driver-api/usb/usb3-debug-port.rst

2 USB3 debug port
11 This is a HOWTO for using the USB3 debug port on x86 systems.
14 debug port, you need to::
16 	1) check whether any USB3 debug port is available in
18 	2) check which port is used for debugging purposes;
19 	3) have a USB 3.0 super-speed A-to-A debugging cable.
25 functionality provided by the xHCI host controller. The xHCI
29 device through the debug port (normally the first USB3
30 super-speed port). The debug device is fully compliant with
32 performance full-duplex serial link between the debug target
33 (the system under debugging) and a debug host.
41 Other uses include simpler, lockless logging instead of a full-
51 append a host controller index to this kernel parameter. This
58 	"usbcore.autosuspend=-1"
61 port to a USB port (root port or port of any external hub) on
62 the debug host. The cable used to connect these two ports
63 should be a USB 3.0 super-speed A-to-A debugging cable.
66 initialized. After initialization, the debug host should be able
67 to enumerate the debug device in debug target. The debug host
72 to see below kernel messages on the debug host::
74 	# tail -f /var/log/kern.log
75 	[ 1815.983374] usb 4-3: new SuperSpeed USB device number 4 using xhci_hcd
76 	[ 1815.999595] usb 4-3: LPM exit latency is zeroed, disabling LPM.
77 	[ 1815.999899] usb 4-3: New USB device found, idVendor=1d6b, idProduct=0004
78 	[ 1815.999902] usb 4-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
79 	[ 1815.999903] usb 4-3: Product: Remote GDB
80 	[ 1815.999904] usb 4-3: Manufacturer: Linux
81 	[ 1815.999905] usb 4-3: SerialNumber: 0001
82 	[ 1816.000240] usb_debug 4-3:1.0: xhci_dbc converter detected
83 	[ 1816.000360] usb 4-3: xhci_dbc converter now attached to ttyUSB0
89 .. code-block:: sh
95 		while [ ! -d /sys/class/tty/ttyUSB0 ] ; do
125 Connect the debug target to the debug host with a USB 3.0 super-
126 speed A-to-A debugging cable. You can see /dev/ttyDBC0 created
129 	root@target: tail -f /var/log/kern.log
139 On the debug host, you will see the debug device has been enumerated.
142 	root@host: tail -f /var/log/kern.log
143 	[   79.454780] usb 2-2.1: new SuperSpeed USB device number 3 using xhci_hcd
144 	[   79.475003] usb 2-2.1: LPM exit latency is zeroed, disabling LPM.
145 	[   79.475389] usb 2-2.1: New USB device found, idVendor=1d6b, idProduct=0010
146 	[   79.475390] usb 2-2.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
147 	[   79.475391] usb 2-2.1: Product: Linux USB Debug Target
148 	[   79.475392] usb 2-2.1: Manufacturer: Linux Foundation
149 	[   79.475393] usb 2-2.1: SerialNumber: 0001
152 program to talk between the host and the target.