powerpc/powernv/idle: Don't override default/deepest directly in kernel
Currently during idle-init on power9, if we don't find suitable stop states in the device tree that can be used as the default_stop/deepest_stop, we set stop0 (ESL=1,EC=1) as the default stop state psscr to be used by power9_idle and deepest stop state which is used by CPU-Hotplug. However, if the platform firmware has not configured or enabled a stop state, the kernel should not make any assumptions and fallback to a default choice. If the kernel uses a stop state that is not configured by the platform firmware, it may lead to further failures which should be avoided. In this patch, we modify the init code to ensure that the kernel uses only the stop states exposed by the firmware through the device tree. When a suitable default stop state isn't found, we disable ppc_md.power_save for power9. Similarly, when a suitable deepest_stop_state is not found in the device tree exported by the firmware, fall back to the default busy-wait loop in the CPU-Hotplug code. [Changelog written with inputs from svaidy@linux.vnet.ibm.com] Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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