[PATCH v8 0/3] PM / wakeup: Show wakeup sources stats in sysfs

[Tri Vo <trong@android.com>]

Userspace can use wakeup_sources debugfs node to plot history of suspend
blocking wakeup sources over device's boot cycle. This information can
then be used (1) for power-specific bug reporting and (2) towards
attributing battery consumption to specific processes over a period of
time.

However, debugfs doesn't have stable ABI. For this reason, create a
'struct device' to expose wakeup sources statistics in sysfs under
/sys/class/wakeup/wakeup<ID>/*.

Patch 1 and 2 do some cleanup to simplify our changes to how wakeup sources are
created. Patch 3 implements wakeup sources stats in sysfs.

Tri Vo (3):
  PM / wakeup: Drop wakeup_source_init(), wakeup_source_prepare()
  PM / wakeup: Use wakeup_source_register() in wakelock.c
  PM / wakeup: Show wakeup sources stats in sysfs

 Documentation/ABI/testing/sysfs-class-wakeup |  76 +++++++
 drivers/acpi/device_pm.c                     |   3 +-
 drivers/base/power/Makefile                  |   2 +-
 drivers/base/power/power.h                   |   9 +
 drivers/base/power/wakeup.c                  |  59 +++---
 drivers/base/power/wakeup_stats.c            | 203 +++++++++++++++++++
 fs/eventpoll.c                               |   4 +-
 include/linux/pm_wakeup.h                    |  21 +-
 kernel/power/autosleep.c                     |   2 +-
 kernel/power/wakelock.c                      |  32 +--
 kernel/time/alarmtimer.c                     |   2 +-
 11 files changed, 358 insertions(+), 55 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-wakeup
 create mode 100644 drivers/base/power/wakeup_stats.c

v2:
- Updated Documentation/ABI/, as per Greg.
- Removed locks in attribute functions, as per Greg.
- Lifetimes of struct wakelock and struck wakeup_source are now different due to
  the latter embedding a refcounted kobject. Changed it so that struct wakelock
  only has a pointer to struct wakeup_source, instead of embedding it.
- Added CONFIG_PM_SLEEP_STATS that enables/disables wakeup source statistics in
  sysfs.

v3:
Changes by Greg:
- Reworked code to use 'struct device' instead of raw kobjects.
- Updated documentation file.
- Only link wakeup_stats.o when CONFIG_PM_SLEEP_STATS is enabled.
Changes by Tri:
- Reverted changes to kernel/power/wakelock.c. 'struct device' hides kobject
  operations. So no need to handle lifetimes in wakelock.c

v4:
- Added 'Co-developed-by:' and 'Tested-by:' fields to commit message.
- Moved new documentation to a separate file
  Documentation/ABI/testing/sysfs-class-wakeup, as per Greg.
- Fixed copyright header in drivers/base/power/wakeup_stats.c, as per Greg.

v5:
- Removed CONFIG_PM_SLEEP_STATS
- Used PTR_ERR_OR_ZERO instead of if(IS_ERR(...)) + PTR_ERR, reported by
  kbuild test robot <lkp@intel.com>
- Stephen reported that a call to device_init_wakeup() and writing 'enabled' to
  that device's power/wakeup file results in multiple wakeup source being
  allocated for that device.  Changed device_wakeup_enable() to check if device
  wakeup was previously enabled.
Changes by Stephen:
- Changed stats location from /sys/class/wakeup/<name>/* to
  /sys/class/wakeup/wakeup<ID>/*, where ID is an IDA-allocated integer. This
  avoids name collisions in /sys/class/wakeup/ directory.
- Added a "name" attribute to wakeup sources, and updated documentation.
- Device registering the wakeup source is now the parent of the wakeup source.
  Updated wakeup_source_register()'s signature and its callers accordingly.

v6:
- Changed stats location to /sys/class/wakeup/ws<ID>/*
- Replaced ida_simple_get()/ida_simple_remove() with ida_alloc()/ida_free() as
  the former is deprecated.
- Reverted changes to device_init_wakeup(). Rafael is preparing a patch to deal
  with extra wakeup source allocation in a separate patch.

v7:
- Removed wakeup_source_init(), wakeup_source_prepare().
- Removed duplicate wakeup source creation code from  kernel/power/wakelock.
- Moved ID allocation to wakeup source object creation time.
- Changed stats location back to /sys/class/wakeup/wakeup<ID>/*
- Remove wakeup source device's "power" attributes.

v8:
- Updated commit message on patch 1 to indicate change of behavior of
  wakeup_source_create(), as per Stephen.
- Included headers for used symbols, as per Stephen.
- Added a function to create wakeup source devices to use
  device_set_pm_not_required() to skip power management for such devices, as per
  Stephen.

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2.22.0.770.g0f2c4a37fd-goog