PM_EVENT_SUSPEND -- quiesce the driver and put hardware into a low-power
state. When used with system sleep states like "suspend-to-RAM" or
"standby", the upcoming resume() call will often be able to rely on
- state kept in hardware, or issue system wakeup events. When used
- instead with suspend-to-disk, few devices support this capability;
- most are completely powered off.
+ state kept in hardware, or issue system wakeup events.
+
+ PM_EVENT_HIBERNATE -- Put hardware into a low-power state and enable wakeup
+ events as appropriate. It is only used with hibernation
+ (suspend-to-disk) and few devices are able to wake up the system from
+ this state; most are completely powered off.
PM_EVENT_FREEZE -- quiesce the driver, but don't necessarily change into
any low power mode. A system snapshot is about to be taken, often
wakeup events nor DMA are allowed.
To enter "standby" (ACPI S1) or "Suspend to RAM" (STR, ACPI S3) states, or
-the similarly named APM states, only PM_EVENT_SUSPEND is used; for "Suspend
-to Disk" (STD, hibernate, ACPI S4), all of those event codes are used.
+the similarly named APM states, only PM_EVENT_SUSPEND is used; the other event
+codes are used for hibernation ("Suspend to Disk", STD, ACPI S4).
There's also PM_EVENT_ON, a value which never appears as a suspend event
but is sometimes used to record the "not suspended" device state.
to shift to lower voltage settings and reduce the power cost of executing
a given number of instructions. (Without voltage adjustment, it's rare
for cpufreq to save much power; the cost-per-instruction must go down.)
-
-
-/sys/devices/.../power/state files
-==================================
-For now you can also test some of this functionality using sysfs.
-
- DEPRECATED: USE "power/state" ONLY FOR DRIVER TESTING, AND
- AVOID USING dev->power.power_state IN DRIVERS.
-
- THESE WILL BE REMOVED. IF THE "power/state" FILE GETS REPLACED,
- IT WILL BECOME SOMETHING COUPLED TO THE BUS OR DRIVER.
-
-In each device's directory, there is a 'power' directory, which contains
-at least a 'state' file. The value of this field is effectively boolean,
-PM_EVENT_ON or PM_EVENT_SUSPEND.
-
- * Reading from this file displays a value corresponding to
- the power.power_state.event field. All nonzero values are
- displayed as "2", corresponding to a low power state; zero
- is displayed as "0", corresponding to normal operation.
-
- * Writing to this file initiates a transition using the
- specified event code number; only '0', '2', and '3' are
- accepted (without a newline); '2' and '3' are both
- mapped to PM_EVENT_SUSPEND.
-
-On writes, the PM core relies on that recorded event code and the device/bus
-capabilities to determine whether it uses a partial suspend() or resume()
-sequence to change things so that the recorded event corresponds to the
-numeric parameter.
-
- - If the bus requires the irqs-disabled suspend_late()/resume_early()
- phases, writes fail because those operations are not supported here.
-
- - If the recorded value is the expected value, nothing is done.
-
- - If the recorded value is nonzero, the device is partially resumed,
- using the bus.resume() and/or class.resume() methods.
-
- - If the target value is nonzero, the device is partially suspended,
- using the class.suspend() and/or bus.suspend() methods and the
- PM_EVENT_SUSPEND message.
-
-Drivers have no way to tell whether their suspend() and resume() calls
-have come through the sysfs power/state file or as part of entering a
-system sleep state, except that when accessed through sysfs the normal
-parent/child sequencing rules are ignored. Drivers (such as bus, bridge,
-or hub drivers) which expose child devices may need to enforce those rules
-on their own.
projects / linux-2.6-omap-h63xx.git / blobdiff