Hi Alois,
I first want to say that I agree with kernel people that this is a BIOS issue.
Alois Schlögl wrote:
I'm wondering whether coreboot will work in my machine.
Not coreboot, but flashrom looks good.
Found chip "Winbond W25x80" (1024 KB) at physical address 0xfff00000.
The BIOS update you linked to in kernel bugzilla, http://us.sapphiretech.com/drivers/78SAPV09_20090522_4854.zip, contains a BIOS from May, with upgrades from AGESA (this is a BIOS library from AMD) 3.3.2.0 to 3.3.2.3. I don't know if this will fix the problem you are seeing.
You could update your BIOS using flashrom and the 78SAPV09.BIN file in that zip. Run flashrom -E to erase your flash chip and then flashrom -wv 78SAPV09.BIN to program and verify the new BIOS.
Ideally you should have a restore method before trying this. flashrom -E if it works will erase the flash chip completely. If you have a power outage at that point the system will not start again and the flash chip must be reprogrammed somewhere/somehow else, or the mainboard replaced.
//Peter