[PATCH v3 0/1] arm64: dts: rockchip: rk3528: Add CPU frequency scaling support

[Chukun Pan]

By default, the CPUs on RK3528 operates at 1.5GHz. Add CPU frequency and
voltage mapping to the device tree to enable dynamic scaling via cpufreq.

The OPP values come from downstream 5.10 kernel, using a voltage close to
the actual frequency. Frequencies below 1200MHz have been removed as they
currently use the same voltage.

If we want the actual frequency to reach 2016MHz, the voltage
needs to reach 1.13V (+0.03V), not sure if it is safe.
The maximum opp-table voltage of downstream kernel is 1.1V.

Here are the test results using mhz [1] on Radxa E20C:

--------------------------------------
display frequency |  actual frequency
     1200MHz      |      1286MHz
     1416MHz      |      1430MHz
     1608MHz      |      1640MHz
     1800MHz      |      1804MHz
     2016MHz      |      1946MHz
--------------------------------------

[1] https://github.com/wtarreau/mhz.git

Changed from v3:
  Remove frequencies below 1200MHz

Changed from v2:
  Rename label opp-table-0 to opp-table-cpu
  Adjust the voltage used for 408MHz to 1200MHz

Chukun Pan (1):
  arm64: dts: rockchip: rk3528: Add CPU frequency scaling support

 arch/arm64/boot/dts/rockchip/rk3528.dtsi | 39 ++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

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2.25.1