pm(7D) Devices pm(7D)NAMEpm - Power Management driver
SYNOPSIS
/dev/pm
DESCRIPTION
The Power Management ( pm) driver provides an interface for applica‐
tions 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 con‐
trols the definition of a device's power manageable components.
A component can either be busy or idle at the current power level. Nor‐
mally, 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 depen‐
dency 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 struc‐
ture 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; /* 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 libdev‐
info(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 vari‐
able-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_CUR‐
RENT_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 noti‐
fied 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 over‐
flow, the oldest events are lost and when the event that next fol‐
lows 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 com‐
ponent 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 con‐
figured.
ENXIO Too many opens attempted.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface stability │Unstable │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOpmconfig(1M), intro(2), ioctl(2), libdevinfo(3LIB), power.conf(4),
attributes(5), attach(9E), detach(9E), power(9E), pm_busy_compo‐
nent(9F), pm_idle_component(9F), pm_lower_power(9F),
pm_power_has_changed(9F), pm_raise_power(9F)
Writing Device Drivers
SunOS 5.10 20 Sep 1999 pm(7D)
