The following commit was intended to fix problems with specific AHCI
controller(s) that would become bricks if the AHCI specification was not
followed strictly (that is, if ahci_start_engine() was called while the
controller was in the wrong state):

    commit 7faa33da
    ahci: start engine only during soft/hard resets

However, some devices currently have issues with that fix, so we must
implement a flag that delays the ahci_start_engine() call only for specific
controllers.

This commit simply introduces the flag, without enabling it in any driver.

Note that even when AHCI_HFLAG_DELAY_ENGINE is not enabled, this patch does
not constitue a full revert to commit 7faa33da; there is still a change in
behavior to the ahci_port_suspend() failure path.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Cc: stable@kernel.org