pc: port 92 reset requires a low->high transition
The PIIX datasheet says that "before another INIT pulse can be generated via [port 92h], [bit 0] must be written back to a zero. This bug is masked right now because a full reset will clear the value of port 92h. But once we implement soft reset correctly, the next attempt to enable the A20 line by setting bit 1 (and leaving the others untouched) will cause another reset. Reviewed-by: NAnthony Liguori <aliguori@us.ibm.com> Reviewed-by: NMichael S. Tsirkin <mst@redhat.com> Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
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