(In QEMU, we call this the "select" register.)
My memory isn't good enough to memorize what these magic runes
do. Label them to prevent mixups from happening in the future.
Side note: I assume it's safe to always set 0xA0 even though ATA2 claims
these bits are reserved, because ATA3 immediately reinstated that these
bits should be always on. ATA4 and subsequent specs only claim that the
fields are obsolete, so I assume it's safe to leave these set and that
it should work with the widest array of guests.
Signed-off-by: John Snow <jsnow@redhat.com>
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