• Gautham R. Shenoy's avatar
    powerpc/powernv: Save/Restore additional SPRs for stop4 cpuidle · e1c1cfed
    Gautham R. Shenoy authored
    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_PID, SPRN_LDBAR, SPRN_FSCR, SPRN_HFSCR, SPRN_MMCRA, SPRN_MMCR1,
    SPRN_MMCR2 to the values they had before entering stop.
    Signed-off-by: default avatarGautham R. Shenoy <ego@linux.vnet.ibm.com>
    Reviewed-by: default avatarNicholas Piggin <npiggin@gmail.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    e1c1cfed
idle_book3s.S 23.9 KB