USB3 superspeed does not work on xperia xz2 running sailfishos-sony-tama

The usb-c port on xperia xz2 has usb3 capability, even its sony flash and fastboot mode support usb3 superspeed (5000M, observable with `lsusb -t`), but all mode sailfishos-sony-tama provides (developer mode, mtp, charging) only works on usb2 highspeed (480M). It should not be a hardware issue, since I can use the same cable on superspeed when using sony flash and fastboot mode.