From 1b5aeebf3a92273b4d85aeff37a16037bc3c3abf Mon Sep 17 00:00:00 2001 From: Lu Baolu Date: Tue, 21 Mar 2017 16:01:31 +0800 Subject: x86/earlyprintk: Add support for earlyprintk via USB3 debug port Add support for earlyprintk by writing debug messages to the USB3 debug port. Users can use this type of early printk by specifying the kernel parameter of "earlyprintk=xdbc". This gives users a chance of providing debugging output. The hardware for USB3 debug port requires DMA memory blocks. This requires to delay setting up debugging hardware and registering boot console until the memblocks are filled. Signed-off-by: Lu Baolu Acked-by: Thomas Gleixner Cc: Greg Kroah-Hartman Cc: Linus Torvalds Cc: Mathias Nyman Cc: Peter Zijlstra Cc: linux-usb@vger.kernel.org Link: http://lkml.kernel.org/r/1490083293-3792-4-git-send-email-baolu.lu@linux.intel.com Signed-off-by: Ingo Molnar --- Documentation/admin-guide/kernel-parameters.txt | 1 + 1 file changed, 1 insertion(+) (limited to 'Documentation') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2ba45caabada..ea1293d60f17 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -989,6 +989,7 @@ earlyprintk=ttySn[,baudrate] earlyprintk=dbgp[debugController#] earlyprintk=pciserial,bus:device.function[,baudrate] + earlyprintk=xdbc[xhciController#] earlyprintk is useful when the kernel crashes before the normal console is initialized. It is not enabled by -- cgit v1.2.3 From 1b326277798aa820c1043617786609b9bb4bee78 Mon Sep 17 00:00:00 2001 From: Lu Baolu Date: Tue, 21 Mar 2017 16:01:33 +0800 Subject: usb/doc: Add document for USB3 debug port usage Add Documentation/usb/usb3-debug-port.rst. This document includes the guide for using USB3 debug port. Signed-off-by: Lu Baolu Acked-by: Thomas Gleixner Cc: Greg Kroah-Hartman Cc: Linus Torvalds Cc: Mathias Nyman Cc: Peter Zijlstra Cc: linux-doc@vger.kernel.org Cc: linux-usb@vger.kernel.org Link: http://lkml.kernel.org/r/1490083293-3792-6-git-send-email-baolu.lu@linux.intel.com Signed-off-by: Ingo Molnar --- Documentation/usb/usb3-debug-port.rst | 100 ++++++++++++++++++++++++++++++++++ 1 file changed, 100 insertions(+) create mode 100644 Documentation/usb/usb3-debug-port.rst (limited to 'Documentation') diff --git a/Documentation/usb/usb3-debug-port.rst b/Documentation/usb/usb3-debug-port.rst new file mode 100644 index 000000000000..feb1a36a65b7 --- /dev/null +++ b/Documentation/usb/usb3-debug-port.rst @@ -0,0 +1,100 @@ +=============== +USB3 debug port +=============== + +:Author: Lu Baolu +:Date: March 2017 + +GENERAL +======= + +This is a HOWTO for using the USB3 debug port on x86 systems. + +Before using any kernel debugging functionality based on USB3 +debug port, you need to:: + + 1) check whether any USB3 debug port is available in + your system; + 2) check which port is used for debugging purposes; + 3) have a USB 3.0 super-speed A-to-A debugging cable. + +INTRODUCTION +============ + +The xHCI debug capability (DbC) is an optional but standalone +functionality provided by the xHCI host controller. The xHCI +specification describes DbC in the section 7.6. + +When DbC is initialized and enabled, it will present a debug +device through the debug port (normally the first USB3 +super-speed port). The debug device is fully compliant with +the USB framework and provides the equivalent of a very high +performance full-duplex serial link between the debug target +(the system under debugging) and a debug host. + +EARLY PRINTK +============ + +DbC has been designed to log early printk messages. One use for +this feature is kernel debugging. For example, when your machine +crashes very early before the regular console code is initialized. +Other uses include simpler, lockless logging instead of a full- +blown printk console driver and klogd. + +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 your system, you can +append a host contoller index to this kernel parameter. This +index starts from 0. + +Current design doesn't support DbC runtime suspend/resume. As +the result, you'd better disable runtime power management for +USB subsystem by adding below kernel boot parameter:: + + "usbcore.autosuspend=-1" + +Before starting the debug target, you should connect the debug +port to a USB port (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 the debug target, DbC will be detected and +initialized. After initialization, the debug host should be able +to enumerate the debug device in debug target. The debug host +will then bind the debug device with the usb_debug driver module +and create the /dev/ttyUSB device. + +If the debug device enumeration goes smoothly, you should be able +to see below kernel messages on the 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 use any communication program, for example minicom, to +read and view the messages. Below simple bash scripts can help +you to check the sanity of the setup. + +.. code-block:: sh + + ===== start of bash scripts ============= + #!/bin/bash + + while true ; do + while [ ! -d /sys/class/tty/ttyUSB0 ] ; do + : + done + cat /dev/ttyUSB0 + done + ===== end of bash scripts =============== -- cgit v1.2.3