[PATCH v2 0/7] Add thermal thresholds support

[Daniel Lezcano <daniel.lezcano@linaro.org>]

The trip points are a firmware description of the temperature limits
of a specific thermal zone where we associate an action which is done
by the kernel. The time resolution is low.

The userspace has to deal with a more complex thermal management based
on heuristics from different information coming from different
places. The logic is much more complex but based on a bigger time
resolution, usually one second based.

The purpose of the userspace is to monitor the temperatures from
different places and take actions. However, it can not be constantly
reading the temperature to detect when a temperature threshold has
been reached. This is especially bad for mobile or embedded system as
that will lead to an unacceptable number of wakeup to check the
temperature with nothing to do.

On the other side, the sensors are now most of the time interrupt
driven. That means the thermal framework will use the temperature trip
points to program the sensor to trigger an interrupt when a
temperature limit is crossed.

Unfortunately, the userspace can not benefit this feature and current
solutions found here and there, iow out-of-tree, are to add fake trip
points in the firmware and enable the writable trip points.

This is bad for different reasons, the trip points are for in-kernel
actions, the semantic of their types is used by the thermal framework
and by adding trip points in the device tree is a way to overcome the
current limitation but tampering with how the thermal framework is
supposed to work. The writable trip points is a way to adjust a
temperature limit given a specific platform if the firmware is not
accurate enough and TBH it is more a debug feature from my POV.

The thresholds mechanism is a way to have the userspace to tell
thermal framework to send a notification when a temperature limit is
crossed. There is no id, no hysteresis, just the temperature and the
direction of the limit crossing. That means we can be notified when a
threshold is crossed the way up only, or the way down only or both
ways. That allows to create hysteresis values if it is needed.

A threshold can be added, deleted or flushed. The latter means all
thresholds belonging to a thermal zone will be deleted.
    
When a threshold is added:

 - if the same threshold (temperature and direction) exists, an error
   is returned

 - if a threshold is specified with the same temperature but a
   different direction, the specified direction is added

 - if there is no threshold with the same temperature then it is
   created

When a threshold is deleted:

 - if the same threshold (temperature and direction) exists, it is
   deleted

 - if a threshold is specified with the same temperature but a
   different direction, the specified direction is removed

 - if there is no threshold with the same temperature, then an error
   is returned

When the threshold are flushed:

 - All thresholds related to a thermal zone are deleted

When a threshold is crossed:

 - the userspace does not need to know which threshold(s) have been
   crossed, it will be notified with the thermal zone identifier, the
   current temperature and the previous temperature

 - if multiple thresholds have been crossed between two updates only
   one notification will be send to the userspace, it is pointless to
   send a notification per thresholds crossed as the userspace can
   handle that easily when it has the temperature delta information

All aforementioned actions and events lead to a notification to the
userspace. A threshold change (add, delete and flush) is notified to
the userspace with the process id responsible of the action.

Along with the kernel changes, the thermal library has been extended
to provide the different API to deal with the new threshold netlink
events and commands.

In addition, the thermal-engine skeleton uses these new API by
flushing and adding thresholds as well as getting the notification
about these actions.

Overall the series has been tested with the thermal-engine skeleton
and some selftests which are not part of this series.

Changelog:
  V2:
    - Compute min and max in thermal_zone_device_update() but keep
      the loop as it is (Rafael)

    - Include slab.h to fix compilation warnings on some architectures
      with kmalloc and kfree (kernel test robot)

Daniel Lezcano (7):
  thermal/core: Compute low and high boundaries in
    thermal_zone_device_update()
  thermal/core: Add thresholds support
  thermal/core: Connect the threshold with the core
  thermal/netlink: Add the commands and the events for the thresholds
  tools/lib/thermal: Make more generic the command encoding function
  tools/lib/thermal: Add the threshold netlink ABI
  tools/thermal/thermal-engine: Take into account the thresholds API

 drivers/thermal/Kconfig                       |  15 ++
 drivers/thermal/Makefile                      |   3 +
 drivers/thermal/thermal_core.c                |  21 +-
 drivers/thermal/thermal_core.h                |   6 +-
 drivers/thermal/thermal_netlink.c             | 239 ++++++++++++++++-
 drivers/thermal/thermal_netlink.h             |   7 +
 drivers/thermal/thermal_thresholds.c          | 247 ++++++++++++++++++
 drivers/thermal/thermal_thresholds.h          |  54 ++++
 drivers/thermal/thermal_trip.c                |  27 +-
 include/linux/thermal.h                       |   3 +
 include/uapi/linux/thermal.h                  |  30 ++-
 tools/lib/thermal/commands.c                  | 167 +++++++++++-
 tools/lib/thermal/events.c                    |  58 +++-
 tools/lib/thermal/include/thermal.h           |  40 +++
 tools/lib/thermal/libthermal.map              |   5 +
 tools/lib/thermal/thermal.c                   |  17 ++
 tools/thermal/lib/Makefile                    |   2 +-
 tools/thermal/thermal-engine/thermal-engine.c | 109 +++++++-
 18 files changed, 972 insertions(+), 78 deletions(-)
 create mode 100644 drivers/thermal/thermal_thresholds.c
 create mode 100644 drivers/thermal/thermal_thresholds.h

-- 
2.43.0