: - update documentation
>     - use documented way of turning blinking off
>       by setting brightness to 0 rather than by
>       setting delays to (0, 0)
>     - add API to start blinking, set brightness
>       (the latter will also stop sw blinking)
> v3: - make LEDS_CLASS a bool rather than tristate
>       because LEDS_TRIGGERS now depends on symbols
>       it exports

`make oldconfig' says

boolean symbol LEDS_CLASS tested for 'm'? test forced to 'n'