Update Documentation/driver-api/usb/usb3-debug-port.rst. This update includes the guide for using xHCI debug capability based TTY serial link. Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> --- Documentation/driver-api/usb/usb3-debug-port.rst | 68 ++++++++++++++++++++++++ 1 file changed, 68 insertions(+) diff --git a/Documentation/driver-api/usb/usb3-debug-port.rst b/Documentation/driver-api/usb/usb3-debug-port.rst index feb1a36..4ad4787 100644 --- a/Documentation/driver-api/usb/usb3-debug-port.rst +++ b/Documentation/driver-api/usb/usb3-debug-port.rst @@ -98,3 +98,71 @@ you to check the sanity of the setup. cat /dev/ttyUSB0 done ===== end of bash scripts =============== + +Serial TTY +========== + +DbC has also been designed for a serial TTY device at runtime. +One use of this is running a login service on the debug target. +Hence it can be remote accessed by the debug host. Another use +can probably be found in servers. It provides a peer-to-peer USB +link between two host-only machines. This provides a reasonable +out-of-band communication method between two servers. + +In order to use this, you need to make sure your kernel has been +configured to support USB_XHCI_DBGCAP. A sysfs attribute under +the xHCI device node is used to enable or disable DbC. By default, +DbC is disabled:: + + root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc + disabled + +Enable DbC with the following command:: + + root@target:/sys/bus/pci/devices/0000:00:14.0# echo enable > dbc + +You can check the DbC state at anytime:: + + root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc + enabled + +Connect the debug target to the debug host with a USB 3.0 super- +speed A-to-A debugging cable. You can see the /dev/ttyDBC0 created +on the debug target. You will see below kernel message lines:: + + root@target: tail -f /var/log/kern.log + [ 182.730103] xhci_hcd 0000:00:14.0: DbC connected + [ 191.169420] xhci_hcd 0000:00:14.0: DbC configured + [ 191.169597] xhci_hcd 0000:00:14.0: DbC now attached to /dev/ttyDBC0 + +Accordingly, the DbC state has been brought up to:: + + root@host:/sys/bus/pci/devices/0000:00:14.0# cat dbc + configured + +On the debug host, you will see the debug device has been enumerated. +You will see below kernel message lines:: + + root@host: tail -f /var/log/kern.log + [ 79.454780] usb 2-2.1: new SuperSpeed USB device number 3 using xhci_hcd + [ 79.475003] usb 2-2.1: LPM exit latency is zeroed, disabling LPM. + [ 79.475389] usb 2-2.1: New USB device found, idVendor=1d6b, idProduct=0004 + [ 79.475390] usb 2-2.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3 + [ 79.475391] usb 2-2.1: Product: Remote GDB + [ 79.475392] usb 2-2.1: Manufacturer: Linux + [ 79.475393] usb 2-2.1: SerialNumber: 0001 + [ 79.660368] usb_debug 2-2.1:1.0: xhci_dbc converter detected + [ 79.660439] usb 2-2.1: xhci_dbc converter now attached to ttyUSB0 + +You can simply verify whether it works by:: + + # On target side + root@target: echo "Hello world" > /dev/ttyDBC0 + + # On host side + root@host: cat /dev/ttyUSB0 + Hello world + + # vice versa + +You have a workable serial link over USB now. -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
