Re: rc6+ regression - backlight reset to 0 on boot after 7c0ea45be4f114d85ee35caeead8e1660699c46f

On Wed, 2008-04-02 at 22:53 +0400, Andrey Borzenkov wrote:
Commit 7c0ea45be4f114d85ee35caeead8e1660699c46f registers ACPI backlight
even if _BQC method (query current backlight level) is missing. The effect is:

during initialization video.c:acpi_video_device_find_cap() calls backlight_update_status(). It tries to fetch actual level via acpi_video_get_brightness() - but as _BQC is missing it just returns current value
as stored in memory - i.e. zero, because it was never set. So effectively
backlight_update_status() reset brightness to minimal value == 0.

This happens on Toshiba Portege 4000. Verified by reverting commit on top of
rc8.
It seems that _BQC object is missing on the Toshiba Portege 4000. And
acpi video driver will continue to update the status of backlight even
when _BQC object is missing, which is inappropriate.
Maybe it is more appropriate that OS doesn't update the status of
backlight in boot phase when _BQC object is missing.

Of course please attach the output of acpidump in kernel bugzilla.
http://bugzilla.kernel.org/show_bug.cgi?id=10387
On a side note, it would be nice to fit backlight device into actual ACPI
device tree instead of /devices/virtual.

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