• Rafael J. Wysocki's avatar
    PM / core: Add NEVER_SKIP and SMART_PREPARE driver flags · 08810a41
    Rafael J. Wysocki authored
    The motivation for this change is to provide a way to work around
    a problem with the direct-complete mechanism used for avoiding
    system suspend/resume handling for devices in runtime suspend.
    
    The problem is that some middle layer code (the PCI bus type and
    the ACPI PM domain in particular) returns positive values from its
    system suspend ->prepare callbacks regardless of whether the driver's
    ->prepare returns a positive value or 0, which effectively prevents
    drivers from being able to control the direct-complete feature.
    Some drivers need that control, however, and the PCI bus type has
    grown its own flag to deal with this issue, but since it is not
    limited to PCI, it is better to address it by adding driver flags at
    the core level.
    
    To that end, add a driver_flags field to struct dev_pm_info for flags
    that can be set by device drivers at the probe time to inform the PM
    core and/or bus types, PM domains and so on on the capabilities and/or
    preferences of device drivers.  Also add two static inline helpers
    for setting that field and testing it against a given set of flags
    and make the driver core clear it automatically on driver remove
    and probe failures.
    
    Define and document two PM driver flags related to the direct-
    complete feature: NEVER_SKIP and SMART_PREPARE that can be used,
    respectively, to indicate to the PM core that the direct-complete
    mechanism should never be used for the device and to inform the
    middle layer code (bus types, PM domains etc) that it can only
    request the PM core to use the direct-complete mechanism for
    the device (by returning a positive value from its ->prepare
    callback) if it also has been requested by the driver.
    
    While at it, make the core check pm_runtime_suspended() when
    setting power.direct_complete so that it doesn't need to be
    checked by ->prepare callbacks.
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    Acked-by: default avatarBjorn Helgaas <bhelgaas@google.com>
    Reviewed-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
    08810a41
devices.rst 40.1 KB