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|
Runtime Power Management Framework for I/O Devices
(C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
(C) 2010 Alan Stern <stern@rowland.harvard.edu>
(C) 2014 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
1. Introduction
Support for runtime power management (runtime PM) of I/O devices is provided
at the power management core (PM core) level by means of:
* The power management workqueue pm_wq in which bus types and device drivers can
put their PM-related work items. It is strongly recommended that pm_wq be
used for queuing all work items related to runtime PM, because this allows
them to be synchronized with system-wide power transitions (suspend to RAM,
hibernation and resume from system sleep states). pm_wq is declared in
include/linux/pm_runtime.h and defined in kernel/power/main.c.
* A number of runtime PM fields in the 'power' member of 'struct device' (which
is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can
be used for synchronizing runtime PM operations with one another.
* Three device runtime PM callbacks in 'struct dev_pm_ops' (defined in
include/linux/pm.h).
* A set of helper functions defined in drivers/base/power/runtime.c that can be
used for carrying out runtime PM operations in such a way that the
synchronization between them is taken care of by the PM core. Bus types and
device drivers are encouraged to use these functions.
The runtime PM callbacks present in 'struct dev_pm_ops', the device runtime PM
fields of 'struct dev_pm_info' and the core helper functions provided for
runtime PM are described below.
2. Device Runtime PM Callbacks
There are three device runtime PM callbacks defined in 'struct dev_pm_ops':
struct dev_pm_ops {
...
int (*runtime_suspend)(struct device *dev);
int (*runtime_resume)(struct device *dev);
int (*runtime_idle)(struct device *dev);
...
};
The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks
are executed by the PM core for the device's subsystem that may be either of
the following:
1. PM domain of the device, if the device's PM domain object, dev->pm_domain,
is present.
2. Device type of the device, if both dev->type and dev->type->pm are present.
3. Device class of the device, if both dev->class and dev->class->pm are
present.
4. Bus type of the device, if both dev->bus and dev->bus->pm are present.
If the subsystem chosen by applying the above rules doesn't provide the relevant
callback, the PM core will invoke the corresponding driver callback stored in
dev->driver->pm directly (if present).
The PM core always checks which callback to use in the order given above, so the
priority order of callbacks from high to low is: PM domain, device type, class
and bus type. Moreover, the high-priority one will always take precedence over
a low-priority one. The PM domain, bus type, device type and class callbacks
are referred to as subsystem-level callbacks in what follows.
By default, the callbacks are always invoked in process context with interrupts
enabled. However, the pm_runtime_irq_safe() helper function can be used to tell
the PM core that it is safe to run the ->runtime_suspend(), ->runtime_resume()
and ->runtime_idle() callbacks for the given device in atomic context with
interrupts disabled. This implies that the callback routines in question must
not block or sleep, but it also means that the synchronous helper functions
listed at the end of Section 4 may be used for that device within an interrupt
handler or generally in an atomic context.
The subsystem-level suspend callback, if present, is _entirely_ _responsible_
for handling the suspend of the device as appropriate, which may, but need not
include executing the device driver's own ->runtime_suspend() callback (from the
PM core's point of view it is not necessary to implement a ->runtime_suspend()
callback in a device driver as long as the subsystem-level suspend callback
knows what to do to handle the device).
* Once the subsystem-level suspend callback (or the driver suspend callback,
if invoked directly) has completed successfully for the given device, the PM
core regards the device as suspended, which need not mean that it has been
put into a low power state. It is supposed to mean, however, that the
device will not process data and will not communicate with the CPU(s) and
RAM until the appropriate resume callback is executed for it. The runtime
PM status of a device after successful execution of the suspend callback is
'suspended'.
* If the suspend callback returns -EBUSY or -EAGAIN, the device's runtime PM
status remains 'active', which means that the device _must_ be fully
operational afterwards.
* If the suspend callback returns an error code different from -EBUSY and
-EAGAIN, the PM core regards this as a fatal error and will refuse to run
the helper functions described in Section 4 for the device until its status
is directly set to either 'active', or 'suspended' (the PM core provides
special helper functions for this purpose).
