port-amd64/52493: NetBSD boot freezes on xhci_init on Mac Mini (MGEN2AE/A)

[vezhlys%gmail.com@localhost]

>Number:         52493
>Category:       port-amd64
>Synopsis:       NetBSD boot freezes on xhci_init on Mac Mini (MGEN2AE/A)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Aug 20 18:35:00 +0000 2017
>Originator:     Andrius V
>Release:        NetBSD 8.0_BETA
>Organization:
>Environment:
>Description:
Recently I performed some NetBSD 8 testing on various hardware including Mac Mini (MGEN2AE/A). The problem I encountered in booting it on this system was that it just freezes without any error message. After some trial and error I found that the freeze occurs on xhci_init, specifically on this line (xhci.c line 1180):

xhci_op_write_4(sc, XHCI_USBCMD, XHCI_CMD_INTE|XHCI_CMD_RS); /* Go! */

Commenting out the line and rebuilding the kernel actually allows system to boot (of course, USB3 fails to work but at least system boot doesn't freeze). Unfortunately my knowledge stops here though I can try to get more info if needed.

Ideally it would be nice to make USB3 work (as mac mini is quite useless without USB) but I believe at least the freeze shouldn't occur on the boot. 

Debug messages from boot for xhci (with commented out line above):

...
xhci0 at pci0 dev 20 function 0: vendor 8086 product 9c31 (rev. 0x04)
xhci0: interrupting at msi2 vec 0
xhci0: xHCI version 1.0
xhci0: hcs1=d000820 hcs2=84000054 hcs3=200000a
xhci0: hcc=0x200077c1<XECP=0x2000,MAXPSA=0x7,SEC,SPC,PAE,NSS,LTC,AC64>
xhci0: xECP 8000
xhci0: ECR: 0x02000802
xhci0:  SP: 02000802 20425355 30180901 00000000
xhci0:  hs ports 1 - 9
xhci0: ECR: 0x03000802
xhci0:  SP: 03000802 20425355 1000040a 00000000
xhci0:  ss ports 10 - 13
xhci0: ECR: 0x00010cc1
xhci0: ECR: 0x0000fcc0
xhci0: ECR: 0x00000801
xhci0: ECR: 0x0005000a
xhci0: PAGESIZE 0x00000001
xhci0: sc_pgsz 0x00001000
xhci0: sc_maxslots 0x00000020
xhci0: sc_maxports 13
xhci0: sc_maxspbuf 16
xhci0: eventst: 000000010f414fc0 0xffff80008e5c7fc0 1000
xhci0: dcbaa: 000000010f415000 0xffff80008e5c8000 1000
xhci0: current IMOD 1000
xhci0: USBCMD 00000000
xhci0: USB3PRM / USB3.0 configurable ports: 0x0000000f
xhci0: USB3_PSSEN / Enabled USB3.0 ports under xHCI: 0x0000000f
xhci0: XUSB2PRM / USB2.0 ports can switch from EHCI to xHCI:0x000001ff
xhci0: XUSB2PR / USB2.0 ports under xHCI: 0x000001ff
usb0 at xhci0: USB revision 3.0
usb0: WARNING: power management not supported
usb1 at xhci0: USB revision 2.0
usb1: WARNING: power management not supported
...
uhub0 at usb0: vendor 8086 (0x8086) xHCI Root Hub (0000), class 9/0, rev 1.00/1.00, addr 0
uhub0: 4 ports with 4 removable, self powered
uhub1 at usb1: vendor 8086 (0x8086) xHCI Root Hub (0000), class 9/0, rev 2.00/1.00, addr 0
uhub1: 9 ports with 9 removable, self powered
...
uhub1: device problem, disabling port 1
uhub1: device problem, disabling port 2
uhub1: device problem, disabling port 3
uhub1: device problem, disabling port 4
>How-To-Repeat:

>Fix: