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Date: Tue, 14 Feb 2017 15:20:24 +0800 From: Lu Baolu <baolu.lu@...ux.intel.com> To: Peter Chen <peter.chen@....com>, Peter Chen <hzpeterchen@...il.com> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...hat.com>, Mathias Nyman <mathias.nyman@...ux.intel.com>, "tglx@...utronix.de" <tglx@...utronix.de>, "peterz@...radead.org" <peterz@...radead.org>, "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org> Subject: Re: [PATCH v7 5/5] usb: doc: add document for USB3 debug port usage Hi, On 02/14/2017 02:13 PM, Peter Chen wrote: > >> On 02/14/2017 11:45 AM, Peter Chen wrote: >>> On Tue, Feb 14, 2017 at 10:27 AM, Lu Baolu <baolu.lu@...ux.intel.com> wrote: >>> >>>> Add Documentation/usb/usb3-debug-port.rst. This document includes the >>>> user guide for USB3 debug port. >>>> >>>> Cc: linux-doc@...r.kernel.org >>>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com> >>>> --- >>>> Documentation/usb/usb3-debug-port.rst | 98 >>>> ++++++++++++++++++++++++++++++ >>>> +++++ >>>> 1 file changed, 98 insertions(+) >>>> create mode 100644 Documentation/usb/usb3-debug-port.rst >>>> >>>> diff --git a/Documentation/usb/usb3-debug-port.rst >>>> b/Documentation/usb/usb3-debug-port.rst >>>> new file mode 100644 >>>> index 0000000..9eddb3a >>>> --- /dev/null >>>> +++ b/Documentation/usb/usb3-debug-port.rst >>>> @@ -0,0 +1,98 @@ >>>> +=============== >>>> +USB3 debug port >>>> +=============== >>>> + >>>> +:Author: Lu Baolu <baolu.lu@...ux.intel.com> >>>> +:Date: January 2017 >>>> + >>>> +GENERAL >>>> +======= >>>> + >>>> +This is a HOWTO for using USB3 debug port on x86 systems. >>>> + >>>> +Before using any kernel debugging functionality 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 purposes (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, "debug target" stands for the system under >>>> +debugging, and "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 the debug target system, you need to customize a debugging kernel >>>> +with CONFIG_EARLY_PRINTK_USB_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 starts >>>> +from 0. >>>> + >>>> +If you are going to use 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 the debug host side, you don't need to customize the kernel, but >>>> +you'd better disable usb subsystem runtime power management by >>>> +adding below kernel boot parameter:: >>>> + >>>> + "usbcore.autosuspend=-1" >>>> + >>>> >>> Just curious, why autosuspend needs to be disabled for this function? >> This implementation doesn't support suspend/resume yet. > > Why host side needs to disable it too? If host side runtime suspend/resume is enabled, it might ask the debug device to suspend. This will cause the debug device dead. The suspend/resume of the debug device depends on xhci driver. I will make it happen in separated patches with more tests. It's in my TODO list. Best regards, Lu Baolu
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