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>
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@ -98,3 +98,55 @@ you to check the sanity of the setup.
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cat /dev/ttyUSB0
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cat /dev/ttyUSB0
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done
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done
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===== end of bash scripts ===============
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===== end of bash scripts ===============
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Serial TTY
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==========
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The DbC support has been added to the xHCI driver. You can get a
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debug device provided by the DbC at runtime.
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In order to use this, you need to make sure your kernel has been
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configured to support USB_XHCI_DBGCAP. A sysfs attribute under
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the xHCI device node is used to enable or disable DbC. By default,
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DbC is disabled::
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root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
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disabled
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Enable DbC with the following command::
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root@target:/sys/bus/pci/devices/0000:00:14.0# echo enable > dbc
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You can check the DbC state at anytime::
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root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
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enabled
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Connect the debug target to the debug host with a USB 3.0 super-
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speed A-to-A debugging cable. You can see /dev/ttyDBC0 created
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on the debug target. You will see below kernel message lines::
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root@target: tail -f /var/log/kern.log
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[ 182.730103] xhci_hcd 0000:00:14.0: DbC connected
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[ 191.169420] xhci_hcd 0000:00:14.0: DbC configured
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[ 191.169597] xhci_hcd 0000:00:14.0: DbC now attached to /dev/ttyDBC0
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Accordingly, the DbC state has been brought up to::
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root@target:/sys/bus/pci/devices/0000:00:14.0# cat dbc
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configured
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On the debug host, you will see the debug device has been enumerated.
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You will see below kernel message lines::
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root@host: tail -f /var/log/kern.log
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[ 79.454780] usb 2-2.1: new SuperSpeed USB device number 3 using xhci_hcd
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[ 79.475003] usb 2-2.1: LPM exit latency is zeroed, disabling LPM.
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[ 79.475389] usb 2-2.1: New USB device found, idVendor=1d6b, idProduct=0010
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[ 79.475390] usb 2-2.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
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[ 79.475391] usb 2-2.1: Product: Linux USB Debug Target
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[ 79.475392] usb 2-2.1: Manufacturer: Linux Foundation
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[ 79.475393] usb 2-2.1: SerialNumber: 0001
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The debug device works now. You can use any communication or debugging
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program to talk between the host and the target.
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