This is a good question. I trying almost the same with two of JMicron JMS551 SATA3 dual port docking station with four SATA HDD. Two HDD on both USB3-A and USB3-C ports. I use Arch linux with Mainline kernel (4.20.3-1-ARCH) and a little trick was needed to get USB-C to work as it is in OTG mode by default and needed to change to host mode:
"fdtput -t s /boot/dtbs/rockchip/rk3399-rockpro64.dtb /usb@fe800000/dwc3 dr_mode host"
After reboot the second docking station is working but it is not USB3 but USB2 (Bus #5):
[oreggin@nas ~]$ lsusb -t
/: Bus 08.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 5000M
|__ Port 1: Dev 2, If 0, Class=Mass Storage, Driver=uas, 5000M
/: Bus 07.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 480M
/: Bus 06.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 5000M
/: Bus 05.Port 1: Dev 1, Class=root_hub, Driver=xhci-hcd/1p, 480M
|__ Port 1: Dev 2, If 0, Class=Mass Storage, Driver=uas, 480M
/: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=ohci-platform/1p, 12M
/: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=ohci-platform/1p, 12M
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-platform/1p, 480M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-platform/1p, 480M
[oreggin@nas ~]$
I use this cable between RockPro64 USB-C port and docking station USB3-B port:
https://www.conrad.com/ce/en/product/142...connectors
Any idea how to make it work in USB3 mode?
Thanks!