I previously worked on this, but abandoned the effort. I still have my R500.
ACPI is broken; thermal sensor reports overheating at boot, when there is no overheating. Faulty sensor readings.
Other things e.g. hda_verb, devicetree need fixing.
See: Motherboard porting guide in coreboot
Does not have GbE region, unlike other GM45 laptops. Generate descriptor without defined GbE region. The ich9gen util already supports this use-case (support was added for future work on R500).