access usb disk in uboot

Hi, I want to access usb disk in uboot.
but in uboot on nano:

Tegra210 (P3450-Porg) # usb start
starting USB...
USB0:   tegrausb: Invalid dr_mode 2 for host mode
probe failed, error -1
USB error: all controllers failed lowlevel init

then I try uboot on TX1:

Tegra210 (P2371-2180) # usb start
starting USB...
USB0:   USB EHCI 1.10
scanning bus 0 for devices... EHCI timed out on TD - token=0x80008c80
2 USB Device(s) found

it’s ok.

I read L4T document Driver package -> Software Features -> Boot Loaders -> U-Boot

Nano:
U-Boot Storage Device Support  SKU 0000: SD Card, NFS
                               SKU 0020: eMMC, SD Card
TX1:
U-Boot Storage Device Support  eMMC (no CQ), SD card, USB (HS)

Does it mean that USB is not supported in uboot on nano?
In this case, how should I do to access usb disk in uboot on nano?

Thanks!

Currently, due to driver of XHCI not ready on u-boot, this is not yet supported.