linux-kernel - Re: 2.6.21-rc2 radeon backlight

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Date:	Sat, 03 Mar 2007 16:35:13 +0000
From:	Richard Purdie <rpurdie@...ys.net>
To:	James Simmons <jsimmons@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Antonino A. Daplas" <adaplas@...il.com>,
	Alex Romosan <romosan@...orax.lbl.gov>,
	linux-kernel@...r.kernel.org,
	linux-fbdev-devel@...ts.sourceforge.net,
	"David S. Miller" <davem@...emloft.net>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Yaroslav Halchenko <lists@...russian.com>
Subject: Re: 2.6.21-rc2 radeon backlight

On Sat, 2007-03-03 at 16:06 +0000, James Simmons wrote:
> > > Richard, is this actually a bug, or is it a config error or something like that?
> > > 
> > > And should we track it as a post-2.6.20 regression?
> > 
> > Its a regression IMO. Arguably its a Kconfig error but a nasty one as
> > the defaults cause the problems. Different people seem to have different
> > interpretations but to me it appears that the patch from James causes
> > backlights to fail to turn on for a variety of devices which worked
> > before.
> 
>    It is NOT a Kconfig error. The problem is that for many fbdev drivers 
> the backlight code is broken. For some magic reason it only works on 
> pmacs. Most likely because the firmware properly sets up the backlight. 
> Plus we have the conflict with acpi backlight. 
>    Think about it. Enabling the backlight code breaks the backlight. 
> Without the backlight driver the default behaviour of the backlight works.
> Who sets up the default behavior? I don't have a LCD panel with a 
> backlight othewise I would track the problem down.

I not arguing several fb driver's backlight code isn't broken, it is. We
have a Kconfig problem though since we used to stop users selecting
things that didn't work and now we're allowing them. Worse still, the
defaults break for people. That is a regression.

Anyhow, the patch I proposed should let people enable/disable it at
runtime with defaults known to work which should address the problem
until someone figures out how to fix the backlight drivers themselves
properly.

Cheers,

Richard

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