RX580: screen turns black or flickers until forced reconfiguration

Submitted by num..@..dex.ru

Assigned to Default DRI bug account

Link to original bug (#110217)

Description

Created attachment 143754
dmesg output

I have a Radeon RX560 and VGA monitor (with broken EDID) connected via a cheap HDMI-to-VGA converter (with its own broken EDID).

The system starts up normally. During boot up, it should change display resolution as specified in the kernel command line (video=1280x1024-32@75, monitor native). Screen turns black instead, and resolution remains unchanged. But after I plug HDMI out and in, the monitor gets new resolution and shows console login prompt, as expected. (X isn’t configured to start at bootup).

Then, when I startx, it chooses the same resolution but wrong frequency (85 Hz, too much for my monitor). That’s probably due to converter supplying the EDID. After I run xrandr --rate 75, it switches to the correct mode.

I wouldn’t even mention such small nuisance, but if I specify exactly the same mode (as reported by xrandr --verbose) explicitly (as a Modeline), it works but flickers, despite the TearFree option enabled. Moreover, when the monitor is turned off and then on, it wakes up in the same mode but flickers. Changing mode back and forth (xrandr --output HDMI-A-0 --preferred ; xrandr --rate 75) helps.

I usually have compton running. Without it, flicker is tolerable but still present.

OS: Arch Linux
Kernel: Linux 5.0.1-arch1-1-ARCH
X driver: xf86-video-amdgpu 19.0.0-1

Attachment 143754, "dmesg output":
kern.log