linux-kernel - Re: [PATCH 2/3] leds-clevo-mail: hw accelerated LED blink extension

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Message-Id: <1193176185.5709.140.camel@localhost.localdomain>
Date:	Tue, 23 Oct 2007 22:49:45 +0100
From:	Richard Purdie <rpurdie@...ys.net>
To:	Németh Márton <nm127@...email.hu>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-kernel@...r.kernel.org, Rodrigo Pereira <rodripe@...il.com>
Subject: Re: [PATCH 2/3] leds-clevo-mail: hw accelerated LED blink extension

On Sun, 2007-10-21 at 14:54 +0200, Németh Márton wrote:
> From: Márton Németh <nm127@...email.hu>
> 
> Extends the leds subsystem with a blink_set() callback function which can
> be optionally implemented by a LED driver. If implemented, the driver can use
> the hardware acceleration for blinking a LED.
> 
> Signed-off-by: Márton Németh <nm127@...email.hu>
> ---
> diff -uprN linux-2.6.23.orig/Documentation/leds-class.txt linux-2.6.23/Documentation/leds-class.txt
> --- linux-2.6.23.orig/Documentation/leds-class.txt	2007-10-09 22:31:38.000000000 +0200
> +++ linux-2.6.23/Documentation/leds-class.txt	2007-10-21 10:45:35.000000000 +0200
> @@ -47,6 +49,19 @@ overhead, I suggest these become part of
>  above leaves scope for further attributes should they be needed.
> 
> 
> +
> +Hardware accelerated blink of LEDs
> +==================================
> +
> +Some LEDs can be programmed to blink without any CPU interaction. To
> +support this feature, a LED driver can optionally implement the
> +blink_set() function (see <linux/leds.h>). If implemeted, the
> +ledtrig-timer tries to use it. The blink_set() function should return
> +0 if the blink setting is supported, or -EINVAL otherwise, which means
> +that the LED will be turned on and off from software by the leds
> +subsystem.

Hardware acceleration of the timer triggers is great to see and worst
case I'll happily apply this patch to the LED tree, thanks.

Before I do, I did wonder if we should enhance the meaning of the
set_blink function a bit. If set_blink is called with delay_on = 0,
delay_off = 0 it could mean "blink with some user friendly value,
hardware assisted". The use for this would be a more generic blink
trigger where you wouldn't need to know about magically hardware
assisted values for blinking, it would simply make an LED blink in a
hardware assisted way.

We also need to document that the brightness_set overrides any blinking
which may or may not be active (which is implied in your driver).

Cheers,

Richard


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