Base firmware interface to clock/power/perfomance functionalty on the SCMI spec

[vianpl]

The spec I refer to [1] is provided by ARM and covers the problematic we have on the RPi: the firmware controls the clocking, power and performance yet doesn't provide a "full" interface to the operating system.

The benefits would be:

• Out of the box kernel support, as ARM did all of the work already.
• Less kernel maintenance for everyone.
• Well thought interface with firmware for free (I assume it's free, I might be wrong on that one).
• Not too big for a spec, 80 pages.

The possible downsides:

• See how this integrates with bcm2835 platform code & device tree.

Note that I haven't read the spec in depth, and some other downsides could arise. But I thought it's worth commenting it. 😃

[1] http://infocenter.arm.com/help/topic/com.arm.doc.den0056a/DEN0056A_System_Control_and_Management_Interface.pdf

[ptesarik]

This could be implemented as a new VCHIQ service (using the 'SCMI' fourcc).