Many bits in the CMD register are supposed to be strictly read-only.
We should not be deleting them on every write.
As a side-effect: pay explicit attention to when a guest marks off
the FIS Receive or Start bits, and disable the status bits ourselves,
instead of letting them implicitly fall off.
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1426283454-15590-3-git-send-email-jsnow@redhat.com
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