PM / core: Add LEAVE_SUSPENDED driver flag

Define and document a new driver flag, DPM_FLAG_LEAVE_SUSPENDED, to
instruct the PM core and middle-layer (bus type, PM domain, etc.)
code that it is desirable to leave the device in runtime suspend
after system-wide transitions to the working state (for example,
the device may be slow to resume and it may be better to avoid
resuming it right away).

Generally, the middle-layer code involved in the handling of the
device is expected to indicate to the PM core whether or not the
device may be left in suspend with the help of the device's
power.may_skip_resume status bit.  That has to happen in the "noirq"
phase of the preceding system suspend (or analogous) transition.
The middle layer is then responsible for handling the device as
appropriate in its "noirq" resume callback which is executed
regardless of whether or not the device may be left suspended, but
the other resume callbacks (except for ->complete) will be skipped
automatically by the core if the device really can be left in
suspend.

The additional power.must_resume status bit introduced for the
implementation of this mechanisn is used internally by the PM core
to track the requirement to resume the device (which may depend on
its children etc).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

3 files changed, 105 insertions, 11 deletions

diff --git a/Documentation/driver-api/pm/devices.rst b/Documentation/driver-api/pm/devices.rst
index 53c1b0b06da5..b0fe63c91f8d 100644
--- a/Documentation/driver-api/pm/devices.rst
+++ b/Documentation/driver-api/pm/devices.rst
@@ -788,6 +788,29 @@ 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
+[Refer to that document for more information regarding this particular issue as
 well as for information on the device runtime power management framework in
-general.
+general.]
+
+However, it often is desirable to leave devices in suspend after system
+transitions to the working state, especially if those devices had been in
+runtime suspend before the preceding system-wide suspend (or analogous)
+transition.  Device drivers can use the ``DPM_FLAG_LEAVE_SUSPENDED`` flag to
+indicate to the PM core (and middle-layer code) that they prefer the specific
+devices handled by them to be left suspended and they have no problems with
+skipping their system-wide resume callbacks for this reason.  Whether or not the
+devices will actually be left in suspend may depend on their state before the
+given system suspend-resume cycle and on the type of the system transition under
+way.  In particular, devices are not left suspended if that transition is a
+restore from hibernation, as device states are not guaranteed to be reflected
+by the information stored in the hibernation image in that case.
+
+The middle-layer code involved in the handling of the device is expected to
+indicate to the PM core if the device may be left in suspend by setting its
+:c:member:`power.may_skip_resume` status bit which is checked by the PM core
+during the "noirq" phase of the preceding system-wide suspend (or analogous)
+transition.  The middle layer is then responsible for handling the device as
+appropriate in its "noirq" resume callback, which is executed regardless of
+whether or not the device is left suspended, but the other resume callbacks
+(except for ``->complete``) will be skipped automatically by the PM core if the
+device really can be left in suspend.
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index db2f04415927..73ec6796d9e1 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -526,6 +526,18 @@ static void dpm_watchdog_clear(struct dpm_watchdog *wd)
 /*------------------------- Resume routines -------------------------*/
 
 /**
+ * dev_pm_may_skip_resume - System-wide device resume optimization check.
+ * @dev: Target device.
+ *
+ * Checks whether or not the device may be left in suspend after a system-wide
+ * transition to the working state.
+ */
+bool dev_pm_may_skip_resume(struct device *dev)
+{
+        return !dev->power.must_resume && pm_transition.event != PM_EVENT_RESTORE;
+}
+
+/**
  * device_resume_noirq - Execute a "noirq resume" callback for given device.
  * @dev: Device to handle.
  * @state: PM transition of the system being carried out.
@@ -573,6 +585,19 @@ static int device_resume_noirq(struct device *dev, pm_message_t state, bool asyn
         error = dpm_run_callback(callback, dev, state, info);
         dev->power.is_noirq_suspended = false;
 
+        if (dev_pm_may_skip_resume(dev)) {
+                /*
+                 * The device is going to be left in suspend, but it might not
+                 * have been in runtime suspend before the system suspended, so
+                 * its runtime PM status needs to be updated to avoid confusing
+                 * the runtime PM framework when runtime PM is enabled for the
+                 * device again.
+                 */
+                pm_runtime_set_suspended(dev);
+                dev->power.is_late_suspended = false;
+                dev->power.is_suspended = false;
+        }
+
  Out:
         complete_all(&dev->power.completion);
         TRACE_RESUME(error);
@@ -1074,6 +1099,22 @@ static pm_message_t resume_event(pm_message_t sleep_state)
         return PMSG_ON;
 }
 
