Solved Issue moving from 1440p monitor to 2160P on rock5b using Jammy with Multimedia / setting boot resolution for 4k and login screen for desktop manager

[laconis]

Hello,

 

As stated recently I had setup a Rock5B with Jammy/Mutimedia and had issues with a 2160P / 3840 x 2160 screen.

 

Initially bootup would show a flickering screen.

Adding the custom resolutions via cvt/xrandr and setting line in boot env: "exrtaargs-video=HDMI-A-1:3840x2160@60"  fixed that issue

 

However the initial login screen and logout screen resulted in a vibrant flickering background .

This was on a Sceptre 50" TV and other perihperials would normally work fine. 

This took a while to figure out because I was confusing my active desktop provider and Gdm was being used:

 

https://askubuntu.com/questions/912052/how-do-i-change-gdm3-login-screen-resolution

 

However a similar issue could arrise if using lightdm and this goes over changing the lgoin screen resolution also:

 

https://askubuntu.com/questions/73804/wrong-login-screen-resolution

 

Posting this just in case anyone else is having this odd issue as it was quite an eyesore.. Thanks!