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
*
* NEVER_SKIP: Do not skip system suspend/resume callbacks for the device.
* SMART_PREPARE: Check the return value of the driver's ->prepare callback.
+ * SMART_SUSPEND: No need to resume the device from runtime suspend.
*
* Setting SMART_PREPARE instructs bus types and PM domains which may want
* system suspend/resume callbacks to be skipped for the device to return 0 from
* other words, the system suspend/resume callbacks can only be skipped for the
* device if its driver doesn't object against that). This flag has no effect
* if NEVER_SKIP is set.
+ *
+ * Setting SMART_SUSPEND instructs bus types and PM domains which may want to
+ * runtime resume the device upfront during system suspend that doing so is not
+ * necessary from the driver's perspective. It also may cause them to skip
+ * invocations of the ->suspend_late and ->suspend_noirq callbacks provided by
+ * the driver if they decide to leave the device in runtime suspend.
*/
#define DPM_FLAG_NEVER_SKIP BIT(0)
#define DPM_FLAG_SMART_PREPARE BIT(1)
+#define DPM_FLAG_SMART_SUSPEND BIT(2)
struct dev_pm_info {
pm_message_t power_state;