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Yinghai Lua1aade42009-03-04 16:11:35 -08001
2Mini-HOWTO for using the earlyprintk=dbgp boot option with a
3USB2 Debug port key and a debug cable, on x86 systems.
4
5You need two computers, the 'USB debug key' special gadget and
6and two USB cables, connected like this:
7
8 [host/target] <-------> [USB debug key] <-------> [client/console]
9
Jason Wessel9780bc42009-08-20 15:39:57 -0500101. There are a number of specific hardware requirements:
Yinghai Lua1aade42009-03-04 16:11:35 -080011
12 a.) Host/target system needs to have USB debug port capability.
13
14 You can check this capability by looking at a 'Debug port' bit in
15 the lspci -vvv output:
16
17 # lspci -vvv
18 ...
19 00:1d.7 USB Controller: Intel Corporation 82801H (ICH8 Family) USB2 EHCI Controller #1 (rev 03) (prog-if 20 [EHCI])
20 Subsystem: Lenovo ThinkPad T61
21 Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx-
22 Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
23 Latency: 0
24 Interrupt: pin D routed to IRQ 19
25 Region 0: Memory at fe227000 (32-bit, non-prefetchable) [size=1K]
26 Capabilities: [50] Power Management version 2
27 Flags: PMEClk- DSI- D1- D2- AuxCurrent=375mA PME(D0+,D1-,D2-,D3hot+,D3cold+)
28 Status: D0 PME-Enable- DSel=0 DScale=0 PME+
29 Capabilities: [58] Debug port: BAR=1 offset=00a0
30 ^^^^^^^^^^^ <==================== [ HERE ]
31 Kernel driver in use: ehci_hcd
32 Kernel modules: ehci-hcd
33 ...
34
35( If your system does not list a debug port capability then you probably
Carlos Garciac98be0c2014-04-04 22:31:00 -040036 won't be able to use the USB debug key. )
Yinghai Lua1aade42009-03-04 16:11:35 -080037
38 b.) You also need a Netchip USB debug cable/key:
39
40 http://www.plxtech.com/products/NET2000/NET20DC/default.asp
41
42 This is a small blue plastic connector with two USB connections,
43 it draws power from its USB connections.
44
Jason Wessel9780bc42009-08-20 15:39:57 -050045 c.) You need a second client/console system with a high speed USB 2.0
46 port.
47
48 d.) The Netchip device must be plugged directly into the physical
49 debug port on the "host/target" system. You cannot use a USB hub in
50 between the physical debug port and the "host/target" system.
51
52 The EHCI debug controller is bound to a specific physical USB
53 port and the Netchip device will only work as an early printk
54 device in this port. The EHCI host controllers are electrically
55 wired such that the EHCI debug controller is hooked up to the
56 first physical and there is no way to change this via software.
57 You can find the physical port through experimentation by trying
58 each physical port on the system and rebooting. Or you can try
59 and use lsusb or look at the kernel info messages emitted by the
60 usb stack when you plug a usb device into various ports on the
61 "host/target" system.
62
63 Some hardware vendors do not expose the usb debug port with a
64 physical connector and if you find such a device send a complaint
65 to the hardware vendor, because there is no reason not to wire
66 this port into one of the physically accessible ports.
67
68 e.) It is also important to note, that many versions of the Netchip
69 device require the "client/console" system to be plugged into the
70 right and side of the device (with the product logo facing up and
71 readable left to right). The reason being is that the 5 volt
72 power supply is taken from only one side of the device and it
73 must be the side that does not get rebooted.
Yinghai Lua1aade42009-03-04 16:11:35 -080074
752. Software requirements:
76
77 a.) On the host/target system:
78
79 You need to enable the following kernel config option:
80
81 CONFIG_EARLY_PRINTK_DBGP=y
82
83 And you need to add the boot command line: "earlyprintk=dbgp".
84 (If you are using Grub, append it to the 'kernel' line in
85 /etc/grub.conf)
86
Jason Wessel9780bc42009-08-20 15:39:57 -050087 On systems with more than one EHCI debug controller you must
88 specify the correct EHCI debug controller number. The ordering
89 comes from the PCI bus enumeration of the EHCI controllers. The
90 default with no number argument is "0" the first EHCI debug
91 controller. To use the second EHCI debug controller, you would
92 use the command line: "earlyprintk=dbgp1"
93
Yinghai Lua1aade42009-03-04 16:11:35 -080094 NOTE: normally earlyprintk console gets turned off once the
95 regular console is alive - use "earlyprintk=dbgp,keep" to keep
96 this channel open beyond early bootup. This can be useful for
97 debugging crashes under Xorg, etc.
98
99 b.) On the client/console system:
100
101 You should enable the following kernel config option:
102
103 CONFIG_USB_SERIAL_DEBUG=y
104
105 On the next bootup with the modified kernel you should
106 get a /dev/ttyUSBx device(s).
107
108 Now this channel of kernel messages is ready to be used: start
109 your favorite terminal emulator (minicom, etc.) and set
110 it up to use /dev/ttyUSB0 - or use a raw 'cat /dev/ttyUSBx' to
111 see the raw output.
112
113 c.) On Nvidia Southbridge based systems: the kernel will try to probe
114 and find out which port has debug device connected.
115
1163. Testing that it works fine:
117
118 You can test the output by using earlyprintk=dbgp,keep and provoking
119 kernel messages on the host/target system. You can provoke a harmless
120 kernel message by for example doing:
121
122 echo h > /proc/sysrq-trigger
123
124 On the host/target system you should see this help line in "dmesg" output:
125
126 SysRq : HELP : loglevel(0-9) reBoot Crashdump terminate-all-tasks(E) memory-full-oom-kill(F) kill-all-tasks(I) saK show-backtrace-all-active-cpus(L) show-memory-usage(M) nice-all-RT-tasks(N) powerOff show-registers(P) show-all-timers(Q) unRaw Sync show-task-states(T) Unmount show-blocked-tasks(W) dump-ftrace-buffer(Z)
127
128 On the client/console system do:
129
130 cat /dev/ttyUSB0
131
132 And you should see the help line above displayed shortly after you've
133 provoked it on the host system.
134
135If it does not work then please ask about it on the linux-kernel@vger.kernel.org
136mailing list or contact the x86 maintainers.