display brightness is setup to 100% after power up

[lucck]

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 also 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.

[Scott Howard (showard314)]

Thank you for your bug report and working to make Ubuntu better. This bug is currently under discussion at bug #35223, so I'll mark this bug as a duplicate of that one. I'm going to post your work that you did so far over there, but if you have anything to add in addition, please feel free to add it and report any additional bugs you find.