Commit 5841eb64 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki

PM / Domains: Document how PM domains are used by the PM core

The current power management documentation in Documentation/power/
either doesn't cover PM domains at all, or gives inaccurate
information about them, so update the relevant files in there to
follow the code.
Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
parent bb58dd5d
......@@ -123,9 +123,10 @@ please refer directly to the source code for more information about it.
Subsystem-Level Methods
-----------------------
The core methods to suspend and resume devices reside in struct dev_pm_ops
pointed to by the pm member of struct bus_type, struct device_type and
struct class. They are mostly of interest to the people writing infrastructure
for buses, like PCI or USB, or device type and device class drivers.
pointed to by the ops member of struct dev_pm_domain, or by the pm member of
struct bus_type, struct device_type and struct class. They are mostly of
interest to the people writing infrastructure for platforms and buses, like PCI
or USB, or device type and device class drivers.
Bus drivers implement these methods as appropriate for the hardware and the
drivers using it; PCI works differently from USB, and so on. Not many people
......@@ -251,18 +252,29 @@ various phases always run after tasks have been frozen and before they are
unfrozen. Furthermore, the *_noirq phases run at a time when IRQ handlers have
been disabled (except for those marked with the IRQ_WAKEUP flag).
All phases use bus, type, or class callbacks (that is, methods defined in
dev->bus->pm, dev->type->pm, or dev->class->pm). These callbacks are mutually
exclusive, so if the device type provides a struct dev_pm_ops object pointed to
by its pm field (i.e. both dev->type and dev->type->pm are defined), the
callbacks included in that object (i.e. dev->type->pm) will be used. Otherwise,
if the class provides a struct dev_pm_ops object pointed to by its pm field
(i.e. both dev->class and dev->class->pm are defined), the PM core will use the
callbacks from that object (i.e. dev->class->pm). Finally, if the pm fields of
both the device type and class objects are NULL (or those objects do not exist),
the callbacks provided by the bus (that is, the callbacks from dev->bus->pm)
will be used (this allows device types to override callbacks provided by bus
types or classes if necessary).
All phases use PM domain, bus, type, or class callbacks (that is, methods
defined in dev->pm_domain->ops, dev->bus->pm, dev->type->pm, or dev->class->pm).
These callbacks are regarded by the PM core as mutually exclusive. Moreover,
PM domain callbacks always take precedence over bus, type and class callbacks,
while type callbacks take precedence over bus and class callbacks, and class
callbacks take precedence over bus callbacks. To be precise, the following
rules are used to determine which callback to execute in the given phase:
1. If dev->pm_domain is present, the PM core will attempt to execute the
callback included in dev->pm_domain->ops. If that callback is not
present, no action will be carried out for the given device.
2. Otherwise, if both dev->type and dev->type->pm are present, the callback
included in dev->type->pm will be executed.
3. Otherwise, if both dev->class and dev->class->pm are present, the
callback included in dev->class->pm will be executed.
4. Otherwise, if both dev->bus and dev->bus->pm are present, the callback
included in dev->bus->pm will be executed.
This allows PM domains and device types to override callbacks provided by bus
types or device classes if necessary.
These callbacks may in turn invoke device- or driver-specific methods stored in
dev->driver->pm, but they don't have to.
......
......@@ -44,17 +44,24 @@ struct dev_pm_ops {
};
The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks
are executed by the PM core for either the power domain, or the device type
(if the device power domain's struct dev_pm_ops does not exist), or the class
(if the device power domain's and type's struct dev_pm_ops object does not
exist), or the bus type (if the device power domain's, type's and class'
struct dev_pm_ops objects do not exist) of the given device, so the priority
order of callbacks from high to low is that power domain callbacks, device
type callbacks, class callbacks and bus type callbacks, and the high priority
one will take precedence over low priority one. The bus type, device type and
class callbacks are referred to as subsystem-level callbacks in what follows,
and generally speaking, the power domain callbacks are used for representing
power domains within a SoC.
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.
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, subsystems can use the pm_runtime_irq_safe() helper function
......
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