+static void dpm_superior_set_must_resume(struct device *dev)
+{
+        struct device_link *link;
+        int idx;
+
+        if (dev->parent)
+                dev->parent->power.must_resume = true;
+
+        idx = device_links_read_lock();
+
+        list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
+                link->supplier->power.must_resume = true;
+
+        device_links_read_unlock(idx);
+}
+
 /**
  * __device_suspend_noirq - Execute a "noirq suspend" callback for given device.
  * @dev: Device to handle.
@@ -1125,10 +1166,28 @@ static int __device_suspend_noirq(struct device *dev, pm_message_t state, bool a
         }
 
         error = dpm_run_callback(callback, dev, state, info);
-        if (!error)
-                dev->power.is_noirq_suspended = true;
-        else
+        if (error) {
                 async_error = error;
+                goto Complete;
+        }
+
+        dev->power.is_noirq_suspended = true;
+
+        if (dev_pm_test_driver_flags(dev, DPM_FLAG_LEAVE_SUSPENDED)) {
+                /*
+                 * The only safe strategy here is to require that if the device
+                 * may not be left in suspend, resume callbacks must be invoked
+                 * for it.
+                 */
+                dev->power.must_resume = dev->power.must_resume ||
+                                        !dev->power.may_skip_resume ||
+                                        atomic_read(&dev->power.usage_count) > 1;
+        } else {
+                dev->power.must_resume = true;
+        }
+
+        if (dev->power.must_resume)
+                dpm_superior_set_must_resume(dev);
 
 Complete:
         complete_all(&dev->power.completion);
@@ -1485,6 +1544,9 @@ static int __device_suspend(struct device *dev, pm_message_t state, bool async)
                 dev->power.direct_complete = false;
         }
 
+        dev->power.may_skip_resume = false;
+        dev->power.must_resume = false;
+
         dpm_watchdog_set(&wd, dev);
         device_lock(dev);
 
@@ -1650,8 +1712,9 @@ static int device_prepare(struct device *dev, pm_message_t state)
         if (dev->power.syscore)
                 return 0;
 
-        WARN_ON(dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) &&
-                !pm_runtime_enabled(dev));
+        WARN_ON(!pm_runtime_enabled(dev) &&
+                dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND |
+                                              DPM_FLAG_LEAVE_SUSPENDED));
 
         /*
          * If a device's parent goes into runtime suspend at the wrong time,
diff --git a/include/linux/pm.h b/include/linux/pm.h
index 65d39115f06d..b5a40b713e9e 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -556,9 +556,10 @@ struct pm_subsys_data {
  * These flags can be set by device drivers at the probe time.  They need not be
  * cleared by the drivers as the driver core will take care of that.
  *
- * NEVER_SKIP: Do not skip system suspend/resume callbacks for the device.
+ * NEVER_SKIP: Do not skip all 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.
+ * LEAVE_SUSPENDED: Avoid resuming the device during system resume if possible.
  *
  * 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
@@ -572,10 +573,14 @@ struct pm_subsys_data {
  * 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.
+ *
+ * Setting LEAVE_SUSPENDED informs the PM core and middle-layer code that the
+ * driver prefers the device to be left in suspend after system resume.
  */
-#define DPM_FLAG_NEVER_SKIP     BIT(0)
-#define DPM_FLAG_SMART_PREPARE  BIT(1)
-#define DPM_FLAG_SMART_SUSPEND  BIT(2)
+#define DPM_FLAG_NEVER_SKIP             BIT(0)
+#define DPM_FLAG_SMART_PREPARE          BIT(1)
+#define DPM_FLAG_SMART_SUSPEND          BIT(2)
+#define DPM_FLAG_LEAVE_SUSPENDED        BIT(3)
 
 struct dev_pm_info {
         pm_message_t            power_state;
@@ -597,6 +602,8 @@ struct dev_pm_info {
         bool                    wakeup_path:1;
         bool                    syscore:1;
         bool                    no_pm_callbacks:1;      /* Owned by the PM core */
+        unsigned int            must_resume:1;  /* Owned by the PM core */
+        unsigned int            may_skip_resume:1;      /* Set by subsystems */
 #else
         unsigned int            should_wakeup:1;
 #endif
@@ -765,6 +772,7 @@ extern int pm_generic_poweroff_late(struct device *dev);
 extern int pm_generic_poweroff(struct device *dev);
 extern void pm_generic_complete(struct device *dev);
 
+extern bool dev_pm_may_skip_resume(struct device *dev);
 extern bool dev_pm_smart_suspend_and_suspended(struct device *dev);
 
 #else /* !CONFIG_PM_SLEEP */