Commit | Line | Data |
---|---|---|
f212ec4b BK |
1 | |
2 | Using physical DMA provided by OHCI-1394 FireWire controllers for debugging | |
3 | --------------------------------------------------------------------------- | |
4 | ||
5 | Introduction | |
6 | ------------ | |
7 | ||
8 | Basically all FireWire controllers which are in use today are compliant | |
9 | to the OHCI-1394 specification which defines the controller to be a PCI | |
10 | bus master which uses DMA to offload data transfers from the CPU and has | |
11 | a "Physical Response Unit" which executes specific requests by employing | |
12 | PCI-Bus master DMA after applying filters defined by the OHCI-1394 driver. | |
13 | ||
14 | Once properly configured, remote machines can send these requests to | |
15 | ask the OHCI-1394 controller to perform read and write requests on | |
16 | physical system memory and, for read requests, send the result of | |
17 | the physical memory read back to the requester. | |
18 | ||
19 | With that, it is possible to debug issues by reading interesting memory | |
20 | locations such as buffers like the printk buffer or the process table. | |
21 | ||
22 | Retrieving a full system memory dump is also possible over the FireWire, | |
23 | using data transfer rates in the order of 10MB/s or more. | |
24 | ||
fcd46b34 SR |
25 | With most FireWire controllers, memory access is limited to the low 4 GB |
26 | of physical address space. This can be a problem on IA64 machines where | |
27 | memory is located mostly above that limit, but it is rarely a problem on | |
28 | more common hardware such as x86, x86-64 and PowerPC. However, at least | |
29 | Agere/LSI FW643e and FW643e2 controllers are known to support access to | |
30 | physical addresses above 4 GB. | |
f212ec4b BK |
31 | |
32 | Together with a early initialization of the OHCI-1394 controller for debugging, | |
33 | this facility proved most useful for examining long debugs logs in the printk | |
34 | buffer on to debug early boot problems in areas like ACPI where the system | |
35 | fails to boot and other means for debugging (serial port) are either not | |
36 | available (notebooks) or too slow for extensive debug information (like ACPI). | |
37 | ||
38 | Drivers | |
39 | ------- | |
40 | ||
a9954ce7 | 41 | The firewire-ohci driver in drivers/firewire uses filtered physical |
080de8c2 | 42 | DMA by default, which is more secure but not suitable for remote debugging. |
8bc588e0 | 43 | Pass the remote_dma=1 parameter to the driver to get unfiltered physical DMA. |
09d7328e | 44 | |
a9954ce7 | 45 | Because the firewire-ohci driver depends on the PCI enumeration to be |
080de8c2 SR |
46 | completed, an initialization routine which runs pretty early has been |
47 | implemented for x86. This routine runs long before console_init() can be | |
48 | called, i.e. before the printk buffer appears on the console. | |
f212ec4b BK |
49 | |
50 | To activate it, enable CONFIG_PROVIDE_OHCI1394_DMA_INIT (Kernel hacking menu: | |
080de8c2 SR |
51 | Remote debugging over FireWire early on boot) and pass the parameter |
52 | "ohci1394_dma=early" to the recompiled kernel on boot. | |
f212ec4b BK |
53 | |
54 | Tools | |
55 | ----- | |
56 | ||
57 | firescope - Originally developed by Benjamin Herrenschmidt, Andi Kleen ported | |
58 | it from PowerPC to x86 and x86_64 and added functionality, firescope can now | |
59 | be used to view the printk buffer of a remote machine, even with live update. | |
60 | ||
61 | Bernhard Kaindl enhanced firescope to support accessing 64-bit machines | |
62 | from 32-bit firescope and vice versa: | |
a9954ce7 | 63 | - http://v3.sk/~lkundrak/firescope/ |
f212ec4b BK |
64 | |
65 | and he implemented fast system dump (alpha version - read README.txt): | |
211a6417 | 66 | - http://halobates.de/firewire/firedump-0.1.tar.bz2 |
f212ec4b BK |
67 | |
68 | There is also a gdb proxy for firewire which allows to use gdb to access | |
69 | data which can be referenced from symbols found by gdb in vmlinux: | |
211a6417 | 70 | - http://halobates.de/firewire/fireproxy-0.33.tar.bz2 |
f212ec4b BK |
71 | |
72 | The latest version of this gdb proxy (fireproxy-0.34) can communicate (not | |
73 | yet stable) with kgdb over an memory-based communication module (kgdbom). | |
74 | ||
75 | Getting Started | |
76 | --------------- | |
77 | ||
78 | The OHCI-1394 specification regulates that the OHCI-1394 controller must | |
79 | disable all physical DMA on each bus reset. | |
80 | ||
81 | This means that if you want to debug an issue in a system state where | |
82 | interrupts are disabled and where no polling of the OHCI-1394 controller | |
