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-rw-r--r--Documentation/power/devices.txt67
-rw-r--r--Documentation/power/runtime_pm.txt31
2 files changed, 35 insertions, 63 deletions
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
index 88880839ece4..64565aac6e40 100644
--- a/Documentation/power/devices.txt
+++ b/Documentation/power/devices.txt
@@ -520,59 +520,20 @@ Support for power domains is provided through the pwr_domain field of struct
device. This field is a pointer to an object of type struct dev_power_domain,
defined in include/linux/pm.h, providing a set of power management callbacks
analogous to the subsystem-level and device driver callbacks that are executed
-for the given device during all power transitions, in addition to the respective
-subsystem-level callbacks. Specifically, the power domain "suspend" callbacks
-(i.e. ->runtime_suspend(), ->suspend(), ->freeze(), ->poweroff(), etc.) are
-executed after the analogous subsystem-level callbacks, while the power domain
-"resume" callbacks (i.e. ->runtime_resume(), ->resume(), ->thaw(), ->restore,
-etc.) are executed before the analogous subsystem-level callbacks. Error codes
-returned by the "suspend" and "resume" power domain callbacks are ignored.
-
-Power domain ->runtime_idle() callback is executed before the subsystem-level
-->runtime_idle() callback and the result returned by it is not ignored. Namely,
-if it returns error code, the subsystem-level ->runtime_idle() callback will not
-be called and the helper function rpm_idle() executing it will return error
-code. This mechanism is intended to help platforms where saving device state
-is a time consuming operation and should only be carried out if all devices
-in the power domain are idle, before turning off the shared power resource(s).
-Namely, the power domain ->runtime_idle() callback may return error code until
-the pm_runtime_idle() helper (or its asychronous version) has been called for
-all devices in the power domain (it is recommended that the returned error code
-be -EBUSY in those cases), preventing the subsystem-level ->runtime_idle()
-callback from being run prematurely.
-
-The support for device power domains is only relevant to platforms needing to
-use the same subsystem-level (e.g. platform bus type) and device driver power
-management callbacks in many different power domain configurations and wanting
-to avoid incorporating the support for power domains into the subsystem-level
-callbacks. The other platforms need not implement it or take it into account
-in any way.
-
-
-System Devices
---------------
-System devices (sysdevs) follow a slightly different API, which can be found in
-
- include/linux/sysdev.h
- drivers/base/sys.c
-
-System devices will be suspended with interrupts disabled, and after all other
-devices have been suspended. On resume, they will be resumed before any other
-devices, and also with interrupts disabled. These things occur in special
-"sysdev_driver" phases, which affect only system devices.
-
-Thus, after the suspend_noirq (or freeze_noirq or poweroff_noirq) phase, when
-the non-boot CPUs are all offline and IRQs are disabled on the remaining online
-CPU, then a sysdev_driver.suspend phase is carried out, and the system enters a
-sleep state (or a system image is created). During resume (or after the image
-has been created or loaded) a sysdev_driver.resume phase is carried out, IRQs
-are enabled on the only online CPU, the non-boot CPUs are enabled, and the
-resume_noirq (or thaw_noirq or restore_noirq) phase begins.
-
-Code to actually enter and exit the system-wide low power state sometimes
-involves hardware details that are only known to the boot firmware, and
-may leave a CPU running software (from SRAM or flash memory) that monitors
-the system and manages its wakeup sequence.
+for the given device during all power transitions, instead of the respective
+subsystem-level callbacks. Specifically, if a device's pm_domain pointer is
+not NULL, the ->suspend() callback from the object pointed to by it will be
+executed instead of its subsystem's (e.g. bus type's) ->suspend() callback and
+anlogously for all of the remaining callbacks. In other words, power management
+domain callbacks, if defined for the given device, always take precedence over
+the callbacks provided by the device's subsystem (e.g. bus type).
+
+The support for device power management domains is only relevant to platforms
+needing to use the same device driver power management callbacks in many
+different power domain configurations and wanting to avoid incorporating the
+support for power domains into subsystem-level callbacks, for example by
+modifying the platform bus type. Other platforms need not implement it or take
+it into account in any way.
Device Low Power (suspend) States
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index 654097b130b4..b24875b1ced5 100644
--- a/Documentation/power/runtime_pm.txt
+++ b/Documentation/power/runtime_pm.txt
@@ -501,13 +501,29 @@ helper functions described in Section 4. In that case, pm_runtime_resume()
should be used. Of course, for this purpose the device's run-time PM has to be
enabled earlier by calling pm_runtime_enable().
-If the device bus type's or driver's ->probe() or ->remove() callback runs
+If the device bus type's or driver's ->probe() callback runs
pm_runtime_suspend() or pm_runtime_idle() or their asynchronous counterparts,
they will fail returning -EAGAIN, because the device's usage counter is
-incremented by the core before executing ->probe() and ->remove(). Still, it
-may be desirable to suspend the device as soon as ->probe() or ->remove() has
-finished, so the PM core uses pm_runtime_idle_sync() to invoke the
-subsystem-level idle callback for the device at that time.
+incremented by the driver core before executing ->probe(). Still, it may be
+desirable to suspend the device as soon as ->probe() has finished, so the driver
+core uses pm_runtime_put_sync() to invoke the subsystem-level idle callback for
+the device at that time.
+
+Moreover, the driver core prevents runtime PM callbacks from racing with the bus
+notifier callback in __device_release_driver(), which is necessary, because the
+notifier is used by some subsystems to carry out operations affecting the
+runtime PM functionality. It does so by calling pm_runtime_get_sync() before
+driver_sysfs_remove() and the BUS_NOTIFY_UNBIND_DRIVER notifications. This
+resumes the device if it's in the suspended state and prevents it from
+being suspended again while those routines are being executed.
+
+To allow bus types and drivers to put devices into the suspended state by
+calling pm_runtime_suspend() from their ->remove() routines, the driver core
+executes pm_runtime_put_sync() after running the BUS_NOTIFY_UNBIND_DRIVER
+notifications in __device_release_driver(). This requires bus types and
+drivers to make their ->remove() callbacks avoid races with runtime PM directly,
+but also it allows of more flexibility in the handling of devices during the
+removal of their drivers.
The user space can effectively disallow the driver of the device to power manage
it at run time by changing the value of its /sys/devices/.../power/control
@@ -566,11 +582,6 @@ to do this is:
pm_runtime_set_active(dev);
pm_runtime_enable(dev);
-The PM core always increments the run-time usage counter before calling the
-->prepare() callback and decrements it after calling the ->complete() callback.
-Hence disabling run-time PM temporarily like this will not cause any run-time
-suspend callbacks to be lost.
-
7. Generic subsystem callbacks
Subsystems may wish to conserve code space by using the set of generic power