driver core: Handle cycles in device links created by fw_devlink

driver core: Handle cycles in device links created by fw_devlink

Sometimes, firmware can have cyclic dependencies between devices. But
one or more of those dependencies in the cycle are false dependencies
that don't affect the probing of the device.

fw_devlink can detect some of these false dependencies using logic. But
when it can't, we don't want to block probing of the devices in this
cyclic dependency.

So, instead of using normal device links for the devices in this cycle,
we need to switch to SYNC_STATE_ONLY device links between these devices.
This is so that sync_state() callback correctness is still maintained
while we allow these device to probe.

This is functionally similar to switching to fw_devlink=permissive just
for the devices in the cycle.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20201218031703.3053753-5-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>