The purpose of this page is document how to enable basic CPU Idle on Renesas platforms (RCar-H2 being the primary target). CPUIdle is a standard Linux power management framework aimed at reducing CPU power consumption when it is idle.

• CPUIdle support is done on the CA7 cluster only. CA15 cluster is out of the scope. Also, as the CA7 CPU core wakeup through arch timer is not 100% functional on this platform, CMT timer was used for the purpose of this prototype.
• Trying to use the the arch timer will stuck the scheduler due to the lack of working wakeup events for the CA7.

  Note: Disabling arch timer here will probably have an impact on all
  the other SH platforms supported in multiplatform config.
  A "smarter" approach, i.e dynamic, will have to be used if the arch
  timer cannot be fixed.

The patches to enable CPUIdle for the CA7 cluster are available here.

1. ARM: shmobile: cpuidle: Add a C1 state for "core standby"
2. ARM: shmobile: lager: Enable CPU idle
3. ARM: shmobile: Enable CPU idle for multiplatform

All these changes are available in this http://git.baylibre.com/pub/bcousson/linux-sh/log/?h=cpuidle.

  Note: The target_residency and exit_latency will have to be refined
  based on power measurement and performance impact on differents
  key use cases.

Power measurement with and without CPUIlde enabled:

TBD. Doing accurate measurement will require modifying the Lager board as explained here : Enabling Power Measurements on Renesas H2 Lager Board

First results will be posted as soon as the board is modified.