I installed Slackware64-current (2.6.38.7 kernel) on a new HP Pavilion dv7t-6100 laptop. It works except that I'm unable to set the screen brightness. The brightness remains at maximum.

Pressing Fn+F2 or Fn+F3 causes the contents of

/sys/devices/virtual/backlight/acpi_video0/brightness
/sys/devices/virtual/backlight/acpi_video1/brightness

to change, but the screen brightness remains the same. dmesg gives the error:

Jun 9 18:28:26 dv7t logger: ACPI group video / action DD02 is not defined

Writing to the brightness files doesn't change the brightness.

I have tried pretty much every solution known to Google, including setting acpi_osi=Linux|Windows, acpi_backlight=vendor|hardware, and writing to the i915 hardware register via setpci. Upgrading to the 2.6.39.1 kernel doesn't fix the problem.

I note that on this laptop, the brightness keys don't work while in the BIOS or while Linux is booting, or even while in the Windows 7 recovery program. There seems to be some HP-specific driver that gets installed only on Windows 7.

Any suggestions?

A possibly related problem is that even though the 2.6.38.7 kernel recognizes and loads both the i915 and radeon drivers, and the vga_switcheroo sees both, regardless of the vga_switcheroo setting, the i915's output is always sent to the LCD and the radeon never sees an attached screen. I can live with this problem, but the screen brightness is a showstopper.
Ed

The kernel loads the hp_wmi (hotkeys) module, which I suspect may be part of the problem.

Two hotkeys work: the Fn+F12 key turns off the wireless, and Fn+Space toggles the trackpad LEDs.
Ed

A kernel bug has been filed https://bugzilla.kernel.org/show_bug.cgi?id=38342 that may address this problem.

The hardware is different (a Sony laptop with Arrandale/IronLake versus my HP laptop with Sandy Bridge), but the symptoms are very similar.
Ed

For the dv7's and probably also envy computer from hp, check the bios settings. It defaults the F keys to be used without pressing the Fn key. Go to the bios and set it to work when Fn is pressed.

Wayne Sallee
Wayne@WayneSallee.com

The brightness can't be changed regardless of the Fn hotkey setting in the BIOS.

The brightness hotkeys don't work anyway while in the BIOS setup. This is the first laptop I've owned whose BIOS couldn't change the brightness.
Ed

My dv7 brightness keys work while under Mandriva Linux.

Is your right mouse click on the ClickPad working?
Mine doesn't under Mandriva, but barely does under Fedora. Different flavors of Linux come up with different solutions, it would be nice if we could benefit from other's fixes sooner.

Wayne Sallee
Wayne@WayneSallee.com

The problem occurs on the newest version of the dv7, the 6100. HP has been selling this model for only for about the past two months.

The trackpad works fine. Actually, all the hardware devices work under Linux with the exception of the backlight control and discrete graphics.
Ed

You might want to look at /var/log/messages and see if you are getting any other group action not defined errors.

Wayne Sallee
Wayne@WayneSallee.com

Good news - the i915 hardware backlight control does work. I developed a patch to the Linux kernel that initializes the i915 backlight registers http://www.edgrochowski.com/articles/backlight.htm

This should be useful on machines with non-functional BIOS backlight controls. I'm marking the thread as solved.
Ed