In particular, if the driver requires remote wakeup capability (i.e. hardware
mechanism allowing the device to request a change of its power state, such as
PCI PME) for proper functioning and device_run_wake() returns 'false' for the
device, then ->runtime_suspend() should return -EBUSY. On the other hand, if
device_run_wake() returns 'true' for the device and the device is put into a
low-power state during the execution of the suspend callback, it is expected
that remote wakeup will be enabled for the device. Generally, remote wakeup
should be enabled for all input devices put into low-power states at run time.
The subsystem-level resume callback, if present, is _entirely_ _responsible_ for
handling the resume of the device as appropriate, which may, but need not
include executing the device driver's own ->runtime_resume() callback (from the
PM core's point of view it is not necessary to implement a ->runtime_resume()
callback in a device driver as long as the subsystem-level resume callback knows
what to do to handle the device).
* Once the subsystem-level resume callback (or the driver resume callback, if
invoked directly) has completed successfully, the PM core regards the device
as fully operational, which means that the device _must_ be able to complete
I/O operations as needed. The runtime PM status of the device is then
'active'.
* If the resume callback returns an error code, the PM core regards this as a
fatal error and will refuse to run the helper functions described in Section
4 for the device, until its status is directly set to either 'active', or
'suspended' (by means of special helper functions provided by the PM core
for this purpose).
The idle callback (a subsystem-level one, if present, or the driver one) is
executed by the PM core whenever the device appears to be idle, which is
indicated to the PM core by two counters, the device's usage counter and the
counter of 'active' children of the device.
* If any of these counters is decreased using a helper function provided by
the PM core and it turns out to be equal to zero, the other counter is
checked. If that counter also is equal to zero, the PM core executes the
idle callback with the device as its argument.
The action performed by the idle callback is totally dependent on the subsystem
(or driver) in question, but the expected and recommended action is to check
if the device can be suspended (i.e. if all of the conditions necessary for
suspending the device are satisfied) and to queue up a suspend request for the
device in that case. If there is no idle callback, or if the callback returns
0, then the PM core will attempt to carry out a runtime suspend of the device,
also respecting devices configured for autosuspend. In essence this means a
call to pm_runtime_autosuspend() (do note that drivers needs to update the
device last busy mark, pm_runtime_mark_last_busy(), to control the delay under
this circumstance). To prevent this (for example, if the callback routine has
started a delayed suspend), the routine must return a non-zero value. Negative
error return codes are ignored by the PM core.
The helper functions provided by the PM core, described in Section 4, guarantee
that the following constraints are met with respect to runtime PM callbacks for
one device:
(1) The callbacks are mutually exclusive (e.g. it is forbidden to execute
->runtime_suspend() in parallel with ->runtime_resume() or with another
instance of ->runtime_suspend() for the same device) with the exception that
->runtime_suspend() or ->runtime_resume() can be executed in parallel with
->runtime_idle() (although ->runtime_idle() will not be started while any
of the other callbacks is being executed for the same device).
(2) ->runtime_idle() and ->runtime_suspend() can only be executed for 'active'
devices (i.e. the PM core will only execute ->runtime_idle() or
->runtime_suspend() for the devices the runtime PM status of which is
'active').
(3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device
the usage counter of which is equal to zero _and_ either the counter of
'active' children of which is equal to zero, or the 'power.ignore_children'
flag of which is set.
(4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the
PM core will only execute ->runtime_resume() for the devices the runtime
PM status of which is 'suspended').
Additionally, the helper functions provided by the PM core obey the following
rules:
* If ->runtime_suspend() is about to be executed or there's a pending request
to execute it, ->runtime_idle() will not be executed for the same device.
* A request to execute or to schedule the execution of ->runtime_suspend()
will cancel any pending requests to execute ->runtime_idle() for the same
device.
* If ->runtime_resume() is about to be executed or there's a pending request
to execute it, the other callbacks will not be executed for the same device.
