TL-MR3420-v2 boot usb rootfs

Hi. I have used usb storage like rootfs but without overlayfs. I build the kernel following the instructions but for ath79.
While loading:

[    5.383953] VFS: Cannot open root device "sda1" or unknown-block(0,0): error -6
[    5.391512] Please append a correct "root=" boot option; here are the available partitions:

Help me please.

Enabled CONFIG_USB_UHCI_HCD in the kernel, after that everything worked