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

11 This is a HOWTO for using the USB3 debug port on x86 systems.
19 	3) have a USB 3.0 super-speed A-to-A debugging cable.
28 When DbC is initialized and enabled, it will present a debug
30 super-speed port). The debug device is fully compliant with
31 the USB framework and provides the equivalent of a very high
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-
44 On the debug target system, you need to customize a debugging
51 append a host contoller index to this kernel parameter. This
56 USB subsystem by adding below kernel boot parameter::
58 	"usbcore.autosuspend=-1"
61 port to a USB port (root port or port of any external hub) on
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
105 The DbC support has been added to the xHCI driver. You can get a
109 configured to support USB_XHCI_DBGCAP. A sysfs attribute under
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