Hi, I recently bought new notebook (dell M4500) and noticed that acpi video cannot shut down LCD screen. Backlight control works just fine but I cannot completely turn off the display. I used to control display with: echo 0x80000000 > /proc/acpi/video/VID/LCD/state and it worked fine. On this notebook it just returns: bash: echo: write error: Bad address I even found new sysfs interface at /sys/class/backlight/acpi_video0/ but bl_power does nothing. Only thing in dmesg that seems related is this: [ 5.891839] ACPI: Video Device [VID1] (multi-head: yes rom: no post: no) uname -a: Linux gregy 2.6.34 #5 SMP PREEMPT Sun May 23 17:04:42 CEST 2010 x86_64 Intel(R) Core(TM) i7 CPU Q 820 @ 1.73GHz GenuineIntel GNU/Linux video card: nvidia quadro fx 880M please tell me what other information is needed. Thank you P.S. I couldn't find any kernel acpi documentation anywhere, am I blind?
What do you want to do? Turning off the display completely or just turn off the backlight? ACPI can only decrease the screen backlight to the minimum value that BIOS tells it. Sometimes this equals turning off the backlight while sometimes this just means dimming the screen. But this doesn't equal turning off the display. To turn off/on the display, you need to ask help for some graphics tools, say "xrandr --output LVDS --off"/"xrandr --output LVDS --auto". Anyway, this is not an ACPI problem, bug closed.