* A request to execute ->runtime_resume() will cancel any pending or
scheduled requests to execute the other callbacks for the same device,
except for scheduled autosuspends.
3. Runtime PM Device Fields
The following device runtime PM fields are present in 'struct dev_pm_info', as
defined in include/linux/pm.h:
struct timer_list suspend_timer;
- timer used for scheduling (delayed) suspend and autosuspend requests
unsigned long timer_expires;
- timer expiration time, in jiffies (if this is different from zero, the
timer is running and will expire at that time, otherwise the timer is not
running)
struct work_struct work;
- work structure used for queuing up requests (i.e. work items in pm_wq)
wait_queue_head_t wait_queue;
- wait queue used if any of the helper functions needs to wait for another
one to complete
spinlock_t lock;
- lock used for synchronization
atomic_t usage_count;
- the usage counter of the device
atomic_t child_count;
- the count of 'active' children of the device
unsigned int ignore_children;
- if set, the value of child_count is ignored (but still updated)
unsigned int disable_depth;
- used for disabling the helper functions (they work normally if this is
equal to zero); the initial value of it is 1 (i.e. runtime PM is
initially disabled for all devices)
int runtime_error;
- if set, there was a fatal error (one of the callbacks returned error code
as described in Section 2), so the helper functions will not work until
this flag is cleared; this is the error code returned by the failing
callback
unsigned int idle_notification;
- if set, ->runtime_idle() is being executed
unsigned int request_pending;
- if set, there's a pending request (i.e. a work item queued up into pm_wq)
enum rpm_request request;
- type of request that's pending (valid if request_pending is set)
unsigned int deferred_resume;
- set if ->runtime_resume() is about to be run while ->runtime_suspend() is
being executed for that device and it is not practical to wait for the
suspend to complete; means "start a resume as soon as you've suspended"
unsigned int run_wake;
- set if the device is capable of generating runtime wake-up events
enum rpm_status runtime_status;
- the runtime PM status of the device; this field's initial value is
RPM_SUSPENDED, which means that each device is initially regarded by the
PM core as 'suspended', regardless of its real hardware status
unsigned int runtime_auto;
- if set, indicates that the user space has allowed the device driver to
power manage the device at run time via the /sys/devices/.../power/control
interface; it may only be modified with the help of the pm_runtime_allow()
and pm_runtime_forbid() helper functions
unsigned int no_callbacks;
- indicates that the device does not use the runtime PM callbacks (see
Section 8); it may be modified only by the pm_runtime_no_callbacks()
helper function
unsigned int irq_safe;
- indicates that the ->runtime_suspend() and ->runtime_resume() callbacks
will be invoked with the spinlock held and interrupts disabled
unsigned int use_autosuspend;
- indicates that the device's driver supports delayed autosuspend (see
Section 9); it may be modified only by the
pm_runtime{_dont}_use_autosuspend() helper functions
unsigned int timer_autosuspends;
- indicates that the PM core should attempt to carry out an autosuspend
when the timer expires rather than a normal suspend
int autosuspend_delay;
- the delay time (in milliseconds) to be used for autosuspend
unsigned long last_busy;
- the time (in jiffies) when the pm_runtime_mark_last_busy() helper
function was last called for this device; used in calculating inactivity
periods for autosuspend
All of the above fields are members of the 'power' member of 'struct device'.
