Pinebook Pro instability problem and fix.

[Søren Schmidt]

Hi gang!

I have been wrestling my Pinebook Pro instability problem for some time.
The problem was that if I just let it boot it would occasionally hang silently, just lock up totally unresponsive, if I changed the clock speed it would run stable.
I finally figured out the problem and its actually quite simple.
On boot we set all the regulators initially to their lowest possible voltage, this in my case is too low to make the little cpu’s run reliably.
U-boot sets the lcpu voltage to 900mv and speed to 816Mhz, on boot we re-adjust the voltage to 750mv which is too low for my cpus to work reliably @ 816Mhz.
I’ve added support for the regulator-init-microvolt setting and set that to 900000mv as per spec in the DTS, and that solves the issue.
Now running all 6 cores with changeable frequencies and no problems what so ever.

Patches on request if needed…

-Søren