From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751794AbdBNElX (ORCPT ); Mon, 13 Feb 2017 23:41:23 -0500 Received: from mga02.intel.com ([134.134.136.20]:10294 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750943AbdBNElV (ORCPT ); Mon, 13 Feb 2017 23:41:21 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,159,1484035200"; d="scan'208";a="1126260939" Subject: Re: [PATCH v7 5/5] usb: doc: add document for USB3 debug port usage To: Peter Chen References: <1487039241-596-1-git-send-email-baolu.lu@linux.intel.com> <1487039241-596-6-git-send-email-baolu.lu@linux.intel.com> Cc: Greg Kroah-Hartman , Ingo Molnar , Mathias Nyman , tglx@linutronix.de, peterz@infradead.org, "linux-usb@vger.kernel.org" , x86@kernel.org, lkml , linux-doc@vger.kernel.org From: Lu Baolu Message-ID: <58A28A6E.3030303@linux.intel.com> Date: Tue, 14 Feb 2017 12:41:18 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 02/14/2017 11:45 AM, Peter Chen wrote: > On Tue, Feb 14, 2017 at 10:27 AM, Lu Baolu wrote: > >> Add Documentation/usb/usb3-debug-port.rst. This document includes >> the user guide for USB3 debug port. >> >> Cc: linux-doc@vger.kernel.org >> Signed-off-by: Lu Baolu >> --- >> 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 >> +: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. Best regards, Lu Baolu > > BR, > Peter Chen >