Date:   Thu, 20 Oct 2016 11:30:54 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, linux-usb@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [RESEND PATCH v2 4/4] usb: doc: add document for USB3 debug port usage

On Thu, 20 Oct 2016, Lu Baolu <baolu.lu@...ux.intel.com> wrote:
> Hi Jani,
>
> On 10/19/2016 03:48 PM, Jani Nikula wrote:
>> On Wed, 19 Oct 2016, Lu Baolu <baolu.lu@...ux.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?

Read Documentation/kernel-documentation.rxt. Install Sphinx. Run 'make
htmldocs'.

BR,
Jani.


>
> Best regards,
> Lu Baolu
>
>>
>> BR,
>> Jani.
>>
>>> Cc: linux-doc@...r.kernel.org
>>> Signed-off-by: Lu Baolu <baolu.lu@...ux.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@...ux.intel.com>
>> :Author: Lu Baolu <baolu.lu@...ux.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.
>

-- 
Jani Nikula, Intel Open Source Technology Center

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