Re: [RESEND PATCH v2 4/4] usb: doc: add document for USB3 debug port usage

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Jani,

On 10/19/2016 03:48 PM, Jani Nikula wrote:
> On Wed, 19 Oct 2016, Lu Baolu <baolu.lu@linux.intel.com> wrote:
>> Add Documentation/usb/usb3-debug-port.txt. This document includes
>> the user guide for USB3 debug port.
> If you're adding completely new files, please at least consider writing
> them in reStructuredText, so we can easily bolt them to the Sphinx
> build. Just a few tweaks would be required, comments inline below.

Thanks for your comments. I will refactor my document according
to your comments.

By the way, are there any tools that I can use to check the document
format?

Best regards,
Lu Baolu

>
> BR,
> Jani.
>
>> Cc: linux-doc@vger.kernel.org
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>  Documentation/usb/usb3-debug-port.txt | 87 +++++++++++++++++++++++++++++++++++
>>  1 file changed, 87 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..df5ce27
>> --- /dev/null
>> +++ b/Documentation/usb/usb3-debug-port.txt
>> @@ -0,0 +1,87 @@
>> +                  USB3 debug port
> Make that a title with
>
> ===============
> USB3 debug port
> ===============
>
>> +
>> +         Lu Baolu <baolu.lu@linux.intel.com>
> :Author: Lu Baolu <baolu.lu@linux.intel.com>
>
> Although git blame will give a more accurate idea after the file's been
> edited by others.
>
>> +
>> +              Last-updated: October 2016
> :Date: October 2016
>
> Again, this is what git does.
>
>> +
>> +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.
> Add :: at the end of previous line to make the below indented block
> preformatted text. Ditto for the others.
>
>> +
>> +    "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.
> Again, add :: and indent the below lines by some spaces.
>
>> +
>> +# 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.
> Same here. Alternatively, if you do
>
> .. code-block:: sh
>
> and indent the block, you'll get syntax highlighting in the output.
>
>> +
>> +===== 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.