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.
13 Before using any kernel debugging functionality based on USB3
16 	1) check whether any USB3 debug port is available in
19 	3) have a USB 3.0 super-speed A-to-A debugging cable.
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
41 Other uses include simpler, lockless logging instead of a full-
58 	"usbcore.autosuspend=-1"
63 should be a USB 3.0 super-speed A-to-A debugging cable.
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
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