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/dev/pm
The Power Management ( pm) driver provides an interface for applications to configure devices within the system for Power Management. The interface is provided through ioctl(2) commands. The pm driver may be accessed using /dev/pm.
The Power Management framework model allows the system to be viewed as a collection of devices. Each device is a collection of components that comprise the smallest power manageable units. The device driver controls the definition of a device's power manageable components.
A component can either be busy or idle at the current power level. Normally, the Power Management framework takes an idle component to the next lower power level. The Power Management framework uses two factors to determine this transition: the component must have been idle for at least the threshold time, and the device to which the component belongs must satisfy any dependency requirements. A dependency occurs when a device requires another device to be power managed before it can be power managed. Dependencies occur on a per device basis: when a dependency exists, no components of a device may be managed unless all the devices it depends upon are first power managed.
Using the commands below, an application may take control of the Power Management of a device from the Power Management framework driver and manage the transition of device power levels directly.
For this set of ioctl commands, arg (see ioctl(2)) points to a structure of type pm_req defined in <sys/pm.h>:
typedef struct pm_req {
char *physpath; /* physical path of device */
/* to configure. See libdevinfo(3LIB) */
int component; /* device component */
int value; /* power level, threshold value, or count */
void *data; /* command-dependent variable-sized data */
size_t datasize; /* size of data buffer */
} pm_req_t;
The fields should contain the following data:
physpath
Pointer to the physical path of a device. See libdevinfo(3LIB). For example, for the device /devices/pseudo/pm@0:pm the physpath value would be /pseudo/pm@0.
component
Non-negative integer specifying which component is being configured. The numbering starts at zero.
value
Non-negative integer specifying the threshold value in seconds or the desired power level, or the number of levels being specified.
data
Pointer to a buffer which contains or receives variable-sized data, such as the name of a device upon which this device has a dependency.
size
Size of the data buffer.
Not all fields are used in each command.
PM_DIRECT_PM
The device named by physpath is disabled from being power managed by the framework. The caller will power manage the device directly using the PM_DIRECT_NOTIFY, PM_GET_TIME_IDLE and PM_GET_CURRENT_POWER, PM_GET_FULL_POWER and PM_SET_CURRENT_POWER commands. If the device needs to have its power level changed either because its driver calls pm_raise_power(9F), pm_lower_power(9F), or pm_power_has_changed(9F) or because the device is the parent of another device that is changing power level or a device that this device depends on is changing power level, then the power level change of the device will be blocked and the caller will be notified as described below for the PM_DIRECT_NOTIFY command. Error codes:
EBUSY
Device already disabled for Power Management by framework.
EPERM
Caller is neither superuser nor effective group ID of 0.
PM_RELEASE_DIRECT_PM
The device named by physpath (which must have been the target of a PM_DIRECT_PM command) is re-enabled for Power Management by the framework. Error codes:
EINVAL
Device component out of range.
PM_DIRECT_NOTIFY PM_DIRECT_NOTIFY_WAIT
These commands allow the process that is directly power managing a device to be notified of events that could change the power level of the device. When such an event occurs, this command returns information about the event. arg (see ioctl(2)) points to a structure of type pm_state_change defined in <sys/pm.h>:
typedef struct pm_state_change {
char *physpath; /* device which has changed state */
int component; /* which component changed state */
#if defined(_BIG_ENDIAN)
ushort_t flags; /* PSC_EVENT_LOST, PSC_ALL_LOWEST */
ushort_t event; /* type of event */
#else
ushort_t event; /* type of event *
ushort_t flags; /* PSC_EVENT_LOST, PSC_ALL_LOWEST */
#endif
time_t timestamp; /* time of state change */+
int old_level; /* power level changing from */
int new_level; /* power level changing to */
size_t size; /* size of buffer physpath points to */
} pm_state_change_t;
When an event occurs, the struct pointed to by arg is filled in. If the
event type is PSC_PENDING_CHANGE, then the information in the rest of the
struct describes an action that the framework would have taken if the device
were not directly power managed by the caller. The caller is responsible for
completing the indicated level changes using PM_SET_CURRENT_POWER below.
An event type of PSC_HAS_CHANGED indicates that the driver for the
directly power managed device has called pm_power_has_changed(9F) due to
the device changing power on its own. It is provided to allow the caller to
track the power state of the device.
The system keeps events in a circular buffer. If the buffer overflow, the
oldest events are lost and when the event that next follows a lost event is
retrieved it will have PSC_EVENT_LOST set in flags.
PM_DIRECT_NOTIFY returns EWOULDBLOCK if no event is pending, and
PM_DIRECT_NOTIFY_WAIT blocks until an event is available.
pm also supports the poll(2) interface. When an event is pending a
poll(2) call that includes a file descriptor for /dev/pm and that
has POLLIN or POLLRDNORM set in its event mask will return.
PM_SET_CURRENT_POWER
Component component of the device named by physpath (which must contain the physical path of a device against which the process has issued a PM_DIRECT_PM command) is set to power level value. If all components of the device named by physpath were at level 0, value is non-zero and some device has a dependency on this device, then all components of that device will be brought to full power before this command returns. Similarly, if the parent of the target device is powered off, then it will be brought up as needed before this command returns. When PM_SET_CURRENT_POWER is issued against a device, the resulting power change is included in the event list for PM_DIRECT_NOTIFY. Error codes:
EINVAL
Device component out of range, or power level < 0.
EIO
Failed to power device or its ancestors or the devices on which this device has dependency or their ancestors. Note that this may not indicate a failure, the device driver may have rejected the command as inappropriate because the component has become busy.
EPERM
Caller has not previously issued a successful PM_DIRECT_PM command against this device.
PM_GET_FULL_POWER
The highest supported power level of component component of the device named by physpath is returned.
PM_GET_CURRENT_POWER
The current power level of component component of the device named by physpath is returned. Error codes:
EAGAIN
Device component power level is not currently known.
PM_GET_TIME_IDLE
PM_GET_TIME_IDLE returns the number of seconds that component component of the device named by physpath has been idle. If the device is not idle, then 0 is returned. Note that because the state of the device may change between the time the process issues the PM_GET_TIME_IDLE command and the time the process issues a PM_SET_CURRENT_POWER command to reduce the power level of an idle component, the process must be prepared to deal with a PM_SET_CURRENT_POWER command returning failure because the driver has rejected the command as inappropriate because the device component has become busy. This can be differentiated from other types of failures by issuing the PM_GET_TIME_IDLE command again to see if the component has become busy.
Upon error, the commands will return -1, and set errno. In addition to the error codes listed above by command, the following error codes are common to all commands:
EFAULT
Bad address passed in as argument.
ENODEV
Device is not power manageable, or device is not configured.
ENXIO
Too many opens attempted.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Interface stability | Unstable |
pmconfig(1M), Intro(2), ioctl(2), libdevinfo(3LIB), power.conf(4), attributes(5), attach(9E), detach(9E), power(9E), pm_busy_component(9F), pm_idle_component(9F), pm_lower_power(9F), pm_power_has_changed(9F), pm_raise_power(9F)
Writing Device Drivers