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  • Rafael J. Wysocki's avatar
    PM / Domains: Add preliminary support for cpuidle, v2 · cbc9ef02
    Rafael J. Wysocki authored
    On some systems there are CPU cores located in the same power
    domains as I/O devices.  Then, power can only be removed from the
    domain if all I/O devices in it are not in use and the CPU core
    is idle.  Add preliminary support for that to the generic PM domains
    First, the platform is expected to provide a cpuidle driver with one
    extra state designated for use with the generic PM domains code.
    This state should be initially disabled and its exit_latency value
    should be set to whatever time is needed to bring up the CPU core
    itself after restoring power to it, not including the domain's
    power on latency.  Its .enter() callback should point to a procedure
    that will remove power from the domain containing the CPU core at
    the end of the CPU power transition.
    The remaining characteristics of the extra cpuidle state, referred to
    as the "domain" cpuidle state below, (e.g. power usage, target
    residency) should be populated in accordance with the properties of
    the hardware.
    Next, the platform should execute genpd_attach_cpuidle() on the PM
    domain containing the CPU core.  That will cause the generic PM
    domains framework to treat that domain in a special way such that:
     * When all devices in the domain have been suspended and it is about
       to be turned off, the states of the devices will be saved, but
       power will not be removed from the domain.  Instead, the "domain"
       cpuidle state will be enabled so that power can be removed from
       the domain when the CPU core is idle and the state has been chosen
       as the target by the cpuidle governor.
     * When the first I/O device in the domain is resumed and
       __pm_genpd_poweron(() is called for the first time after
       power has been removed from the domain, the "domain" cpuidle
       state will be disabled to avoid subsequent surprise power removals
       via cpuidle.
    The effective exit_latency value of the "domain" cpuidle state
    depends on the time needed to bring up the CPU core itself after
    restoring power to it as well as on the power on latency of the
    domain containing the CPU core.  Thus the "domain" cpuidle state's
    exit_latency has to be recomputed every time the domain's power on
    latency is updated, which may happen every time power is restored
    to the domain, if the measured power on latency is greater than
    the latency stored in the corresponding generic_pm_domain structure.
    Signed-off-by: default avatarRafael J. Wysocki <>
    Reviewed-by: default avatarKevin Hilman <>