AMD A8 3500M LVDS (CH7511B) goes OFF after resolution change (randomly)
Brief summary of the problem:
Hello all, I'm using an AMD A8-3500M with AMD Radeon HD 6620G. I'm testing with several recent kernels (5.11 , 5.13) on different distros (Ubuntu, Tinycore). On all of them I have the same issue. When the video resolution change (for instance with xrandr --fb 1920x1079) sometimes LVDS won't turn on again. If I trigger another resolution change most of the times it comes back to life, but it's very annoying because when kernel loads (power on) and video driver loads it changes from BIOS video resolution to full HD and some of the times the LCD shuts down (and without an HDMI monitor my only option is to power off and power on again). I keep a HDMI monitor connected and HDMI never fails. I tried with Windows and the catalyst driver does not fail. I can change resolution hundreds of times in windows and it never fails. I also noticed that on windows, when I change resolution, both LCD and HDMI go off, and then LCD (LVDS) turns on first and then HDMI turns on. On Linux its different, both go off on a resolution change but LCD (LVDS) always turns on AFTER HDMI.. and sometimes it does not turn on at all. Backlight is off when it fails, but I tried illuminating the LCD panel and there are no pixels, so its does not look like a backlight issue.
It is using a CH7511B to convert from eDP to LVDS.
Here is dmesg (without drm.debug=0xe) and Xorg.log.0 (which shows different attempts to change resolution, on the one before the last one it failed, but I don't see any clear indication, it just did not turn off, but software wise all looks correct).
Hardware description:
- CPU: AMD A8 3500M
- GPU: Radeon HD 6620G
- System Memory: 4GB
- Display(s): 2 displays 1920x1080
- Type of Display Connection: eDP --> LVDS (CH7511B) and HDMI
System information:
- Distro name and Version: Ubuntu 21.04 (also ubuntu 20.04, tinycore several versions)
- Kernel version: 5.11.0-16 (ubuntu)
- Custom kernel: <TODO: e.g., Kernel from drm-misc-next, commit: "Message">
- AMD package version: <TODO: e.g., "20.02" or "No package">
How to reproduce the issue:
The issue happens during boot, when the BIOS hands off to the kernel and the kernel loads the video driver it changes from BIOS resolution (like 800x600, not sure) to 1920x1080. On some boots, the LVDS LCD does not turn back on. Most of the times work. If it fails and I have a HDMI monitor and I run (after X starts) xrandr --fb 1920x1079 (I know its not 1920x1080 but this 1079 forces a resolution change) it usually comes back to live.
To reproduce I just keep running the xrandr resolution change and after a few tries it fails. So that way I can sort of trigger the problem on demand
Attached files:
- Dmesg log
- Xorg log