tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
usb: doc: Update document for USB3 debug port usage
Update Documentation/driver-api/usb/usb3-debug-port.rst. This update
includes the guide for using xHCI debug capability based TTY serial
link.
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
authored by
Lu Baolu
and committed by
Jonathan Corbet
90b2a01e
481f2720
+52
+52
Documentation/driver-api/usb/usb3-debug-port.rst
+52
Documentation/driver-api/usb/usb3-debug-port.rst
···
98
98
cat /dev/ttyUSB0
99
99
done
100
100
===== end of bash scripts ===============
101
+
102
+
Serial TTY
103
+
==========
104
+
105
+
The DbC support has been added to the xHCI driver. You can get a
106
+
debug device provided by the DbC at runtime.
107
+
108
+
In order to use this, you need to make sure your kernel has been
109
+
configured to support USB_XHCI_DBGCAP. A sysfs attribute under
110
+
the xHCI device node is used to enable or disable DbC. By default,
111
+
DbC is disabled::
112
+
113
+
root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
114
+
disabled
115
+
116
+
Enable DbC with the following command::
117
+
118
+
root@target:/sys/bus/pci/devices/0000:00:14.0# echo enable > dbc
119
+
120
+
You can check the DbC state at anytime::
121
+
122
+
root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
123
+
enabled
124
+
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
127
+
on the debug target. You will see below kernel message lines::
128
+
129
+
root@target: tail -f /var/log/kern.log
130
+
[ 182.730103] xhci_hcd 0000:00:14.0: DbC connected
131
+
[ 191.169420] xhci_hcd 0000:00:14.0: DbC configured
132
+
[ 191.169597] xhci_hcd 0000:00:14.0: DbC now attached to /dev/ttyDBC0
133
+
134
+
Accordingly, the DbC state has been brought up to::
135
+
136
+
root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
137
+
configured
138
+
139
+
On the debug host, you will see the debug device has been enumerated.
140
+
You will see below kernel message lines::
141
+
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
150
+
151
+
The debug device works now. You can use any communication or debugging
152
+
program to talk between the host and the target.