#800524 xserver-xorg-video-radeon: Jessie / AMD A6 7400K / Radeon R5 - black screen instead of X started

Package:
xserver-xorg-video-radeon
Source:
xserver-xorg-video-ati
Description:
X.Org X server -- AMD/ATI Radeon display driver
Submitter:
Peter Tuharsky
Date:
2015-09-30 12:33:10 UTC
Severity:
important
#800524#5
Date:
2015-09-30 14:08:13 UTC
From:
To:
Dear Maintainer,

first, let me thank You for doing Your work for Debian.

I have Installed Debian Jessie. The first time, the X started in VESA regime
with all consequences (useless video, no 3D acceleration).
In order to get the VGA detected correctly, I have installed firmware-linux-nonfree.

Now after reboot, the X does not even start, there is just a black screen.
Xorg.log shows that RADEON driver (correct, I suppose) is being used now.
Fortunately, tty works so I'm reporting the bug from console.

I've been using AMD A4 7300 w/ Radeon 8470 before and everything works there like a charm.
I'm bitterly surprised that the "better" chip is barely functional in Debian.
What should I do?

Sincerely,
Peter