A true mainline Linux Kernel for the Pinebook Pro

[tsys]

@tsys, Do you happen to know if the DP Alt-mode over USB-C is using 2 or 4 lanes?

If I understand DP Alt-mode correctly, (and it's possible I don't :-), if we use 2 lanes for DP, we can use the other 2 lanes for USB 3. This would allow some of the USB-C docks to have both video from the Pinebook Pro, (not USB device video), And USB 3 peripherals like Gigabit Ethernet and more USB 3 ports via a hub.

A drawback to using DP Alt-mode over 2 lanes is that it would limit the resolution or refresh rate. So it's a choice the user would have to make. Use a simple 4 lane DP Alt-mode to video adapter, (I have one that works), and use Pinebook Pro's other USB 3 port for any higher speed peripherals.

I think the Pinebook Pro hardware should support Pin assignments C, D and E. Of those only mode D supports DP + USB. Since the rk3399 supports 4k@60HZ with DP 1.2 it must be using 4 lanes in mode C and/or E. I've added software support for all of the modes but sadly I'm missing a dock to test the USB mode. I've just ordered a cheap dock with DP altmode and one superspeed USB port so I can do some testing. Will get that in a few days.