Dtyjlui

I have screen flickering problem when I'm connecting my laptop to my TV. I found that when I change the refresh rate from 60Hz to 59Hz this problem disappear.

Within Xorg (as I know 18.04 uses it by default) you can change the refresh rate by the help of xrandr:

0. First you must find the video output name to which you should assing the new mode. Just type xrandr and investigate which one is it. In my case this is HDMI-1.

1. Generate new modeline using cvt:

$ cvt 1920 1080 59

# 1920x1080 58.94 Hz (CVT) hsync: 66.02 kHz; pclk: 169.00 MHz

Modeline "1920x1080_59.00"  169.00  1920 2040 2240 2560  1080 1083 1088 1120 -hsync +vsync

• 
  1920 and 1080 are the horizontal and vertical resolution's values.


• 
  59 is the value of the refresh rate.

2. Create the new mode:

xrandr --newmode 1920x1080_59.00  169.00  1920 2040 2240 2560  1080 1083 1088 1120 -hsync +vsync

3. Assign the new mode to the video output:

xrandr --addmode HDMI-1 1920x1080_59.00

4. Activate the new mode:

xrandr --output HDMI-1 --mode 1920x1080_59.00

If the above works and the problem disappear, you should find a proper way to add and set this mode at the system startup. Here are few references about that:

• How can I make xrandr customization permanent?


• Adding newmode with Xrandr - "800x480_60.00"


• start up command


• Differences how to run scripts at startup

I've no answer here, but some observation and confirmation of problem. If someone finds this text: please stick to ubuntu 17.10 if you have radeon rx 580 (may be 480 and vegas)

Got myself to very same situation with 18.04 (upgrade, then fresh install). Amd rx 580 here, kernel 4.15.0-20.

What did not help:

• fresh install after upgrade


• 
  oibaf drivers


• 
  M-Bab custom kernel


• 
  4.17-rc3 kernel from main line ppa.


• amdgpu.dc=1 as boot parameter (/etc/default/grub)

Update:
Apparently older kernel works. I've been tinkering with other distibutions and found that kernel 4.15.14 works for rx 580, you may want to try it from mainline ppa.

Turn off the automatic brightness control to fix this.

I faced a similar problem,I wasn't able to log in with the graphical mode at all, I solved it by :

1- enter to tty mode (ctrl+alt+f5, en my case)

2- adding open grafic Drivers (https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers):

      sudo add-apt-repository ppa:oibaf/graphics-drivers

      sudo apt-get update

3- reboot

4- enter into tty mode again

5-

 sudo apt update && sudo apt full-upgrade

Just got 4.19-rc1 kernel installed and flickering is completly gone, no need to restart PC no other magic - it works out of the box.

I'm using Arch now, but believe ubuntu's mainline kernel going to provide same experience. http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.19-rc1/

I had the same issue with my RX580 (Kubuntu 18.04, Plasma 5). The flickering only started when the GPU got higher load (playing the Witcher 3 in my case).

First I installed the 4.19 kernel (which has amdgpu.dc=1 by default).

That alone didn't seem to help but maybe contributes to the fix.

Than, I set the screen refresh rate to 59.xx hz with the KDE monitor settings GUI.

After this, the problem seems to be fixed.

In my case the flickering started when I manually switched screen resolution with xrandr (without an explicit refresh rate setting), so maybe the refresh rate was misconfigured by those commands and only the refresh rate needed to be fixed.