Re: 2.6.21-rc2 radeon backlight

Henrique de Moraes Holschuh [off-list ref] writes:

On Fri, 02 Mar 2007, David Miller wrote:

quoted

Why don't we compromise for 2.6.21 by marking the Radeon backlight
stuff EXPERIMENTAL until the cases where IBM ACPI works and the
Radeon backlight stuff does not are worked out?

What ibm-acpi backlight control does is *very* different from what the
radeon backlight control does.

ibm-acpi talks to the ThinkPad EC to change the brightness of the backlight,
it has *NO* on/off support.  Radeon talks to the video chipset to turn the
LVDS output on/off (or something to that effect), and thus to turn the
backlight on/off.

if i don't enable the radeon backlight support the backlight works and
i can turn it on and off using radeontool. if i enable the radeon
backlight support the screen stays dark (although i can log on my
laptop remotely). if i try to use radeontool to turn the backlight on
nothing happens. so, at least on the thinkpad, the radeon backlight
support disables some other kind of backlight support that works
otherwise.

--alex--

-- 
| I believe the moment is at hand when, by a paranoiac and active |
|  advance of the mind, it will be possible (simultaneously with  |
|  automatism and other passive states) to systematize confusion  |
|  and thus to help to discredit completely the world of reality. |

From: Alex Romosan <redacted>
Date: Fri, 02 Mar 2007 13:22:27 -0800

if i don't enable the radeon backlight support the backlight works and
i can turn it on and off using radeontool. if i enable the radeon
backlight support the screen stays dark (although i can log on my
laptop remotely). if i try to use radeontool to turn the backlight on
nothing happens. so, at least on the thinkpad, the radeon backlight
support disables some other kind of backlight support that works
otherwise.

Right, that's the crux of the problem.

The Radeon backlight support conflicts somehow with the
way the ACPI code programs the same hardware, and until
we figure out exactly what's going on, this is a regression.

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