int ide_build_dmatable (ide_drive_t * drive, struct request * rq);
ide_build_dmatable prepares a dma request. We map the command to get the pci bus addresses of the buffers and then build up the PRD table that the IDE layer wants to be fed. The code knows about the 64K wrap bug in the CS5530.
Returns 0 if all went okay, returns 1 otherwise. May also be invoked from trm290.c