This is a Macbook pro 8,2 with an Intel HD Graphics 3000 [8086:0116] and an AMD Radeon HD 6750M [1002:6741]. The backlight interface in /sys/class/backlight/radeon_bl0 does not work. Echoing to "brightness" does not change the brightness of the Monitor. There is also an apple_gmux interface, which works though. I've bound xbacklight to the brightness keys to control the brightness, but it looks like it's confused about which interface it should use: $ xbacklight -inc 5 No outputs have backlight property When I disable the Radeon card on boot and use the Intel card, xbacklight works.
If you are booting in EFI mode, does it work if you boot in legacy bios mode? Since it's a mac, it probably requires some mac specific hack.
(In reply to comment #1) > If you are booting in EFI mode, does it work if you boot in legacy bios > mode? Since it's a mac, it probably requires some mac specific hack. I'm booting via EFI stub. I'm not sure how to boot the bios emulation mode. Is it possible to plug in a usb stick with a "normal" live system to boot in emulation mode?
(In reply to comment #2) > I'm booting via EFI stub. I'm not sure how to boot the bios emulation mode. > Is it possible to plug in a usb stick with a "normal" live system to boot in > emulation mode? I'm not sure.
I think it depends a bit on the specific model, but many Macs will only boot EFI from USB. Refind (http://www.rodsbooks.com/refind/index.html) is potentially a way around that, although I'm not entirely sure if that counts as booting in EFI mode or in BIOS mode.
I believe the only way to control the backlight on the macs with multiple GPUs is via the gmux driver. Seems to be a mac specific thing.
Booting a dd'ed image did not work. I'll have to find a disc to test it. Looking into the xbacklight I saw that xbacklight tries to find a Backlught property on the output. xrandr lists this property on the intel output, but not on the radeon output.
The problem also exists if I boot in bios mode. I didn't mention that, when using the intel card there only is the apple_gmux interface.
Created attachment 80624 [details] [review] don't register a radeon backlight This patch should skip adding a radeon backlight interface on your mac.
yes, /sys/class/backlight/radeon_bl0 device is gone.
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.