Radeondrm on R7 250 w 3840x2160

[Wolfgang Solfrank <Wolfgang%Solfrank.net@localhost>]

Hi,

recently I decided to get myself one of these 4k monitors for
more screen real estate.  Of course I also had to buy a new
graphics card, since the old one only supported up to 2560x1600.
I decided to try an R7 250 based card.

So I now had to get this to work somehow.  During the process
the following problems arose:

The in-tree X server is too old to recognize the new chip
(1002/683f).  So I had to switch to the modular-xorg-server.

The autoconfiguration (Xorg -configure) now finds the board,
but when creating the new xorg.conf, it ignores the PCI domain
in the BusID, i.e. the generated BusID reads "PCI:6:0:0" instead
of the required "PCI:6@1:0:0".

The driver for this chip doesn't work without DRMKMS.
Since I'm using a custom kernel for several reasons, I had
to add this option to my config, but don't forget to comment
out all the old drm drivers!  Booting this kernel does more or
less work, albeit it gets me a picture only about every other
try (see below).

The libdrm in pkgsrc doesn't have support for NetBSD DRMKMS,
so I had to bring the changes from the in-tree libdrm here.

Now X does start, can find the card and even displays something,
but only at a resolution of 1024x768.  That was not what we had
in mind with all this hassle.  Fortunately, this one was easy:  Just
create a modline in xorg.conf with the desired resolution (cvt
comes in handy for this: "cvt 3840 2160 60").

So now things work more or less as expected, except that I have
to boot several times to get to see something on the screen.
Similarly the picture doesn't recurr after the screensaver kicked
in, which can be cured by doing a  "xset dpms force off"
followed by a "xset dpms force on" from a remote box.

Maybe this helps people with similar configurations.

Ciao,
Wolfgang
-- 
Wolfgang%Solfrank.net@localhost				Wolfgang Solfrank