imx8mm USB Mass Storage fails through a HUB

[Tim Harvey]

Greetings,

I'm finding that USB Mass Storage devices appear to fail detection on
imx8mm when hanging off a USB hub whereas other devices such as USB
ethernet work fine.

u-boot=> usb start && usb tree
starting USB...
Bus usb at 32e40000: Bus usb at 32e50000: USB EHCI 1.00
scanning bus usb at 32e40000 for devices... 1 USB Device(s) found
scanning bus usb at 32e50000 for devices... cannot reset port 3!?
3 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found
USB device tree:
  1  Hub (480 Mb/s, 0mA)
     u-boot EHCI Host Controller

  1  Hub (480 Mb/s, 0mA)
  |  u-boot EHCI Host Controller
  |
  +-2  Hub (480 Mb/s, 0mA)
    |  Microchip Tech USB2744
    |
    +-3  Vendor specific (480 Mb/s, 0mA)
         Microchip Tech Hub Controller

Depending on the board and port sometimes I see the 'cannot reset
port' issue calling out the port of the hub and sometimes I see a
'EHCI timed out on TD - token=0x80008c80 unable to get device
descriptor (error=-1)' error.

I have several imx8m{m,n,p}-venice boards with onboard hubs I noticed
this with but you can re-create this on an imx8mm-evk if you attach a
HUB with a USB Mass Storage Device to the front-panel USB Type-C
connector after manually enabling VBUS (due to the lack of a PTN5110
driver that would handle source/sink detection on that port):
i2c dev 1 && i2c mw 0x50 0x23 0x77 1 # COMMAND: SRC_VBUS_HIGH
usb start && usb tree

So far I've tried without success:
- setenv usb_pgood_delay 5000
- CONFIG_USB_ONBOARD_HUB=y

Any ideas on this?

Best Regards,

Tim