[Bug 1791312] Re: ubuntu 18.04 flickering screen with Radeon X1600

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https://bugs.launchpad.net/bugs/1791312

Title:
ubuntu 18.04 flickering screen with Radeon X1600

Status in Linux:
Fix Released
Status in linux package in Ubuntu:
Confirmed
Status in linux source package in Bionic:
Fix Released
Status in linux source package in Cosmic:
Fix Committed
Status in linux source package in Disco:
Fix Released

Bug description:
=== SRU Justification ===
[Impact]
Screen flickers when using radeon.ko.
It's a regression, it didn't happen on Trusty.

[Fix]
Quote the original commit log:
"Instead of the closest reference divider prefer the lowest".

[Test]
Affected user confirms it fixes the issue.

[Regression Potential]
Low. Only affect radeaon, and it's in upstream stable tree.

=== Original Bug Report ===
my laptop: HP Compaq nx9420
my grafic card:
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV530/M56-P [Mobility Radeon X1600] (prog-if 00 [VGA controller])

attachment:
the bug-apport-file

Description:
I start ubuntu 18.04 LTS (Kernel 4.15.0.33) in textmode;
-> as soon as the kernel-module radeon.ko is loaded the screen starts flickering
when starting the grafic-mode the flickering continues; so the screen is unusable.

when setting the option "radeon.modeset=0" (thus: not use radeon drivers) the screen does not flicker
but the resolution is limited to 1400x1050 (instead of natural 1680x1050)
so I can not use this as work-around

when using the old ubuntu 14.04.05 LTS (Kernel 3.13.0-157)
the screen is o.k. NO flickering in textmode, nice grafic, NO flickering
xrandr tells: 1680x1050 60.1

so I must stay on old ubuntu 14.04.05 ???

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