Comment Re:Why do Windows programs just run? (Score 2) 126
This has been a perpetual problem on my Lenovo W510. In one release, it did multiple steps, in the next one, no backlight control at all. I add some kernel command line options and get a crappy 4 step backlight. In the next release, I have to remove those options because my backlight didn't turn on at all with them. Now no working backlight controls (using the FN+Home/End combo on my laptop keyboard). I poke in the
There are lots of proposed fixes that would just resolve it, but they can't be accepted because they break userspace. The whole problem stems from the Laptop bios. In some cases, the bios will advertise ACPI methods to control the backlight, while the GPU driver exposes the controls as well. Depending on the particular bios version (and sometimes even bios settings), the keypress might, in bios, change the brightness, then report the keypress, or it might report the keypress and depend on the OS to use the ACPI interface to control the backlight, or it might depend on the OS to use the GPU driver interface to control the backlight. On some of the systems, the ACPI interface is sometimes broken, and on some, there are multiple controls (for display port and all the other possible display connections built into the system) with no clear way to determine which one to actually use. Some bioses report to work with 'Windows 2012' but actually completely don't. Some ONLY work with that, but report they work with older ones.
From what I recall of the discussion, Windows 8 deals with this by punting the actual event handling to the GPU drivers, expecting them to know how to handle the hardware.
Similar bugs can be seen in Windows if your run a newer version on hardware designed for a previous version (I saw this running Windows 7 on hardware designed for Windows XP, an old Dell laptop).
I find it kinda crazy that every single other feature of my laptop works perfectly (FIngerprint reader, color calibration, wimax radio {none of which I actually ever use}) while backlight which seems so simple (Press button, change brightness) is in a perpetual state of brokenness.