Bug#424868: Noise from backlight electronics with new kernel 2.6.18 for PowerPC

[Moritz Muehlenhoff <jmm@inutil.org>]

On Thu, May 17, 2007 at 03:25:13PM +0200, Beat Zahnd wrote:
> Source: linux
> Version: 2.6
>
> After Updating to etch and kernel 2.6.18 a whining very high frequency
> noise is hearable. The same noise was also hearable with kernel-2.6.8
> but only if backlight intensity was not at maximum level
>
> As with the old kernel the noise frequency changes with backlight
> intensity change, but is not disapearing with maximum intensity with
> the new kernel. Upon boot the noise is not present until the line:
>
> pmubl: Backlight initialized (pmubl)
>
> appears. Therefore I think that the new kernel has limited the
> backlight level to value slighly bellow the hardware limit.
>
> The above stated console log line is issued by code in
>
> drivers/macintosh/via-pmu-backlight.c

Does this error still occur with more recent kernel versions?

If you're running Etch, could you try to reproduce this bug
with the 2.6.24 based kernel added in 4.0r4?
http://packages.qa.debian.org/l/linux-2.6.24.html

Cheers,
        Moritz