83 | for bus resets takes place, you have to establish any FireWire cable | |
84 | connections and fully initialize all FireWire hardware __before__ the | |
85 | system enters such state. | |
86 | ||
87 | Step-by-step instructions for using firescope with early OHCI initialization: | |
88 | ||
89 | 1) Verify that your hardware is supported: | |
90 | ||
a9954ce7 | 91 | Load the firewire-ohci module and check your kernel logs. |
f212ec4b BK |
92 | You should see a line similar to |
93 | ||
a9954ce7 LR |
94 | firewire_ohci 0000:15:00.1: added OHCI v1.0 device as card 2, 4 IR + 4 IT |
95 | ... contexts, quirks 0x11 | |
f212ec4b BK |
96 | |
97 | when loading the driver. If you have no supported controller, many PCI, | |
98 | CardBus and even some Express cards which are fully compliant to OHCI-1394 | |
99 | specification are available. If it requires no driver for Windows operating | |
100 | systems, it most likely is. Only specialized shops have cards which are not | |
101 | compliant, they are based on TI PCILynx chips and require drivers for Win- | |
102 | dows operating systems. | |
103 | ||
fcd46b34 SR |
104 | The mentioned kernel log message contains ">4 GB phys DMA" in case of |
105 | OHCI-1394 controllers which support accesses above this limit. | |
106 | ||
f212ec4b BK |
107 | 2) Establish a working FireWire cable connection: |
108 | ||
109 | Any FireWire cable, as long at it provides electrically and mechanically | |
110 | stable connection and has matching connectors (there are small 4-pin and | |
111 | large 6-pin FireWire ports) will do. | |
112 | ||
113 | If an driver is running on both machines you should see a line like | |
114 | ||
a9954ce7 | 115 | firewire_core 0000:15:00.1: created device fw1: GUID 00061b0020105917, S400 |
f212ec4b BK |
116 | |
117 | on both machines in the kernel log when the cable is plugged in | |
118 | and connects the two machines. | |
119 | ||
120 | 3) Test physical DMA using firescope: | |
121 | ||
a9954ce7 | 122 | On the debug host, make sure that /dev/fw* is accessible, |
f212ec4b BK |
123 | then start firescope: |
124 | ||
125 | $ firescope | |
a9954ce7 | 126 | Port 0 (/dev/fw1) opened, 2 nodes detected |
f212ec4b BK |
127 | |
128 | FireScope | |
129 | --------- | |
130 | Target : <unspecified> | |
131 | Gen : 1 | |
132 | [Ctrl-T] choose target | |
133 | [Ctrl-H] this menu | |
134 | [Ctrl-Q] quit | |
135 | ||
136 | ------> Press Ctrl-T now, the output should be similar to: | |
137 | ||
138 | 2 nodes available, local node is: 0 | |
139 | 0: ffc0, uuid: 00000000 00000000 [LOCAL] | |
140 | 1: ffc1, uuid: 00279000 ba4bb801 | |
141 | ||
142 | Besides the [LOCAL] node, it must show another node without error message. | |
143 | ||
144 | 4) Prepare for debugging with early OHCI-1394 initialization: | |
145 | ||
146 | 4.1) Kernel compilation and installation on debug target | |
147 | ||
148 | Compile the kernel to be debugged with CONFIG_PROVIDE_OHCI1394_DMA_INIT | |
149 | (Kernel hacking: Provide code for enabling DMA over FireWire early on boot) | |
150 | enabled and install it on the machine to be debugged (debug target). | |
151 | ||
152 | 4.2) Transfer the System.map of the debugged kernel to the debug host | |
153 | ||
154 | Copy the System.map of the kernel be debugged to the debug host (the host | |
155 | which is connected to the debugged machine over the FireWire cable). | |
156 | ||
157 | 5) Retrieving the printk buffer contents: | |
158 | ||
159 | With the FireWire cable connected, the OHCI-1394 driver on the debugging | |
160 | host loaded, reboot the debugged machine, booting the kernel which has | |
161 | CONFIG_PROVIDE_OHCI1394_DMA_INIT enabled, with the option ohci1394_dma=early. | |
162 | ||
163 | Then, on the debugging host, run firescope, for example by using -A: | |
164 | ||
165 | firescope -A System.map-of-debug-target-kernel | |
166 | ||
167 | Note: -A automatically attaches to the first non-local node. It only works | |
168 | reliably if only connected two machines are connected using FireWire. | |
169 | ||
170 | After having attached to the debug target, press Ctrl-D to view the | |
171 | complete printk buffer or Ctrl-U to enter auto update mode and get an | |
172 | updated live view of recent kernel messages logged on the debug target. | |
173 | ||
174 | Call "firescope -h" to get more information on firescope's options. | |
175 | ||
176 | Notes | |
177 | ----- | |
211a6417 | 178 | Documentation and specifications: http://halobates.de/firewire/ |
f212ec4b BK |
179 | |
180 | FireWire is a trademark of Apple Inc. - for more information please refer to: | |
181 | http://en.wikipedia.org/wiki/FireWire |