Created attachment 144837 [details]
dmesg output after blacklisting radeon, then enabling it after boot

I have a laptop with a Radeon Mobility 3670. With KMS disabled I can boot normally; however, otherwise it typically locks hard as soon as modesetting happens, with an odd effect where the screen gradually fades to being nearly completely white. (I can provide video if for some reason this would help).

However, on occasion (rarely) it will flicker for a second, successfully switch modes, spit out "Timeout setting UVD clocks", and then carry on correctly.

Given that this happens very early in the boot, and hard locks the system, I've taken to blacklisting radeon in my boot parameters, then doing a "sudo modprobe radeon" after logging in and crossing my fingers. Attached is dmesg output from such a case - note the delay between lines 918 and 919 as boot finished, I logged in, and then ran modprobe. Lines 950-955 show the errors that get echoed as the system then successfully switches modes.

(blacklisting until after boot isn't the only way to get it working - it just happens to give me more of a sense of control than repeatedly power-cycling and hoping the system boots normally.)

The closest example I could find on search was 16389 - however none of the workarounds there help, and when the screen fades the machine is subsequently completely unreponsive.

Debian 10 buster, 1:19.0.1-1