[Bisected] No HDMI at 6.6.2 onward
Brief summary of the problem:
There is no HDMI display after 6.6.1.
git bisect
reports "first bad commit: [c76e483cd916] drm/amd/display: Don't restrict bpc to 8 bpc".
Reverting this patch fixes it for 6.6.3 and 6.6.4 (6.6.2 not tested).
Hardware description:
- CPU: AMD A6-9220 RADEON R4, 5 COMPUTE CORES 2C+3G
- GPU: Advanced Micro Devices, Inc. [AMD/ATI] Stoney [Radeon R2/R3/R4/R5 Graphics] [1002:98e4] (rev ea)
- System Memory: 16GiB
- Display(s): laptop, Dell U2711
- Type of Display Connection: eDP, HDMI
- Laptop: HP model 15-bw040AU, Product Id 1ZH49PA#ABG
System information:
- Distro name and Version: Slackware 15.0
- Kernel version: 6.6.4
-
- Custom kernel: N/A
- AMD official driver version: N/A
How to reproduce the issue:
With laptop powered off, select HDMI on the Dell U2711 display. Power button flashes yellow (power save / no signal). Power on and boot laptop. Kernel video starts (resolution changes from 80x25 to 170x48).
EXPECTED: Power button turns steady blue; backlight comes on, VT console displays after a few seconds.
ACTUAL: Power button turns steady blue; backlight comes on; message "Entering Power Save Mode" appears after a few seconds; power button may flash yellow; power button turns steady blue; cycle repeats.
Behaviour is much the same when running X except display was OK with
xrandr --output HDMI-A-0 --mode 1024x768 --same-as eDP
xrandr --output eDP --mode 1024x768
in effect, which is why I didn't notice the bug earlier.
Screenshots/video files
xrandr:
Screen 0: minimum 320 x 200, current 3286 x 1080, maximum 16384 x 16384
eDP connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 344mm x 193mm
1366x768 60.02*+ 40.01
1280x720 60.02
1024x768 60.02
800x600 60.02
640x480 60.02
HDMI-A-0 connected 1920x1080+1366+0 (normal left inverted right x axis y axis) 597mm x 336mm
1920x1080 60.00*+ 60.00 50.00 59.94 24.00 23.98
1600x1200 60.00
1680x1050 59.88
1280x1024 75.02 60.02
1440x900 60.00
1280x800 59.91
1152x864 75.00
1280x720 60.00 50.00 59.94
1024x768 75.03 60.00
800x600 75.00 60.32
720x576 50.00
720x480 60.00 59.94
640x480 75.00 60.00 59.94
720x400 70.08
DisplayPort-0 disconnected (normal left inverted right x axis y axis)