launching Xorg fails with the r128 driver. It seems that newer versions of the r128 xorg driver need to allocate more memory than the video card actually have (in my case, on a Powerbook G3 Pismo, an ATI RAGE with 8MB). Setting 'Option "NoAccel" "True"' in xorg.conf did not helped. Reducing the color depth 'DefaultDepth 16' kind of helped. The X server starts but it only displays garbage (last video buffer from the tty slowly becoming white).
The amount of memory it tries to allocate by default is usually higher, yes. This is because the modes come from RandR which has more capable cards in mind. However, it should be easy to pick a smaller resolution in xorg.conf just like you picked a smaller color depth. Hopefully that can get it back to the same memory consumption that it had before.
I just discovered this approx. same issue on my Powermac 3,1 while running U-MATE Xenial for PPC when I added the "proper" r128 video driver. After doing that I can see some log files and comments while the system boots, but arriving at what should be the splash . . . is now a blackish screen. With the original install a few months back I think the installer picked "fbdevhw" as the driver and generally the display was good resolution. However, the log in screen had issues with low resolution background image, so I filed a bug report launchpad #1541082. A few days ago someone actually tried to help troubleshoot the problem and suggested that for my video card, the ATI Rage 128 Pro card, the driver should be "r128" . . . unfortunately after I installed that driver "X" was gone. I am able to get to a TTY to do stuff, but, as of today I haven't had a chance to get an xorg.conf file set up to see if I can change the driver to something else . . . just reporting the problem that occurred with r128. Link to LP bug: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1541082 F
An xorg.conf is required to use this driver, especially with powerpc. See comment 7 of bug 91421. Hopefully it will work if you make Section "Screen" and SubSection "Display" that lists reasonable resolutions.
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