On Saturday 05 Mar 2016 00:10:23 Frank Steinmetzger wrote:
> Hello Fellows,
> 
> My PC had been running on Intel graphics for 1½ years. Finally, I got myself
> an AMD R7 370 today and installed it (together with a second set of 16 Gigs
> of RAM ^^).
> 
> I could use some help getting it working properly. Here is what I did:
> yesterday I enabled VIDEO_CARDS=radeon in make.conf and rebuilt world with
> --changed-use. I also reconfigured the kernel to build the Intel driver as
> a module and to include the radeon module.

I believe you need VIDEO_CARDS="radeon radeonsi".  Did you read this page?

https://wiki.gentoo.org/wiki/Radeon


> After installing the card, at first I only had a black screen and found out
> (thanks to #gentoo) that I needed a firmware blob. Once that was installed,
> I had a KMS-enabled VT on my AMD-connected monitor. Yay.
> 
> Now I'm stuck with a malfunctioning X (or more specifically, KDE, as it
> seems). I can run AwesomeWM just fine. But when I try to start KDE, I see
> the first of those fading-in progress icons and then the screen goes black.
> 
> I created a test account to have a clean setup of KDE. This starts KDE
> partially, only up to a desktop with an empty panel. There is no mouse
> cursor to move around and no reaction to shortcuts such as Alt+F2.
> 
> What else could I have missed in my migration from Intel to AMD? eselect
> opengl only shows the xorg-x11 option. I had to comment out a modeline which
> I set manually in xorg.conf.
> 
> See attached:
> - /etc/X11/xorg.conf.d/gfx.conf
> - /var/log/Xorg.0.log from running startx with .xinitrc containing startkde.
> You can see those three blocks of modelines at the end. At around or just
> before this point the screen goes dark.
> 
> Can anyone give me a nudge. Or maybe I should as in a KDE list.

Have you tried booting without a xorg.conf.d/gfx.conf file to see if it picks 
up the radeon drivers?
-- 
Regards,
Mick