linux-toradex.git/Documentation/power/devices.txt, branch v3.4.2

PM / Sleep: Introduce "late suspend" and "early resume" of devices

2012-01-29T19:38:29+00:00

The current device suspend/resume phases during system-wide power
transitions appear to be insufficient for some platforms that want
to use the same callback routines for saving device states and
related operations during runtime suspend/resume as well as during
system suspend/resume.  In principle, they could point their
.suspend_noirq() and .resume_noirq() to the same callback routines
as their .runtime_suspend() and .runtime_resume(), respectively,
but at least some of them require device interrupts to be enabled
while the code in those routines is running.

It also makes sense to have device suspend-resume callbacks that will
be executed with runtime PM disabled and with device interrupts
enabled in case someone needs to run some special code in that
context during system-wide power transitions.

Apart from this, .suspend_noirq() and .resume_noirq() were introduced
as a workaround for drivers using shared interrupts and failing to
prevent their interrupt handlers from accessing suspended hardware.
It appears to be better not to use them for other porposes, or we may
have to deal with some serious confusion (which seems to be happening
already).

For the above reasons, introduce new device suspend/resume phases,
"late suspend" and "early resume" (and analogously for hibernation)
whose callback will be executed with runtime PM disabled and with
device interrupts enabled and whose callback pointers generally may
point to runtime suspend/resume routines.

Signed-off-by: Rafael J. Wysocki 
Reviewed-by: Mark Brown 
Reviewed-by: Kevin Hilman

PM: Run the driver callback directly if the subsystem one is not there

2011-12-21T21:01:05+00:00

Make the PM core execute driver PM callbacks directly if the
corresponding subsystem callbacks are not present.

There are three reasons for doing that.  First, it reflects the
behavior of drivers/base/dd.c:really_probe() that runs the driver's
.probe() callback directly if the bus type's one is not defined, so
this change will remove one arbitrary difference between the PM core
and the remaining parts of the driver core.  Second, it will allow
some subsystems, whose PM callbacks don't do anything except for
executing driver callbacks, to be simplified quite a bit by removing
those "forward-only" callbacks.  Finally, it will allow us to remove
one level of indirection in the system suspend and resume code paths
where it is not necessary, which is going to lead to less debug noise
with initcall_debug passed in the kernel command line (messages won't
be printed for driverless devices whose subsystems don't provide
PM callbacks among other things).

Signed-off-by: Rafael J. Wysocki

PM / Sleep: Update documentation related to system wakeup

2011-11-28T21:14:45+00:00

The system wakeup section of Documentation/power/devices.txt is
outdated, so make it agree with the current code.

Signed-off-by: Rafael J. Wysocki

PM / Sleep: Correct inaccurate information in devices.txt

2011-11-28T21:14:27+00:00

The documentation file Documentation/power/devices.txt contains some
information that isn't correct any more due to code modifications
made after that file had been created (or updated last time).  Fix
this.

Signed-off-by: Rafael J. Wysocki

PM / Domains: Document how PM domains are used by the PM core

2011-11-28T21:14:19+00:00

The current power management documentation in Documentation/power/
either doesn't cover PM domains at all, or gives inaccurate
information about them, so update the relevant files in there to
follow the code.

Signed-off-by: Rafael J. Wysocki

PM / Hibernate: Freeze kernel threads after preallocating memory

2011-10-16T21:28:52+00:00

There is a problem with the current ordering of hibernate code which
leads to deadlocks in some filesystems' memory shrinkers.  Namely,
some filesystems use freezable kernel threads that are inactive when
the hibernate memory preallocation is carried out.  Those same
filesystems use memory shrinkers that may be triggered by the
hibernate memory preallocation.  If those memory shrinkers wait for
the frozen kernel threads, the hibernate process deadlocks (this
happens with XFS, for one example).

Apparently, it is not technically viable to redesign the filesystems
in question to avoid the situation described above, so the only
possible solution of this issue is to defer the freezing of kernel
threads until the hibernate memory preallocation is done, which is
implemented by this change.

Unfortunately, this requires the memory preallocation to be done
before the "prepare" stage of device freeze, so after this change the
only way drivers can allocate additional memory for their freeze
routines in a clean way is to use PM notifiers.

Reported-by: Christoph 
Signed-off-by: Rafael J. Wysocki

PM: Update the policy on default wakeup settings

2011-10-16T21:28:51+00:00

This patch (as1485) documents a change to the kernel's default wakeup
policy.  Devices that forward wakeup requests between buses should be
enabled for wakeup by default.

Signed-off-by: Alan Stern 
Signed-off-by: Rafael J. Wysocki

PM / Runtime: Update documentation of interactions with system sleep

2011-07-02T12:30:09+00:00

The documents describing the interactions between runtime PM and
system sleep generally refer to the model in which the system sleep
state is entered through a global firmware or hardware operation.
As a result, some recommendations given in there are not entirely
suitable for systems in which this is not the case.  Update the
documentation to take the existence of those systems into account.

Signed-off-by: Rafael J. Wysocki 
Reviewed-by: Kevin Hilman

PM / Domains: Rename struct dev_power_domain to struct dev_pm_domain

2011-07-02T12:29:54+00:00

The naming convention used by commit 7538e3db6e015e890825fbd9f86599b
(PM: Add support for device power domains), which introduced the
struct dev_power_domain type for representing device power domains,
evidently confuses some developers who tend to think that objects
of this type must correspond to "power domains" as defined by
hardware, which is not the case.  Namely, at the kernel level, a
struct dev_power_domain object can represent arbitrary set of devices
that are mutually dependent power management-wise and need not belong
to one hardware power domain.  To avoid that confusion, rename struct
dev_power_domain to struct dev_pm_domain and rename the related
pointers in struct device and struct pm_clk_notifier_block from
pwr_domain to pm_domain.

Signed-off-by: Rafael J. Wysocki 
Acked-by: Kevin Hilman

PM / Domains: Update documentation

2011-06-21T21:25:32+00:00

Commit 4d27e9dcff00a6425d779b065ec8892e4f391661 (PM: Make power
domain callbacks take precedence over subsystem ones) forgot to
update the device power management documentation to take changes
made by it into account.  Correct that mistake.

Signed-off-by: Rafael J. Wysocki