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. 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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