Backlight brightness problem on HP Compaq 8710p

Bug #308784 reported by Stanislaw G. on 2008-12-16
Affects Status Importance Assigned to Milestone
Gentoo Linux
acpi-support (Ubuntu)

Bug Description

I've got HP 8710p laptop with Ubuntu 8.10 intrepid, Kernel 2.6.27-9-generic and GNOME 2.24.1
My video card is NVIDIA Quadro NVS 320M using 173.14.12 driver version

Everything still works fine except backlight brightness adjustment, and my problem is interesting and differs from previous bug reports posted by others.

I can adjust brightness before Ubuntu is loaded (e.g. in grub loader or bios settings) by pressing Fn+F9/F10, that means these are hardware keys, right?

When I go to Power Management, i see "Set display brightness to:" slider, but moving it does no changes to backlight brightness.

When I press Fn+F9/F10 keys to adjust brightness, I see the adjustment bar at the bottom of my screen, showing more or less brightness when I press keys, but actually no changes is being made to it. Doing this, I watch the output of "cat /proc/acpi/video/C14B/C15F/brightness", and the "current" value changes correctly on keys pressing.

When I exit to console (by pressing Ctrl+Alt+F1), I'm able to change brightness fine with my keys, and when I go back to GNOME (pressing Alt+F7) the brightness remains as I've set it in console, and "cat /proc/acpi/video/C14B/C15F/brightness" displays correct corresponding "current" value. And again, being in GNOME and pressing my brightness keys, I'm able to change this "current" value, but no changes are actually made to backlight.

I've searched all over the Internet for my issue, but could not find anything, the most of other issues are about unability to change that "current" value with the keys, but as you see I have some other problem.

I'm a little newbie in Linux, so if you need any logs or some extra information, I'll be glad to add it to my post.

Any help and replies would be appreciated.

Stanislaw G. (regent-elite) wrote :

i don't exactly know whom i should assign this report to

Zhang Rui (rui-zhang) wrote :

please download the latest pmtools at
make, and run "./acpidump > acpidump.log"
and attach the acpidump.log here.

In Gnome, please make sure if you can change the backlight by
poking the "/sys/class/backlight/*/brightness"

Stanislaw G. (regent-elite) wrote :

Here is acpidump.log that you requested

executing "echo -n 1 > /sys/class/backlight/acpi_video0/brightness" or "echo -n 5 > /sys/class/backlight/acpi_video0/brightness" sets this brightness value to 1 or 5 (from 10 available), but this change does not affect the actual backlight lamp brightness

when I'm trying to change brightness with my Fn+F9/F10 keys, I see the adjustment bar at the bottom of my screen, showing more or less brightness depending on key pressing, and value in "/sys/class/backlight/acpi_video0/brightness" is changing correctly, but no actual effect

Stanislaw G. (regent-elite) wrote :

BTW, when I exit to console using Ctrl+Alt+F1 and then execute

"echo -n 1 > /sys/class/backlight/acpi_video0/brightness"
"echo -n 30 > /proc/acpi/video/C14B/C15F/brightness"

all works fine.

It seems to me that my Function keys (Fn+F9/F10) work fine and pressing them changes the brightness value correctly, but I feel that this value isn't read in GNOME by some other module that operates a backlight lamp or something like this. Outside the GNOME it all works fine. I don't know if it is a GNOME issue or X server issue or what else it can be

Stanislaw G. (regent-elite) wrote :

Has anybody got any ideas on the issue?

When I use VESA driver, I can control brightness as it should be.
Does it mean that there's a problem in my NVIDIA driver?

Zhang Rui (rui-zhang) wrote :

I suspect it a Nvidia driver problem rather than an ACPI bug.

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