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SubjectRe: [v3, 1/2] powernv/powerpc:Save/Restore additional SPRs for stop4 cpuidle
On Fri, 2017-07-21 at 10:41:37 UTC, "Gautham R. Shenoy" wrote:
> From: "Gautham R. Shenoy" <>
> The stop4 idle state on POWER9 is a deep idle state which loses
> hypervisor resources, but whose latency is low enough that it can be
> exposed via cpuidle.
> Until now, the deep idle states which lose hypervisor resources (eg:
> winkle) were only exposed via CPU-Hotplug. Hence currently on wakeup
> from such states, barring a few SPRs which need to be restored to
> their older value, rest of the SPRS are reinitialized to their values
> corresponding to that at boot time.
> When stop4 is used in the context of cpuidle, we want these additional
> SPRs to be restored to their older value, to ensure that the context
> on the CPU coming back from idle is same as it was before going idle.
> In this patch, we define a SPR save area in PACA (since we have used
> up the volatile register space in the stack) and on POWER9, we restore
> SPRN_MMCR2 to the values they had before entering stop.
> Signed-off-by: Gautham R. Shenoy <>
> Reviewed-by: Nicholas Piggin <>

Series applied to powerpc next, thanks.


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