[LinuxBIOS] How to parameterise SDRAM init on Geode GX1?

[Juergen Beisert]

Hi,

the routine sdram_init() in LinuxBIOSv2/src/northbridge/amd/gx1/raminit.c does 
a very slow SDRAM timing setup. On a 266MHz CPU the SDRAM will run at 76MHz 
with a CAS latency of 3. You can't run a SXGA reolution with 64k colours on 
such a slow system. On my mainboard I can't read the EEPROM on the SODIMM, as 
I have no schematics and do not know if the manufacturer has routed some of 
the GPIOs as a I2C bus to this EEPROM. But I know the SDRAM chips on the 
SODIMM in my system!
Is there a "regular" way in LinuxBIOS to parameterise the SDRAM setup with 
some predefined macros in a (maybe) headerfile, so each GX1 based mainboard 
could overwrite the slowest timing with its own faster timing (if the 
programmer knows his SDRAM timings). In my case I can run some of my SODIMMs 
at 120MHz@CL2, some other with 100MHz@CL2 (300MHz Geode GX1).

Maybe the trick with a searchpath for headerfiles. There will be a generic 
file with the slowest timing in a directory at the end of the searchpath and 
the prgrammer can provide his own timing headerfile that would be found first 
if present?

Juergen