[coreboot] EHCI issue in APU3 (APU2) board

[Kamil]

Hi everybody,

We're trying to enable the USB on the J13 connector on APU3 board. It's using
the EHCI1 device (ports 0 to 3). As far as I understand it, USB controllers are
configured and set by the AGESA PI binary. I've tried with both versions of
AGESA - the one specific for pcengines boards (`3rdparty/blobs/mainboard/pcengines/apu2/AGESA.bin`)
and the latest one for this kind of chip (`3rdparty/blobs/pi/amd/00730F01/FT3b/AGESA.bin`).
Both versions deliver the same results. I've managed to use the latter version
by enabling all devices in `mainboard/pcengines/apu2/devicetree.cb`.
I'm using the master branch of coreboot, but also I've tried with some older
versions (same issue).

We're working on mainlining all the changes needed for APU3 and one of them is
this USB header. It's unconnected and not used on APU2 boards, so disabled by
default. Besides that, shouldn't have more changes in this area. APU3 is similar
to APU2 board (the same SOC and design in general). The USB connections are on
page 6 on the schematics.

My question is, what can we look for to investigate this issue further? Right
now we're out of options and we don't know what to do next. We would be grateful
for any insights on this matter.

* Schematics for APU2 board: https://pcengines.ch/schema/apu2c.pdf
* Schematics for APU3 board: https://pcengines.ch/schema/apu3a.pdf
* Diff of my changes: http://pastebin.com/8YKkzB7Z
* Boot log: http://pastebin.com/uBAubrz9
* PCI config space dumps: http://pastebin.com/3aBrt6wp
* lsusb dump: http://pastebin.com/V7NTWAnq

-- 
Best regards,
Kamil Wcisło
Embedded Systems Engineer
http://3mdeb.com | @3mdeb_com