powernv CPUs have a set of control registers that can stop, start, and do other things to control a thread's execution. Using this interface to stop a thread puts it into a particular state that can be queried, and is distinguishable from other things that might stop the CPU (e.g., going idle, or being debugged via gdb, or stopped by the monitor). Add a new flag that can speficially distinguish this state where it is stopped with control registers. This solves some hangs when rebooting powernv machines when skiboot is modified to allow QEMU to use the CPU control facility (that uses controls to bring all secondaries to a known state). Fixes: c8891955086 ("ppc/pnv: Implement POWER10 PC xscom registers for direct controls") Reviewed-by: Glenn Miles <milesg@linux.ibm.com> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>