Support for AMD Llano APU

Question

I recently built a new computer to serve as a fileserver and media station. As such, it has tons of hard drives, and just barely enough graphics to play HD video. The important aspects (as far as I know) are as follows:
Processor and graphics: AMD A4-3400 Llano APU
OS: plain-old vanilla Arch on kernel 3.3.7-1, x86_64 (all packages up to date as well)
Bootloader: syslinux
Desktop: SLIM into Xmonad
Here's the problem:
During initial setup, I kept running into a problem where, during the boot process, as soon as it hit the point where it started loading X, my monitor would just go black and everything would be completely uninteractable. After some digging around, I figured out that I needed to add "nomodeset" to my kernel line. As such, my syslinux.cfg file has an entry as follows:
MENU LABEL Arch Linux
LINUX ../vmlinuz-linx
APPEND root=/dev/disk/by-uuid/<snip> ro
INITRD ../initramfs-linux.img nomodeset
This works. So far, so good. However, it does have a problem -- I'm not able to correctly autodetect the resolution/aspect ratio of the monitor the computer is connected to. As such, I get rather terrible stretching and squishing whenever I hook up to, say, a 16:9 monitor. To rectify this, I tried using xrandr to manually add and set the proper resolution (as described at https://wiki.archlinux.org/index.php/Xr … solutions). However, every time I try to do this I get some errors:
> xrandr --newmode "1280x1024_60.00"  109.00  1280 1368 1496 1712  1024 1027 1034 1063 -hsync +vsync
xrandr: Failed to get size of gamma for output default
> xrandr --addmode default "1280x1024_60.00"
xrandr: Failed to get size of gamma for output default
> xrandr --output default --mode "1280x1024_60.00"
xrandr: Failed to get size of gamma for output default
xrandr: Configure crtc 0 failed
Again, after some googling and digging I found this page (https://wiki.archlinux.org/index.php/ATI) which explains all about the drivers I should be using. My first thought was that I didn't have the right drivers installed -- wrong, I've got xf86-video-ati. I followed all the instructions on that page regarding setting up KMS properly... and one of the instructions says to make sure you remove "nomodeset" from the kernel line. Well, fine, I did that. And now I'm back where I started.
TL;DR: I have been unable to find any instructions that will let me both a) have anything display at all (what I was getting via nomodeset) and b) properly load and take advantage of the graphics drivers (what I assume the ATI instructions would have let me do).
Any advice, tips, or other places to look?
Thanks,
Phas

Answer 1

Here is the long and short of it.
This bug is in the kernel.
The bug is not fixed in 3.4
The bug may be fixed in 3.5 but it is not listed in the drm pull list.  Apparently they fixed the bug around 5/27 and it may or may not have made it into the final pull list.
This bug concerns the D-sub port.  If you do not use the D-sub connection you can disable it with a kernel opiton.  This should fix the problem.
If you are using the D-sub port then the bug should be "fixed" in the current kernel if you have no other video conections.  If you are using more then 1 video connection then you are currently screwed.  The D-sub port currently does not work with other active video ports in linux or at least not the framebuffer.  X does work over both D-sub and DVI/HDMI at the same time.
To disable the D-sub port look in /sys/class/drm/card0 for the name of the D-sub port.  It should be card0-VGA-1.  Add the line video=VGA-1:d to the append line in syslinux.cfg.
This is what I have been able to piece together from various bug reports/workarounds on the net, and my own experience with the bug.  I stronly suggest you add a line to the append line that either enables (:e) or disables(:d) the VGA port no matter what you do since this greatly speeds up the kernel boot time.  Mine went from 6.5 seconds to 1.5 seconds when I did this.