wakeup_source_add() adds an item into wakeup_sources list.

There is no need to call synchronize_rcu() at this point.

Its only needed in wakeup_source_remove()
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

It turns out that some PCI devices are only found to be
wakeup-capable during registration, in which case, when
device_set_wakeup_capable() is called, device_is_registered() already
returns 'true' for the given device, but dpm_sysfs_add() hasn't been
called for it yet.  This leads to situations in which the device's
power.can_wakeup flag is not set as requested because of failing
wakeup_sysfs_add() and its wakeup-related sysfs files are not
created, although they should be present.  This is a post-2.6.38
regression introduced by commit cb8f51bd
(PM: Do not create wakeup sysfs files for devices that cannot wake
up).

To work around this problem initialize the device's power.entry
field to an empty list head and make device_set_wakeup_capable()
check if it is still empty before attempting to add the devices
wakeup-related sysfs files with wakeup_sysfs_add().  Namely, if
power.entry is still empty at this point, device_pm_add() hasn't been
called yet for the device and its wakeup-related files will be
created later, so device_set_wakeup_capable() doesn't have to create
them.
Reported-and-tested-by: NTino Keitel <tino.keitel@tikei.de>
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>

Currently, wakeup sysfs attributes are created for all devices,
regardless of whether or not they are wakeup-capable.  This is
excessive and complicates wakeup device identification from user
space (i.e. to identify wakeup-capable devices user space has to read
/sys/devices/.../power/wakeup for all devices and see if they are not
empty).

Fix this issue by avoiding to create wakeup sysfs files for devices
that cannot wake up the system from sleep states (i.e. whose
power.can_wakeup flags are unset during registration) and modify
device_set_wakeup_capable() so that it adds (or removes) the relevant
sysfs attributes if a device's wakeup capability status is changed.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

Since pm_save_wakeup_count() has just been changed to clear
events_check_enabled unconditionally before checking if there are
any new wakeup events registered since the last read from
/sys/power/wakeup_count, the detection of wakeup events during
suspend may be disabled, after it's been enabled, by writing a
"wrong" value back to /sys/power/wakeup_count.  For this reason,
it is not necessary to update events_check_enabled in
pm_get_wakeup_count() any more.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

According to Documentation/ABI/testing/sysfs-power, the
/sys/power/wakeup_count interface should only make the kernel react
to wakeup events during suspend if the last write to it has been
successful.  However, if /sys/power/wakeup_count is written to two
times in a row, where the first write is successful and the second
is not, the kernel will still react to wakeup events during suspend
due to a bug in pm_save_wakeup_count().

Fix the bug by making pm_save_wakeup_count() clear
events_check_enabled unconditionally before checking if there are
any new wakeup events registered since the previous read from
/sys/power/wakeup_count.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

The memory barrier in wakeup_source_deactivate() is supposed to
prevent the callers of pm_wakeup_pending() and pm_get_wakeup_count()
from seeing the new value of events_in_progress (0, in particular)
and the old value of event_count at the same time.  However, if
wakeup_source_deactivate() is executed by CPU0 and, for instance,
pm_wakeup_pending() is executed by CPU1, where both processors can
reorder operations, the memory barrier in wakeup_source_deactivate()
doesn't affect CPU1 which can reorder reads.  In that case CPU1 may
very well decide to fetch event_count before it's modified and
events_in_progress after it's been updated, so pm_wakeup_pending()
may fail to detect a wakeup event.  This issue can be addressed by
using a single atomic variable to store both events_in_progress
and event_count, so that they can be updated together in a single
atomic operation.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

To avoid confusion with the meaning and return value of
pm_check_wakeup_events() replace it with pm_wakeup_pending() that
will work the other way around (ie. return true when system-wide
power transition should be aborted).
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

There may be wakeup sources that aren't associated with any devices
and their statistics information won't be available from sysfs. Also,
for debugging purposes it is convenient to have all of the wakeup
sources statistics available from one place.  For these reasons,
introduce new file "wakeup_sources" in debugfs containing those
statistics.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>

Introduce struct wakeup_source for representing system wakeup sources
within the kernel and for collecting statistics related to them.
Make the recently introduced helper functions pm_wakeup_event(),
pm_stay_awake() and pm_relax() use struct wakeup_source objects
internally, so that wakeup statistics associated with wakeup devices
can be collected and reported in a consistent way (the definition of
pm_relax() is changed, which is harmless, because this function is
not called directly by anyone yet).  Introduce new wakeup-related
sysfs device attributes in /sys/devices/.../power for reporting the
device wakeup statistics.

Change the global wakeup events counters event_count and
events_in_progress into atomic variables, so that it is not necessary
to acquire a global spinlock in pm_wakeup_event(), pm_stay_awake()
and pm_relax(), which should allow us to avoid lock contention in
these functions on SMP systems with many wakeup devices.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>

Originally, pm_wakeup_event() uses struct delayed_work objects,
allocated with GFP_ATOMIC, to schedule the execution of pm_relax()
in future.  However, as noted by Alan Stern, it is not necessary to
do that, because all pm_wakeup_event() calls can use one static timer
that will always be set to expire at the latest time passed to
pm_wakeup_event().

The modifications are based on the example code posted by Alan.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

One of the arguments during the suspend blockers discussion was that
the mainline kernel didn't contain any mechanisms making it possible
to avoid races between wakeup and system suspend.

Generally, there are two problems in that area.  First, if a wakeup
event occurs exactly when /sys/power/state is being written to, it
may be delivered to user space right before the freezer kicks in, so
the user space consumer of the event may not be able to process it
before the system is suspended.  Second, if a wakeup event occurs
after user space has been frozen, it is not generally guaranteed that
the ongoing transition of the system into a sleep state will be
aborted.

To address these issues introduce a new global sysfs attribute,
/sys/power/wakeup_count, associated with a running counter of wakeup
events and three helper functions, pm_stay_awake(), pm_relax(), and
pm_wakeup_event(), that may be used by kernel subsystems to control
the behavior of this attribute and to request the PM core to abort
system transitions into a sleep state already in progress.

The /sys/power/wakeup_count file may be read from or written to by
user space.  Reads will always succeed (unless interrupted by a
signal) and return the current value of the wakeup events counter.
Writes, however, will only succeed if the written number is equal to
the current value of the wakeup events counter.  If a write is
successful, it will cause the kernel to save the current value of the
wakeup events counter and to abort the subsequent system transition
into a sleep state if any wakeup events are reported after the write
has returned.

[The assumption is that before writing to /sys/power/state user space
will first read from /sys/power/wakeup_count.  Next, user space
consumers of wakeup events will have a chance to acknowledge or
veto the upcoming system transition to a sleep state.  Finally, if
the transition is allowed to proceed, /sys/power/wakeup_count will
be written to and if that succeeds, /sys/power/state will be written
to as well.  Still, if any wakeup events are reported to the PM core
by kernel subsystems after that point, the transition will be
aborted.]

Additionally, put a wakeup events counter into struct dev_pm_info and
make these per-device wakeup event counters available via sysfs,
so that it's possible to check the activity of various wakeup event
sources within the kernel.

To illustrate how subsystems can use pm_wakeup_event(), make the
low-level PCI runtime PM wakeup-handling code use it.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>
Acked-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>
Acked-by: Nmarkgross <markgross@thegnar.org>
Reviewed-by: NAlan Stern <stern@rowland.harvard.edu>