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  • Rafael J. Wysocki's avatar
    PM / QoS: Make it possible to expose PM QoS latency constraints · 85dc0b8a
    Rafael J. Wysocki authored
    A runtime suspend of a device (e.g. an MMC controller) belonging to
    a power domain or, in a more complicated scenario, a runtime suspend
    of another device in the same power domain, may cause power to be
    removed from the entire domain.  In that case, the amount of time
    necessary to runtime-resume the given device (e.g. the MMC
    controller) is often substantially greater than the time needed to
    run its driver's runtime resume callback.  That may hurt performance
    in some situations, because user data may need to wait for the
    device to become operational, so we should make it possible to
    prevent that from happening.
    For this reason, introduce a new sysfs attribute for devices,
    power/pm_qos_resume_latency_us, allowing user space to specify the
    upper bound of the time necessary to bring the (runtime-suspended)
    device up after the resume of it has been requested.  However, make
    that attribute appear only for the devices whose drivers declare
    support for it by calling the (new) dev_pm_qos_expose_latency_limit()
    helper function with the appropriate initial value of the attribute.
    Signed-off-by: default avatarRafael J. Wysocki <>
    Reviewed-by: default avatarKevin Hilman <>
    Reviewed-by: default avatarMark Brown <>
    Acked-by: default avatarLinus Walleij <>