[PATCH RFC] WIP: clk: Draft for BCM2835 ARM core frequency control

[Eric Anholt]

Stefan Wahren <stefan.wahren at i2se.com> writes:

> Disclaimer: DO NOT USE THIS UNTESTED CODE !!!
>
> This approach adds a new clock driver which controls the ARM core
> frequency via the mailbox interface. So the cpufreq-dt driver can
> operate via the common clock API.

I've tried to follow the logic in the FW related to clock management
again, and once again I'm going to admit defeat.  So here are a couple
of things I learned:

I suspect you're going to have a very restricted frequency range if you
don't send a SET_TURBO packet or have a turbo setting in config.txt
already.  (GET_TURBO returns that state).

Also, if GET_MAX_TEMPERATURE returns nonzero, that means there's a VPU
thread running that's polling the temp and voltage and will crank down
the voltage and ARM/V3D/CORE/ISP/SDRAM clocks when out of bounds.
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