[PATCH v3 1/2] cpufreq: spacemit: Add K1 cpufreq driver

[Viresh Kumar]

Hi Shuwei,

On 15-06-26, 14:12, Shuwei Wu wrote:
> The clusters have separate clocks, but they share the same voltage supply.[1]
> So two independent policies would be unsafe: one policy could lower the shared
> voltage while the other cluster is still running at a higher frequency.

No, both will vote for the regulator contraints using CPU device and the
regulator core will make sure it doesn't break any of them. This is what all
frameworks do, regulator, clk, etc.

> This means they can't use different policies.

This is incorrect.

> From a hardware perspective, the eight cores of the K1 are homogeneous,
> so using the same policy for them is relatively reasonable.

Right, but this is inefficient. One cluster can be idle, or in low freq mode
while other can be in higher. They MUST be two policies.

> I used a K1-specific driver because cpufreq-dt only manages one CPU clock
> through the CPU device used for the OPP transition.
> On K1, the policy needs to control two independent cluster clocks and one shared
> regulator, so the driver has to update the second cluster clock explicitly and
> keep the ordering safe: raise voltage before raising either cluster, and lower
> both cluster clocks before lowering the shared voltage.
> 
> [1] https://lore.kernel.org/spacemit/aeaXszeaE62rM6BJ@aurel32.net/

-- 
viresh