Bug#443979: Works for me!
http://www.ebn-pos.com/products/Spec_SolidPPC50.php -> PPC508
after some struggle i finally found this bug report and my AMD GEODE LX800 booted fine with stock kernel via pxe with "video=lxfb:800×600-32@60".
A user reported that he failed to install even with custom "CONFIG_FIRMWARE_EDID=n"
kernel, but non-custom installer could work with "video=lxfb:1024×600-32@60"
He uses "Kojinsha SA5ST12A", it has AMD Geode LX800 chip.
I hope it would be help.
Hideki Yamane henrich @ debian.or.jp/iijmio-mail.jp