Uncontrollable brightness with Ubuntu 12.10 on HP Pavilion g7-2220 Notebook

[Uncuddly]

Hello!

I recently received a new HP Pavilion g7-2220 Notebook PC and have loaded Ubuntu 12.10 onto it as an alternative to its native Windows 8. The results are mostly good or at least tolerable but the display is always at full brightness while using Linux.

Neither the notebook's brightness keys nor the slider in Ubuntu's "Brightness and Lock" settings have any effect on it. Google reveals that users in similar situations have had success adding "acpi_backlight=vendor" to grub but this only results in the brightness slider vanishing from settings.

Although I'm not sure what influence it might have over the screen brightness, the system reports that an AMD Radeon HD 7520G is responsible for its graphics. For what it's worth, the laptop's other hardware buttons (volume, media pause, wireless on/off) work as expected. I can switch back to Windows 8 to verify that the brightness is normally changeable, so it's not that the display itself is unable to dim. Any advice or suggestions in this regard would be greatly appreciated!

Suppose I could just wear sunglasses.

[Toz]

Hello and welcome to the forums.

Have you installed the ATI proprietary graphics drivers? You can find them by opening up the Software Centre, navigating to Edit->Software Sources and looking on the Additional Drivers tab.

You might also want to try the acpi_osi=Linux kernel parameter instead of "acpi_backlight=vendor".

[Uncuddly]

Thank you for the reply! I had not installed any proprietary software so I selected the fglrx driver at your suggestion. A fglrx-updates driver was also available but I decided to try them from the top down. Unfortunately, the result is that the laptop does not make it to login. It displays the end of the boot sequence as white text on a black screen.

I'm not sure whether returning to the open driver is best accomplished by means of booting in recovery mode or with the live DVD. I can't spend time with it at the moment, but once I figure it out I'll try the other proprietary driver and the proposed parameter.

In the meantime, thanks again for the feedback.

[Uncuddly]

Ok, so recovering from the previous attempt ended up being a fair mess. I couldn't boot far enough to reach a command line to potentially uninstall the problem driver and try again, so I used the Ubuntu DVD in an attempt to reinstall to get default settings. Sadly, the option to reinstall over the existing Ubuntu installation apparently doesn't like skipping the partitioning portion of the install, even though it would seem that no partition changes would be needed. So that reinstall got stuck after erasing enough of the original install that it couldn't be recognised and I had to do another reinstall over the Ubuntu partition.

Once Ubuntu was reinstalled, I tried the option for the updated proprietary driver. This has the same result of making the system unresponsive, so I suppose I'll have to reinstall Ubuntu again unless there is a less aggressive way to manipulate the installation without access to the command line. Maybe text-editing files with the DVD's OS? I'm not sure it's less trouble overall.

I'm not up for another reinstall tonight (also not sure that I haven't made an even bigger mess with my previous reinstall follies), so I still haven't been able to test the suggested parameter. The proprietary drivers aren't getting us anywhere on the brightness issue, anyway!

[Uncuddly]

After another reinstall, I tried the acpi_osi=Linux parameter. This does not restore control over brightness and has the side effect of disabling the other hardware keys, which previously worked. It also seemed to make the keyboard entirely unresponsive a few times as I tried to test the hardware buttons, requiring a restart. Maybe that was a consequence of the button pressing itself, though.

I should note that by default, without any acpi additions to grub, pushing the brightness buttons does cause Ubuntu's brightness indicator to appear and shift in the appropriate direction. It just doesn't affect screen brightness.

In summary, the proprietary drivers and grub changes aren't getting us anywhere on the HP g7-2220's brightness. It's fairly recent hardware so I expected it to have trouble with Linux, but one is duty-bound to try it so that the next person with one of these systems has something to read. On the bright side, I'm getting used to the maxed out screen setting.

[Toz]

Can you open a terminal window, run the following command and post back the results (it will identify your backlight interfaces):

for i in /sys/class/backlight/*; do echo $i; cat $i/brightness; cat $i/max_brightness; done

Maybe we can manually manipulate the brightness.

[Uncuddly]

The output is:

/sys/class/backlight/acpi_video0
6
10

Changing the brightness setting in Ubuntu changes the middle number. Since I have removed the grub changes, pressing the button to reduce brightness changes the 6 to 4, for example. Screen brightness obviously remains much higher than that!

Thanks for the continued feedback!

[Toz]

Hmmm. Can you retry this with the acpi_backlight=vendor parameter?
And can you also post back the results of:

lspci | grep VGA

It always seems to take some time with newer hardware to get functional support in the Linux kernel. I want to see if we can get a workaround to dim your brightness in the meantime.

[josvanr]

I'm following this discussion with great interest as I have the same problem on my HP Envy 17 (1.5 year old hardware)....

josvanr

[Uncuddly]

Retrying the above for-loop with the backlight parameter yields:

/sys/class/backlight/*
cat: /sys/class/backlight/*/brightness: No such file or directory
cat: /sys/class/backlight/*/max_brightness: No such file or directory

It's just an empty directory now that the parameter is set.

The result of lspci | grep VGA is:

00:01.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Trinity [Radeon HD 7520G]

Thanks for the interest, josvanr! I'm sure a solution will arise eventually!