Bug 65377

Summary: Backlight control via /sys/class/backlight/radeon_bl0 not working
Product: DRI Reporter: Bastian Triller <bastian.triller>
Component: DRM/RadeonAssignee: Default DRI bug account <dri-devel>
Status: RESOLVED FIXED QA Contact:
Severity: normal    
Priority: medium    
Version: XOrg git   
Hardware: x86-64 (AMD64)   
OS: Linux (All)   
Whiteboard:
i915 platform: i915 features:
Attachments:
Description Flags
don't register a radeon backlight none

Description Bastian Triller 2013-06-04 20:40:37 UTC 
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.
Comment 1 Alex Deucher 2013-06-04 21:05:38 UTC 
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.
Comment 2 Bastian Triller 2013-06-04 21:32:02 UTC 
(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?
Comment 3 Alex Deucher 2013-06-04 21:40:23 UTC 
(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.
Comment 4 Henri Verbeet 2013-06-05 12:28:38 UTC 
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.
Comment 5 Alex Deucher 2013-06-06 22:32:41 UTC 
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.
Comment 6 Bastian Triller 2013-06-07 05:28:45 UTC 
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.
Comment 7 Bastian Triller 2013-06-09 19:46:19 UTC 
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.
Comment 8 Alex Deucher 2013-06-10 14:01:43 UTC 
Created attachment 80624 [details] [review]
don't register a radeon backlight

This patch should skip adding a radeon backlight interface on your mac.
Comment 9 Bastian Triller 2013-06-16 20:21:16 UTC 
yes, /sys/class/backlight/radeon_bl0 device is gone.

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