RFC drivers/thermal: support for multiple TZ for sensor

This is an attempt at introducing multiple thermal zones for each thermal sensor. The usecase behind this is that, a sensor may involved in monitoring a region that could have different mitigative actions. For example, a sensor placed between audio and camera IP, will involve different mitigative actions on these blocks. Sometimes it is also desirable to employ different governors and different mitigative strategies for the same sensor. For example, using step-wise governor for temperatures > 0 and a userspace governor for temperatures < 0 degC.

The idea presented in this patchset involves linking thermal zones together that share the same underlying sensor. The sensor still interacts with one thermal zone that we deem as the primary thermal sensor. The low thresholds set on a sensor is the max of min thresholds for the high trip threshold while the low trip thresholds for the sensor is the min of max thresholds from the different thermal zones of the sensor around the current sensor temperature. When the sensor temperature crosses the threshold, the thermal zone is notified and the new thresholds is evaluated again.

These patches continue to return a struct thermal_zone * back to the sensor when the sensor registers. While this prevents breaking the existing interaction, it is not very clean and optimal. This is something to think about as we review the patches. The breakdown of the patches in this set is -

- Patch #1 refactors the current data structures to help with the new support
- Patch #2 allows probing and set up of multiple thermal zones when a sensor is registered.
- Patch #3 aggregates across multiple thermal zones to figure out the mitigation and set new thresholds on the sensor. Sensor low and high thresholds are set based on thresholds from any thermal zone of the sensor.
- Patch #4 notifies the framework and the related thermal zones when the sensor is tripped

Please consider reviewing these patches. We have seen benefits of this idea and is implemented and used in mobile products.

Lina Iyer (4):
drivers: of-thermal: abstract sensor related information
drivers: of-thermal: allow multiple thermal zones for a sensor
drivers: of-thermal: aggregate sensor trips across thermal zones
drivers: of-thermal: notify framework when sensor is tripped

 drivers/thermal/of-thermal.c      | 205 ++++++++++++++++++++++++++----
 drivers/thermal/thermal_helpers.c |  37 +++---
 include/linux/thermal.h           |  10 ++
 3 files changed, 209 insertions(+), 43 deletions(-)

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