There are three issues with the i2c bus type's power management
callbacks at the moment.  First, they don't include any hibernate
callbacks, although they should at least include the .restore()
callback (there's no guarantee that the driver will be present in
memory before loading the image kernel and we must restore the
pre-hibernation state of the device).  Second, the "legacy"
callbacks are not going to be invoked by the PM core since the bus
type's pm object is not NULL.  Finally, the system sleep PM
(ie. suspend/resume) callbacks don't check if the device has been
already suspended at run time, in which case they should skip
suspending it.  Also, it looks like the i2c bus type can use the
generic subsystem-level runtime PM callbacks.

For these reasons, rework the system sleep PM callbacks provided by
the i2c bus type to handle hibernation correctly and to invoke the
"legacy" callbacks for drivers that provide them.  In addition to
that make the i2c bus type use the generic subsystem-level runtime
PM callbacks.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Acked-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: NJean Delvare <khali@linux-fr.org>

There are subsystems whose power management callbacks only need to
invoke the callbacks provided by device drivers.  Still, their system
sleep PM callbacks should play well with the runtime PM callbacks,
so that devices suspended at run time can be left in that state for
a system sleep transition.

Provide a set of generic PM callbacks for such subsystems and
define convenience macros for populating dev_pm_ops structures.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

Add new device sysfs attribute, power/control, allowing the user
space to block the run-time power management of the devices.  If this
attribute is set to "on", the driver of the device won't be able to power
manage it at run time (without breaking the rules) and the device will
always be in the full power state (except when the entire system goes
into a sleep state).
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>

Apparently, there are devices that can wake up the system from sleep
states and yet are incapable of generating wake-up events at run
time.  Thus, introduce a flag indicating if given device is capable
of generating run-time wake-up events.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

Introduce a core framework for run-time power management of I/O
devices.  Add device run-time PM fields to 'struct dev_pm_info'
and device run-time PM callbacks to 'struct dev_pm_ops'.  Introduce
a run-time PM workqueue and define some device run-time PM helper
functions at the core level.  Document all these things.

Special thanks to Alan Stern for his help with the design and
multiple detailed reviews of the pereceding versions of this patch
and to Magnus Damm for testing feedback.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Acked-by: NMagnus Damm <damm@igel.co.jp>