Have you gone over this?:
Will coreboot work on my machine?
See the Supported Motherboards page for which mainboards are supported, and also the list of Supported Chipsets and Devices. See the Products page for a list of vendors selling products running coreboot.
If the above sources don't help, please send the following to the mailing list:
Step 1: A very brief description of your system: board vendor, board name, CPU, northbridge, southbridge, and optionally other important details.
Step 2: Linux "lspci -tvnn" output for your system, generated by booting Linux via the original BIOS and runnning lspci.
Step 3: Super I/O chip on the mainboard (report the model numbers on the actual chip, for example "Winbond W83627HF" and/or run "superiotool -dV").
Step 4: Type of BIOS device (see the question "How do I identify the BIOS chip on my mainboard?" below). Please send us the output of "flashrom -V"
Step 5: URL to the mainboard specifications page (optional).
Step 6: Any other relevant information you can provide.
If you can't do step 1 above, please describe (as best you can) the specific CPU chip and the chipset used on the mainboard.
Usually in less than a day, someone will respond on the coreboot mailing list saying your mainboard is supported in the main coreboot source tree, it is currently in development, it is not yet supported or the manufacturer will not release information needed to provide coreboot support. In the latter case, please let the manufacturer know that you want coreboot support and his failure to release chipset information is making that very difficult.
You may want to follow the above instructions and post to the coreboot mailing list.
Also, both the US2H(rev. 1.0 & 2.0) and the S2H (rev 1.0, 1.1, 2.x) have multiple revisions which seem to use different BIOS versions.