Barebox version: 2020.07.0
Hardware: i.MX6 ULL with external Microchip USB Hub attached

I got a bug report that some newer USB memory sticks do not work with
barebox. While with barebox-2020.01 these devices are not recognized at all, in
barebox-2020.07 I get at least some warnings:

# usb
> usb: USB: scanning bus for devices...
> usb1: Bus 001 Device 001: ID 0000:0000 EHCI Host Controller
> usb1-0: Bus 001 Device 002: ID 0424:4916 USB4916
> ERROR: usb1-0-4: unable to get descriptor, error 80000000
> usb1-0-4: Bus 001 Device 003: ID 0424:2240 
> usb1-0-6: Bus 001 Device 004: ID 0424:494a USB2 Controller Hub
> ERROR: usb1-0-0: unable to get descriptor, error 80000000
> usb1-0-0: Bus 001 Device 005: ID 090c:3267 
> usb: 5 USB Device(s) found

Beside the USB memory stick, also one of the hub's internal 
devices is not recognized correctly. The full log output with
global.loglevel=7 is attached. The first error seems to appear
in line 233. The USB device descriptor cannot be read:

> usb1-0-4: usb_control_msg: request: 0x6, requesttype: 0x80, value 0x100 index 0x0 length 0x12
> imx-usb 2184200.usb@2184200.of: pipe=8c000483, buffer=8ffca7c0, length=18, req=8ff57580
> imx-usb 2184200.usb@2184200.of: (req=6 (0x6), type=128 (0x80), value=256 (0x100), index=0
> imx-usb 2184200.usb@2184200.of: dev=4, usbsts=0x40081, p[1]=0x18001205, p[2]=0x0


Under Linux (on the same device), the USB drives work without any noticeable problems:

Linux messages (v5.4):
> [  111.458582] 000: usb 1-1.1: new high-speed USB device number 5 using ci_hdrc
> [  111.613740] 000: usb 1-1.1: New USB device found, idVendor=090c, idProduct=3267, bcdDevice=11.00
> [  111.613763] 000: usb 1-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
> [  111.613777] 000: usb 1-1.1: Product: Flash Disk
> [  111.613784] 000: usb 1-1.1: Manufacturer: USB
> [  111.615642] 000: usb-storage 1-1.1:1.0: USB Mass Storage device detected

An usbmon capture for Linux is also attached (USB memory stick is plugged in at
about packet 99).

Any hints how I can debug this problem. I've almost now knowledge about USB...

regards
Christian