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Diffstat (limited to 'Documentation/driver-api')
-rw-r--r-- | Documentation/driver-api/pm/devices.rst | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/driver-api/pm/devices.rst b/Documentation/driver-api/pm/devices.rst index 8add5b302a89..574dadd06dec 100644 --- a/Documentation/driver-api/pm/devices.rst +++ b/Documentation/driver-api/pm/devices.rst @@ -766,6 +766,26 @@ the state of devices (possibly except for resuming them from runtime suspend) from their ``->prepare`` and ``->suspend`` callbacks (or equivalent) *before* invoking device drivers' ``->suspend`` callbacks (or equivalent). +Some bus types and PM domains have a policy to resume all devices from runtime +suspend upfront in their ``->suspend`` callbacks, but that may not be really +necessary if the driver of the device can cope with runtime-suspended devices. +The driver can indicate that by setting ``DPM_FLAG_SMART_SUSPEND`` in +:c:member:`power.driver_flags` at the probe time, by passing it to the +:c:func:`dev_pm_set_driver_flags` helper. That also may cause middle-layer code +(bus types, PM domains etc.) to skip the ``->suspend_late`` and +``->suspend_noirq`` callbacks provided by the driver if the device remains in +runtime suspend at the beginning of the ``suspend_late`` phase of system-wide +suspend (or in the ``poweroff_late`` phase of hibernation), when runtime PM +has been disabled for it, under the assumption that its state should not change +after that point until the system-wide transition is over. If that happens, the +driver's system-wide resume callbacks, if present, may still be invoked during +the subsequent system-wide resume transition and the device's runtime power +management status may be set to "active" before enabling runtime PM for it, +so the driver must be prepared to cope with the invocation of its system-wide +resume callbacks back-to-back with its ``->runtime_suspend`` one (without the +intervening ``->runtime_resume`` and so on) and the final state of the device +must reflect the "active" status for runtime PM in that case. + During system-wide resume from a sleep state it's easiest to put devices into the full-power state, as explained in :file:`Documentation/power/runtime_pm.txt`. Refer to that document for more information regarding this particular issue as |