POWER8 (ISA v2.07S) introduced the doorbell facility, the msgsnd
instruction behaved mostly like msgsndp, it was addressed by TIR
and could only send interrupts between threads on the core.
ISA v3.0 changed msgsnd to be addressed by PIR and can interrupt
any thread in the system.
msgsnd only implements the v3.0 semantics, which can make
multi-threaded POWER8 hang when booting Linux (due to IPIs
failing). This change adds v2.07 semantics.
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
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