On Wed, 4 Sep 2013, Catalin Marinas wrote:
I have yet to see the value of MCPM on top of a PSCI back-end, other than allowing people to implement MCPM back-ends with non-standard EL3 calls (but happy to be proven wrong).
That's certainly a valid case. PSCI is very abstract and some people don't want to put all the power management complexity into firmware.
For cases where EL3 is not present (and PSCI not easily possible), I can accept MCPM but I would rather use it as a library driven from SoC-specific power code (e.g. under drivers/cpuidle/) rather than MCPM being the front-end to any CPU power management.
I disagree. If experience has tought us something is that you cannot have power management into cpuidle, and then have power management for CPU hotplug, and then have something else like IKS also wanting to have a say into power management, or kexec, etc. This turned out to be a complete unsolvable mess on TC2, which is the very reason why MCPM was created.
At some point you need a central place where concurrent and sometimes conflicting requests are arbitrated.
Nicolas