These chipsets don't seem to have a full AGP GART, (and in at least
two reports I've had, are used in systems that don't even have an
AGP slot).
Print something more informative than..
                                                                                           
  agpgart: unable to determine aperture size.
  agpgart: agp_backend_initialize() failed.
  agpgart-serverworks: probe of 0000:00:00.0 failed with error -22
  agpgart: Maximum main memory to use for agp memory: 941M
  agpgart: unable to determine aperture size.
  agpgart: agp_backend_initialize() failed.
  agpgart-serverworks: probe of 0000:00:00.1 failed with error -22
  agpgart: Unsupported Serverworks chipset (device id: 0006)
  agpgart: Unsupported Serverworks chipset (device id: 0006)