On Tue, 25 Oct 2016, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote: > Add Documentation/usb/usb3-debug-port.txt. This document includes > the user guide for USB3 debug port. It's in reStructuredText, please name it .rst. Thanks, Jani. > > Cc: linux-doc@xxxxxxxxxxxxxxx > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> > --- > Documentation/usb/usb3-debug-port.txt | 89 +++++++++++++++++++++++++++++++++++ > 1 file changed, 89 insertions(+) > create mode 100644 Documentation/usb/usb3-debug-port.txt > > diff --git a/Documentation/usb/usb3-debug-port.txt b/Documentation/usb/usb3-debug-port.txt > new file mode 100644 > index 0000000..29ebbf4 > --- /dev/null > +++ b/Documentation/usb/usb3-debug-port.txt > @@ -0,0 +1,89 @@ > +=============== > +USB3 debug port > +=============== > + > +:Author: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> > +:Date: October 2016 > + > +GENERAL > +======= > + > +This is a HOWTO for using USB3 debug port on x86 systems. > + > +Before using any kernel debugging functionalities based on USB3 > +debug port, you need to check 1) whether debug port is supported > +by the xHCI host, 2) which port is used for debugging purpose > +(normally the first USB3 root port). You must have a USB 3.0 > +super-speed A-to-A debugging cable to connect the debug target > +with a debug host. In this document, a debug target stands for > +the system under debugging; while, a debug host stands for a > +stand-alone system that is able to talk to the debugging target > +through the USB3 debug port. > + > +EARLY PRINTK > +============ > + > +On debug target system, you need to customize a debugging kernel > +with CONFIG_EARLY_PRINTK_XDBC enabled. And add below kernel boot > +parameter:: > + > + "earlyprintk=xdbc" > + > +If there are multiple xHCI controllers in the system, you can > +append a host contoller index to this kernel parameter. This > +index is started from 0. > + > +If you are going to leverage the keep option defined by the > +early printk framework to keep the boot console alive after > +early boot, you'd better add below kernel boot parameter:: > + > + "usbcore.autosuspend=-1" > + > +On debug host side, you don't need to customize the kernel, but > +you need to disable usb subsystem runtime power management by > +adding below kernel boot parameter:: > + > + "usbcore.autosuspend=-1" > + > +Before starting the debug target, you should connect the debug > +port on debug target with a root port or port of any external hub > +on the debug host. The cable used to connect these two ports > +should be a USB 3.0 super-speed A-to-A debugging cable. > + > +During early boot of debug target, DbC (the debug engine for USB3 > +debug port) hardware gets initialized. Debug host should be able > +to enumerate the debug target as a debug device. Debug host will > +then bind the debug device with the usb_debug driver module and > +create the /dev/ttyUSB0 device. > + > +If device enumeration goes smoothly, you should be able to see > +below kernel messages on debug host:: > + > + # tail -f /var/log/kern.log > + [ 1815.983374] usb 4-3: new SuperSpeed USB device number 4 using xhci_hcd > + [ 1815.999595] usb 4-3: LPM exit latency is zeroed, disabling LPM. > + [ 1815.999899] usb 4-3: New USB device found, idVendor=1d6b, idProduct=0004 > + [ 1815.999902] usb 4-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3 > + [ 1815.999903] usb 4-3: Product: Remote GDB > + [ 1815.999904] usb 4-3: Manufacturer: Linux > + [ 1815.999905] usb 4-3: SerialNumber: 0001 > + [ 1816.000240] usb_debug 4-3:1.0: xhci_dbc converter detected > + [ 1816.000360] usb 4-3: xhci_dbc converter now attached to ttyUSB0 > + > +You can run below bash scripts on debug host to read the kernel > +log sent from debug target. > + > +.. code-block:: sh > + > + ===== start of bash scripts ============= > + #!/bin/bash > + > + while true ; do > + while [ ! -d /sys/class/tty/ttyUSB0 ] ; do > + : > + done > + cat /dev/ttyUSB0 >> xdbc.log > + done > + ===== end of bash scripts =============== > + > +You should be able to see the early boot message in xdbc.log. -- Jani Nikula, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