4. Runtime PM Device Helper Functions
The following runtime PM helper functions are defined in
drivers/base/power/runtime.c and include/linux/pm_runtime.h:
void pm_runtime_init(struct device *dev);
- initialize the device runtime PM fields in 'struct dev_pm_info'
void pm_runtime_remove(struct device *dev);
- make sure that the runtime PM of the device will be disabled after
removing the device from device hierarchy
int pm_runtime_idle(struct device *dev);
- execute the subsystem-level idle callback for the device; returns an
error code on failure, where -EINPROGRESS means that ->runtime_idle() is
already being executed; if there is no callback or the callback returns 0
then run pm_runtime_autosuspend(dev) and return its result
int pm_runtime_suspend(struct device *dev);
- execute the subsystem-level suspend callback for the device; returns 0 on
success, 1 if the device's runtime PM status was already 'suspended', or
error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt
to suspend the device again in future and -EACCES means that
'power.disable_depth' is different from 0
int pm_runtime_autosuspend(struct device *dev);
- same as pm_runtime_suspend() except that the autosuspend delay is taken
into account; if pm_runtime_autosuspend_expiration() says the delay has
not yet expired then an autosuspend is scheduled for the appropriate time
and 0 is returned
int pm_runtime_resume(struct device *dev);
- execute the subsystem-level resume callback for the device; returns 0 on
success, 1 if the device's runtime PM status was already 'active' or
error code on failure, where -EAGAIN means it may be safe to attempt to
resume the device again in future, but 'power.runtime_error' should be
checked additionally, and -EACCES means that 'power.disable_depth' is
different from 0
int pm_request_idle(struct device *dev);
- submit a request to execute the subsystem-level idle callback for the
device (the request is represented by a work item in pm_wq); returns 0 on
success or error code if the request has not been queued up
int pm_request_autosuspend(struct device *dev);
- schedule the execution of the subsystem-level suspend callback for the
device when the autosuspend delay has expired; if the delay has already
expired then the work item is queued up immediately
int pm_schedule_suspend(struct device *dev, unsigned int delay);
- schedule the execution of the subsystem-level suspend callback for the
device in future, where 'delay' is the time to wait before queuing up a
suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work
item is queued up immediately); returns 0 on success, 1 if the device's PM
runtime status was already 'suspended', or error code if the request
hasn't been scheduled (or queued up if 'delay' is 0); if the execution of
->runtime_suspend() is already scheduled and not yet expired, the new
value of 'delay' will be used as the time to wait
int pm_request_resume(struct device *dev);
- submit a request to execute the subsystem-level resume callback for the
device (the request is represented by a work item in pm_wq); returns 0 on
success, 1 if the device's runtime PM status was already 'active', or
error code if the request hasn't been queued up
void pm_runtime_get_noresume(struct device *dev);
- increment the device's usage counter
int pm_runtime_get(struct device *dev);
- increment the device's usage counter, run pm_request_resume(dev) and
return its result
int pm_runtime_get_sync(struct device *dev);
- increment the device's usage counter, run pm_runtime_resume(dev) and
return its result
int pm_runtime_get_if_in_use(struct device *dev);
- return -EINVAL if 'power.disable_depth' is nonzero; otherwise, if the
runtime PM status is RPM_ACTIVE and the runtime PM usage counter is
nonzero, increment the counter and return 1; otherwise return 0 without
changing the counter
void pm_runtime_put_noidle(struct device *dev);
- decrement the device's usage counter
int pm_runtime_put(struct device *dev);
- decrement the device's usage counter; if the result is 0 then run
pm_request_idle(dev) and return its result
int pm_runtime_put_autosuspend(struct device *dev);
- decrement the device's usage counter; if the result is 0 then run
pm_request_autosuspend(dev) and return its result
int pm_runtime_put_sync(struct device *dev);
- decrement the device's usage counter; if the result is 0 then run
pm_runtime_idle(dev) and return its result
int pm_runtime_put_sync_suspend(struct device *dev);
- decrement the device's usage counter; if the result is 0 then run
pm_runtime_suspend(dev) and return its result
int pm_runtime_put_sync_autosuspend(struct device *dev);
- decrement the device's usage counter; if the result is 0 then run
pm_runtime_autosuspend(dev) and return its result
void pm_runtime_enable(struct device *dev);
