u-boot not discovering USB storage devices

I have a USB flash drive that shows up fine under Linux, but under u-boot I get:

U-Boot# usb start
(Re)start USB…
USB0: Register 2000140 NbrPorts 2
Starting the controller
USB XHCI 1.00
scanning bus 0 for devices… cannot reset port 1!?
2 USB Device(s) found
scanning usb for storage devices… 0 Storage Device(s) found

Before I post to the u-boot list or look too much at the problem, I’m wondering if anyone already knows anything about this issue.

Aside: when attempting to use /dev/sda1 as the rootfs, the Debian initrd seems to prevent the kernel from discovering the USB device. When booting from uSD, everything works fine [1], but when I switch ‘mmcroot’ to ‘/dev/sda1 ro rootwait’ then USB is never found [2].

[1] http://pastebin.com/CAGB64i8
[2] http://pastebin.com/maxAqZTZ

I have a USB flash drive that shows up fine under Linux, but under u-boot I
get:

U-Boot# usb start
(Re)start USB...
USB0: Register 2000140 NbrPorts 2
Starting the controller
USB XHCI 1.00
scanning bus 0 for devices... cannot reset port 1!?
2 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found

Before I post to the u-boot list or look too much at the problem, I'm wondering
if anyone already knows anything about this issue.

Aside: when attempting to use /dev/sda1 as the rootfs, the Debian initrd seems
to prevent the kernel from discovering the USB device. When booting from uSD,
everything works fine [1], but when I switch 'mmcroot' to '/dev/sda1 ro
rootwait' then USB is never found [2].

[1] U-Boot SPL 2015.01-00001-g1f3008d (Jan 12 2015 - 17:12:46)DRA752 ES1.1U- - Pastebin.com

This shows the xhci controller finding the hub and the two devices
attached to it.

[2] [ 0.000000] Booting Linux on physical CPU 0x0[ 0.000000] Initializing cg - Pastebin.com

This doesn't show any xhci controller at all. I don't know what
mmcroot is, but are you sure that the xhci controller is in the system
image there vs. in the uSD? Can we see the full log from [2], there's a
bunch missing in the boot process that might give us a clue.

thanks,

greg k-h