No backlight since linux-4.2.4 - drivers/gpu/drm/radeon/atombios_encoders.c

[Michel Dänzer]

On 25.10.2015 04:25, Michael Burian wrote:
> hi,
> 
> after updating the kernel from linux-stable[0] v4.2.3 to v4.2.4 on my
> hp compaq nx9420 laptop (Debian Jessie, amd64), the backlight is turned off
> within the first couple of seconds during boot.
> 
> The situation persists (Xorg seems to be running fine, icons can be recognized
> by illuminating the screen with a flashlight) until reboot using an earlier
> kernel.
> 
> current mainline[1] as of now (4.3.0-rc6-00277-g01815536) is also affected
> 
> Workaround: use earlier kernel (v4.2.3) or (see below)
> 
> Hardware:
> 
> lspci | grep adeo
> 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV530/M56-P [Mobility Radeon X1600]
> 
> git bisect log
> # bad: [190bd21bba09ed476d9359d3e8be20e8d9dcd8a4] Linux 4.2.4
> # good: [fcba09f2b0bf27eeaa1d4d439edb649585f35040] Linux 4.2.3
> git bisect start 'v4.2.4' 'v4.2.3' 'drivers/gpu/'
> # good: [885838eef785ff810dac945be8132856f2113cf1] drm/amdgpu: make UVD handle checking more strict
> git bisect good 885838eef785ff810dac945be8132856f2113cf1
> # good: [230f6fd628c83fcb44ea364d69a9ad88826ef8c4] drm/i915/bios: handle MIPI Sequence Block v3+ gracefully
> git bisect good 230f6fd628c83fcb44ea364d69a9ad88826ef8c4
> # bad: [5a633828b4b2bef343826afcb0a70770c4911c55] drm/radeon: Restore LCD backlight level on resume (>= R5xx)
> git bisect bad 5a633828b4b2bef343826afcb0a70770c4911c55
> # good: [60a09aef456ef590762d47da9c25650e230e2f85] drm: Reject DRI1 hw lock ioctl functions for kms drivers
> git bisect good 60a09aef456ef590762d47da9c25650e230e2f85
> # first bad commit: [5a633828b4b2bef343826afcb0a70770c4911c55] drm/radeon: Restore LCD backlight level on resume (>= R5xx)
> 
> Workaround 2:
> 
> reverting this single commit 5a633828b4b2bef343826afcb0a70770c4911c55 fixes the problem in linux-stable[0]
> as well as mainline[1] 4.3.0-rc6-00277-g01815536

Please provide the dmesg output from running with the attached debugging
patch.


Alex, any other ideas what might go wrong?


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer
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