- decrement the device's 'power.disable_depth' field; if that field is equal
to zero, the runtime PM helper functions can execute subsystem-level
callbacks described in Section 2 for the device
int pm_runtime_disable(struct device *dev);
- increment the device's 'power.disable_depth' field (if the value of that
field was previously zero, this prevents subsystem-level runtime PM
callbacks from being run for the device), make sure that all of the
pending runtime PM operations on the device are either completed or
canceled; returns 1 if there was a resume request pending and it was
necessary to execute the subsystem-level resume callback for the device
to satisfy that request, otherwise 0 is returned
int pm_runtime_barrier(struct device *dev);
- check if there's a resume request pending for the device and resume it
(synchronously) in that case, cancel any other pending runtime PM requests
regarding it and wait for all runtime PM operations on it in progress to
complete; returns 1 if there was a resume request pending and it was
necessary to execute the subsystem-level resume callback for the device to
satisfy that request, otherwise 0 is returned
void pm_suspend_ignore_children(struct device *dev, bool enable);
- set/unset the power.ignore_children flag of the device
int pm_runtime_set_active(struct device *dev);
- clear the device's 'power.runtime_error' flag, set the device's runtime
PM status to 'active' and update its parent's counter of 'active'
children as appropriate (it is only valid to use this function if
'power.runtime_error' is set or 'power.disable_depth' is greater than
zero); it will fail and return error code if the device has a parent
which is not active and the 'power.ignore_children' flag of which is unset
void pm_runtime_set_suspended(struct device *dev);
- clear the device's 'power.runtime_error' flag, set the device's runtime
PM status to 'suspended' and update its parent's counter of 'active'
children as appropriate (it is only valid to use this function if
'power.runtime_error' is set or 'power.disable_depth' is greater than
zero)
bool pm_runtime_active(struct device *dev);
- return true if the device's runtime PM status is 'active' or its
'power.disable_depth' field is not equal to zero, or false otherwise
bool pm_runtime_suspended(struct device *dev);
- return true if the device's runtime PM status is 'suspended' and its
'power.disable_depth' field is equal to zero, or false otherwise
bool pm_runtime_status_suspended(struct device *dev);
- return true if the device's runtime PM status is 'suspended'
void pm_runtime_allow(struct device *dev);
- set the power.runtime_auto flag for the device and decrease its usage
counter (used by the /sys/devices/.../power/control interface to
effectively allow the device to be power managed at run time)
void pm_runtime_forbid(struct device *dev);
- unset the power.runtime_auto flag for the device and increase its usage
counter (used by the /sys/devices/.../power/control interface to
effectively prevent the device from being power managed at run time)
void pm_runtime_no_callbacks(struct device *dev);
- set the power.no_callbacks flag for the device and remove the runtime
PM attributes from /sys/devices/.../power (or prevent them from being
added when the device is registered)
void pm_runtime_irq_safe(struct device *dev);
- set the power.irq_safe flag for the device, causing the runtime-PM
callbacks to be invoked with interrupts off
bool pm_runtime_is_irq_safe(struct device *dev);
- return true if power.irq_safe flag was set for the device, causing
the runtime-PM callbacks to be invoked with interrupts off
void pm_runtime_mark_last_busy(struct device *dev);
- set the power.last_busy field to the current time
void pm_runtime_use_autosuspend(struct device *dev);
- set the power.use_autosuspend flag, enabling autosuspend delays
void pm_runtime_dont_use_autosuspend(struct device *dev);
- clear the power.use_autosuspend flag, disabling autosuspend delays
void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
- set the power.autosuspend_delay value to 'delay' (expressed in
milliseconds); if 'delay' is negative then runtime suspends are
prevented
unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
- calculate the time when the current autosuspend delay period will expire,
based on power.last_busy and power.autosuspend_delay; if the delay time
is 1000 ms or larger then the expiration time is rounded up to the
nearest second; returns 0 if the delay period has already expired or
power.use_autosuspend isn't set, otherwise returns the expiration time
in jiffies
It is safe to execute the following helper functions from interrupt context:
pm_request_idle()
pm_request_autosuspend()
pm_schedule_suspend()
pm_request_resume()
pm_runtime_get_noresume()
pm_runtime_get()
pm_ru
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