linux-kernel - Re: [PATCH 1/1] PXAFB: Support for backlight control

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Date:	Thu, 22 Feb 2007 12:33:35 +0200
From:	Paul Sokolovsky <pmiscml@...il.com>
To:	Rodolfo Giometti <giometti@...eenne.com>
CC:	linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org,
	<linux-fbdev-devel@...ts.sourceforge.net>,
	Richard Purdie <rpurdie@...ys.net>
Subject: Re: [PATCH 1/1] PXAFB: Support for backlight control

Hello Rodolfo,

Thursday, February 22, 2007, 10:32:04 AM, you wrote:

> On Wed, Feb 21, 2007 at 06:26:08PM +0200, Paul Sokolovsky wrote:
k>>   Why? It's the same, except that it already exists, generic one (not
>> limited to pxafb), and requires 1 function (too bad that C doesn't
>> support lambda's):

> Ah, ok.

>>   I sent a bit of criticism for that too ;-). YMMV, but kernel
>> solutions are just bound to be pretty simple and generic and lack
>> any "niceties", which you'd likely want to do anyway eventually. For
>> example, what if you'll want to implement "fade out" effect for
>> keyboard backlight? Doing it in adhoc manner in kernel? Whereas with
>> the LCD classdev, you can write generic "fade out" trigger and
>> attach/detach it from userspace.

> I agree. I just wish to add a backlight support for my LCD and
> minikeypad.

> What do you suggest to me in order to accomplish such task?

  Well, I write exactly to share experience and work towards having
best practices for backlight, etc. control, reusable on wide range of
embedded/handheld devices.

  We in handhelds.org codebase have attached patch* to make corgi_bl
more suitable for general use. This patch was submitted to Richard
(so, more votes needed ;-) ). Otherwise, snippet I pasted is from real
machine implementation, HP iPaq h4000.

  As for keyboard backlight, another port we have, HTC Universal, has:
normal indicator LEDs, keyboard backlight, flashlight, ring vibra. All
of these are handled via Generic LED API:
http://handhelds.org/cgi-bin/cvsweb.cgi/linux/kernel26/arch/arm/mach-pxa/htcuniversal/htcuniversal_leds.c?rev=1.6&content-type=text/x-cvsweb-markup

  To show that it is not an anomaly, but hopefully, a trend, here's
vibra driver for the upcoming OpenMoko phone:
http://wiki.openmoko.org/wiki/Neo1973_Hardware#Vibrator

  So, if you have freedom to add keyboard backlight control to your
userspace, that would allow you to do many interesting things without
disturbing the kernel.

[*] Optimized for size, full one should patch <asm/arch/sharpsl.h> of
course.

> Thanks for your suggestions,

> Rodolfo

-- 
Best regards,
 Paul                            mailto:pmiscml@...il.com
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