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I have NX7400 laptop. Afer power up display backlight is always set to
100% light, independent of brightness settings in previous session. I
detected that problem is in acpi kernel driver video.ko and gnome-power-
manager. I use ubuntu 8.10 with kernel 2.6.27-7-generic on 64-bit
platform. This is a regression bug, because in previous version ubuntu
8.04LTS display backlight works ok.
Aditional comments:
I detected that acpi/video.ko kernel 2.6.24 driver in ubuntu 8.04
didn't work and backlight was controlled only by ACPI bios, because
/proc/bus/acpi/video/*/backlights always return that backlight is not
supported. In kernel 2.6.27 driver return correct backlight values:
cat /proc/acpi/video/C085/C144/brightness
levels: 100 51 30 37 44 51 58 65 72 79 86 93 100
current: 65
New video driver trying to get current backlight level from ACPI BQI
object but it is optional ACPI function. When ACPI does not support BQI
object driver will set back-light to maximum value. Pls. see code
video.c bellow:
if (device->cap._BQC)
device->backlight->props.brightness =
acpi_video_get_brightness(device->backlight);
else
device->backlight->props.brightness =
device->backlight->props.max_brightness;
backlight_update_status(device->backlight);
When ACPI BQI is not supported video.ko or gnome-power-manager should save and
restore current backlight value from config file.
Workaround:
Currently I workaround this problem by change kernel driver video.ko to
set 50% backlight when BQI object is not found (Pls see patch bellow). I
alse changed gnome-power-manager settings by run gconf-editor and set
following configuration values in /apps/gnome-power/manager/backlight by
changing keys values to:
brightness_ac = 50
brightness_battery = 30
brightness_dim_battery = 30
but it is obvious workaround.
** Affects: gnome-power-manager (Ubuntu)
Importance: Undecided
Status: New
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display brightness is setup to 100% after power up
https://bugs.launchpad.net/bugs/291742
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