Init them to defaults.
Make CONFIG_CNTL 8 bytes so unaligned read/write is easier.
Write changes to CONFIG_CNTL even if offset + size is > 4.
Log aperture change only if first byte (LSB) of CONFIG_CNTL is written. The driver might only write to the 2 most significant bytes which won't affect aperture size.
Offset and size are applied to the destination, not to source value, so we shouldn't use extract_bits when logging value.
Use ATI bitfield enums in switch statement.