The USB4 Inter-Domain Service specification defines a protocol that can
be used to establish lane bonding between two USB4 domains (hosts). So
far we have not implemented it because the host controller DMA was not
fast enough to be able to go over 20 Gbits/s even if lanes were bonded.
However, starting from Intel Alder Lake CPUs the DMA can go over
20 Gbits/s so now it makes more sense to add this support to the driver.
Because both ends need to negotiate the bonding we add a simple state
machine that tracks the connection state and does the necessary steps
described by the USB4 Inter-Domain Service specification. We only
establish lane bonding when both sides of the link support it. Otherwise
we default to use the single lane. Also this is only done when software
connection manager is used. On systems with firmware based connection
manager, it handles the high-speed tunneling so bonding lanes is
specific to the implementation (Intel firmware based connection manager
does not support lane bonding).
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
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