pm(7D) (man pages section 7: Device and Network Interfaces)

man pages section 7: Device and Network Interfaces

pm(7D)

NAME

pm- Power Management driver

SYNOPSIS

/dev/pm

DESCRIPTION

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.

Power Management Framework

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.

OBSOLETE IOCTLS

All of the ioctl commands in this section are obsolete and will be removed in a future release. See the NEW IOCTLS section of this man page for new commands.

For this set of ioctl commands, arg (see ioctl(2)) points to a structure of type pm_request defined in <sys/pm.h>:

typedef struct {
     char *who;        /* device to configure */
     int  select;      /* selects the component or dependent of the device */
     int  level;       /* power level or threshold value */
     char *dependent;  /* holds name of dependent */
     int  size;        /* size of dependent buffer */ 
} pm_request;

The fields should contain the following data:

who: Pointer to the name of the device to be configured. This may be the name of a device special file or any trailing substring of the physical path to the device.
select: Non-negative integer specifying the component or dependent being configured. The numbering starts at zero.
level: Non-negative integer specifying the threshold value in seconds or the desired power level.
dependent: Pointer to a buffer which contains the name of a device on which this device has a dependency. It uses the same format as the who field.
size: Size of the dependent buffer.

Not all fields are used in each command.

PM_DISABLE_AUTOPM

The device named by who is disabled from being power managed by framework. The caller will power manage the device directly using the commands below. If this command is not successfully executed, subsequent PM_SET_CUR_PWR calls will fail. This command is obsolete and will be removed in a future release. Use PM_DIRECT_PM instead.

Error codes:

EBUSY: Device already disabled from being power managed by framework.
EPERM: Caller is neither superuser nor owner of the device.

PM_GET_NORM_PWR

The normal power level of the component select of the device named by who is returned. The normal power level of the component is the power level to which the component will be set when it becomes busy again. This command is obsolete and will be removed in a future release. Use PM_GET_FULL_POWER instead.

Error codes:

EINVAL: Device component out of range.
EIO: Device has no power-manageable components.

PM_GET_CUR_PWR

The current power level of component select of the device named by who is returned. This command is obsolete and will be removed in a future release. Please use PM_GET_CURRENT_POWER instead.

Error codes:

EINVAL: Device component out of range.
EAGAIN: Device component level is not currently known.

PM_SET_CUR_PWR

Component select of the device named by who is brought to power level level. If select is not 0 and component 0 of the device is at power level 0, component 0 is brought to its normal power level. Each component of each device which depends on this device is brought to its normal power level. Each component of each ancestor of each device affected is brought to its normal power level. This command is obsolete and will be removed in a future release. Use PM_SET_CURRENT_POWER instead.

Error codes:

EINVAL: Device component out of range, or power level < 0.
EIO: Failed to power device or its ancestors or its dependents or their ancestors.
EPERM: Caller is neither superuser nor owner of the device.

PM_REENABLE_AUTOPM

The device named by who is re-enabled for Power Management by the framework. By default, all configured devices are power managed by the framework. This command is obsolete and will be removed in a future release. Use PM_RELEASE_DIRECT_PM instead.

Error codes:

EINVAL: Device already being power managed by the framework.
EPERM: Caller is neither super-user nor owner of the device.

NEW IOCTLS

The ioctl commands in this section replace the obsolete commands listed above and take a pointer to a different structure and support more complete functionality.

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(3) */
          int  component;     /* the component of the device */
          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(3). 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 */
   int     event;       /* type of event */
   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. 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.

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.

ERRORS

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.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface stability	Unstable (Interfaces under OBSOLETE IOCTLS are obsolete.)

pm(7D)

NAME

SYNOPSIS

DESCRIPTION

Power Management Framework

OBSOLETE IOCTLS

NEW IOCTLS

ERRORS

ATTRIBUTES

SEE ALSO