[SOLVED] Display backlight hotkeys do not function on Precision 5510 - FIX add Dell WMI drivers to kernel

Try reverting to the previous BIOS.  I found A10 to be very unstable, particularly with respect to the backlight and suspend/resume.

Thanks gregbunk, I feel like we have a couple of threads that are effectively conversations between the two of us.  I'll try downgrading my BIOS but I'm trying to list specific issues that I find to elicit feedback from other users and/or the Sputnik team members on the forum.  Some of these are not insignificant bugs, is only affecting those of us who are not running Ubuntu?  Have Dell employees using these laptops not noticed these issues?  With something like the issue that I am facing with my brightness hotkeys, even if it is a bug, it should be something that's predictably reproducible.  Even if irritating I would appreciate if someone with more knowledge of the laptop's hardware, software and BIOS could provide some information on a reliable technique to bypass the bug.  Even bugs aren't "random".

More generally, while I recognize that I am running an unsupported software configuration, it would be nice to at least receive a confirmation of whether others are experiencing similar issues (or not) when running Dell's supported Ubuntu release or other software.  I rather feel like I'm shouting in the wind with these bug reports and questions apart from confirmations that you are facing similar bugs with the A10 BIOS.  This computer was a substantial investment and while I'm generally happy with it, being ignored after purchase leaves a somewhat bitter taste in the mouth.

I seem to have been able to isolate this issue somewhat.  It doesn't seem to be related to the BIOS version, I tried downgrading to A07 and had the same issue.

The problem seems to be BIOS related though.  The intermittent functioning of the hotkeys seems to be related to the kernel parameters that I am passing through the bootloader.  Either passing no acpi_osi value or acpi_osi=Linux (or even acpi_osi='!Windows 2012') causes this intermittent hotkey functioning.  I tried various permutations of acpi_backlight and video.use_native_backlight values with the acpi_osi values but continued to experience only "random" boots when the hotkeys worked.  (I did however notice that booting with the acpi_backlight option once produced explicit "BACKLIGHT" values in xev when the hotkeys worked).

However, when I boot with acpi_osi= (with no value) the hotkeys work but they appear to bypass the OS and directly adjust the brightness.  This is to say that the OSD and the OS widgets do not reflect the changes to brightness that I do with the hotkeys.  The hotkeys do not register any values under xev.  Using the hotkeys to change the brightness only changes the actual_brightness value under sysfs but does not touch the brightness value.  This results in an odd "competition" between the OS brightness settings and the hotkeys.  Adjusting the brightness using the OS widgets will adjust both brightness and actual_brightness but this will ignore the relative point that the hotkeys set and vice versa.  For example, if I lower my brightness to 2 using my hotkeys but then drag my OS widget slider from 100% to 50% the brightness will "jump" to 100% as soon as I interact with the OS widget and then settle at a value of 6 when I finish sliding.  If I subsequently press the brightness up hotkey, the brightness will actually drop from 6 to 3 as the hotkey adjustment "remembers" that it was previously set to 2 and increases the brightness one step from there.

While it is nice to have the hotkeys working again in a reliable fashion, it would be great it I could sort this out to have consistent behavior between the laptop hardware and software.  Any ideas? 

This problem was occurring because I didn't compile the DELL WMI drivers in the kernel (or as a module).  Setting CONFIG_DELL_WMI fixed the issue for me.