So I have some displays that have their control boards and backlights powered by the USB.
If I plug the USB into the hikey960, and then power it on, the display only occasionally starts correctly. If I power the display externally, and then transfer the USB to the hikey960 after it has already started up, then it works.
This is incredibly inconvenient, since it also has a capacitive touch sensor.
What appears to be happening, is there is a switch on the USB power, which is only turned on by the kernel (or maybe bootloader) some time probably just before the display is initialized – not early enough for the control board to consistently set itself up to identify itself to the kernel.
I’ve already got video=HDMI-A-1:1280x800@60 kernel parameter. Its apparently not enough.