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1
2 The Linux IPMI Driver
3 ---------------------
4 Corey Minyard
5 <minyard@mvista.com>
6 <minyard@acm.org>
7
8The Intelligent Platform Management Interface, or IPMI, is a
9standard for controlling intelligent devices that monitor a system.
10It provides for dynamic discovery of sensors in the system and the
11ability to monitor the sensors and be informed when the sensor's
12values change or go outside certain boundaries. It also has a
dc474c89 13standardized database for field-replaceable units (FRUs) and a watchdog
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14timer.
15
16To use this, you need an interface to an IPMI controller in your
17system (called a Baseboard Management Controller, or BMC) and
18management software that can use the IPMI system.
19
20This document describes how to use the IPMI driver for Linux. If you
21are not familiar with IPMI itself, see the web site at
22http://www.intel.com/design/servers/ipmi/index.htm. IPMI is a big
23subject and I can't cover it all here!
24
25Configuration
26-------------
27
845e78a1 28The Linux IPMI driver is modular, which means you have to pick several
1da177e4 29things to have it work right depending on your hardware. Most of
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30these are available in the 'Character Devices' menu then the IPMI
31menu.
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32
33No matter what, you must pick 'IPMI top-level message handler' to use
34IPMI. What you do beyond that depends on your needs and hardware.
35
36The message handler does not provide any user-level interfaces.
37Kernel code (like the watchdog) can still use it. If you need access
38from userland, you need to select 'Device interface for IPMI' if you
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39want access through a device driver.
40
41The driver interface depends on your hardware. If your system
42properly provides the SMBIOS info for IPMI, the driver will detect it
43and just work. If you have a board with a standard interface (These
44will generally be either "KCS", "SMIC", or "BT", consult your hardware
45manual), choose the 'IPMI SI handler' option. A driver also exists
46for direct I2C access to the IPMI management controller. Some boards
47support this, but it is unknown if it will work on every board. For
48this, choose 'IPMI SMBus handler', but be ready to try to do some
49figuring to see if it will work on your system if the SMBIOS/APCI
50information is wrong or not present. It is fairly safe to have both
51these enabled and let the drivers auto-detect what is present.
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52
53You should generally enable ACPI on your system, as systems with IPMI
845e78a1 54can have ACPI tables describing them.
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55
56If you have a standard interface and the board manufacturer has done
57their job correctly, the IPMI controller should be automatically
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58detected (via ACPI or SMBIOS tables) and should just work. Sadly,
59many boards do not have this information. The driver attempts
60standard defaults, but they may not work. If you fall into this
61situation, you need to read the section below named 'The SI Driver' or
62"The SMBus Driver" on how to hand-configure your system.
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63
64IPMI defines a standard watchdog timer. You can enable this with the
65'IPMI Watchdog Timer' config option. If you compile the driver into
66the kernel, then via a kernel command-line option you can have the
dc474c89 67watchdog timer start as soon as it initializes. It also have a lot
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68of other options, see the 'Watchdog' section below for more details.
69Note that you can also have the watchdog continue to run if it is
70closed (by default it is disabled on close). Go into the 'Watchdog
71Cards' menu, enable 'Watchdog Timer Support', and enable the option
72'Disable watchdog shutdown on close'.
73
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74IPMI systems can often be powered off using IPMI commands. Select
75'IPMI Poweroff' to do this. The driver will auto-detect if the system
76can be powered off by IPMI. It is safe to enable this even if your
77system doesn't support this option. This works on ATCA systems, the
78Radisys CPI1 card, and any IPMI system that supports standard chassis
79management commands.
80
81If you want the driver to put an event into the event log on a panic,
82enable the 'Generate a panic event to all BMCs on a panic' option. If
83you want the whole panic string put into the event log using OEM
84events, enable the 'Generate OEM events containing the panic string'
85option.
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86
87Basic Design
88------------
89
90The Linux IPMI driver is designed to be very modular and flexible, you
91only need to take the pieces you need and you can use it in many
92different ways. Because of that, it's broken into many chunks of
845e78a1 93code. These chunks (by module name) are:
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94
95ipmi_msghandler - This is the central piece of software for the IPMI
96system. It handles all messages, message timing, and responses. The
97IPMI users tie into this, and the IPMI physical interfaces (called
98System Management Interfaces, or SMIs) also tie in here. This
99provides the kernelland interface for IPMI, but does not provide an
100interface for use by application processes.
101
102ipmi_devintf - This provides a userland IOCTL interface for the IPMI
103driver, each open file for this device ties in to the message handler
104as an IPMI user.
105
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106ipmi_si - A driver for various system interfaces. This supports KCS,
107SMIC, and BT interfaces. Unless you have an SMBus interface or your
108own custom interface, you probably need to use this.
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109
110ipmi_smb - A driver for accessing BMCs on the SMBus. It uses the
111I2C kernel driver's SMBus interfaces to send and receive IPMI messages
112over the SMBus.
113
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114ipmi_watchdog - IPMI requires systems to have a very capable watchdog
115timer. This driver implements the standard Linux watchdog timer
116interface on top of the IPMI message handler.
117
118ipmi_poweroff - Some systems support the ability to be turned off via
119IPMI commands.
120
121These are all individually selectable via configuration options.
1da177e4 122
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123Note that the KCS-only interface has been removed. The af_ipmi driver
124is no longer supported and has been removed because it was impossible
125to do 32 bit emulation on 64-bit kernels with it.
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126
127Much documentation for the interface is in the include files. The
128IPMI include files are:
129
130net/af_ipmi.h - Contains the socket interface.
131
132linux/ipmi.h - Contains the user interface and IOCTL interface for IPMI.
133
134linux/ipmi_smi.h - Contains the interface for system management interfaces
135(things that interface to IPMI controllers) to use.
136
137linux/ipmi_msgdefs.h - General definitions for base IPMI messaging.
138
139
140Addressing
141----------
142
143The IPMI addressing works much like IP addresses, you have an overlay
144to handle the different address types. The overlay is:
145
146 struct ipmi_addr
147 {
148 int addr_type;
149 short channel;
150 char data[IPMI_MAX_ADDR_SIZE];
151 };
152
153The addr_type determines what the address really is. The driver
154currently understands two different types of addresses.
155
156"System Interface" addresses are defined as:
157
158 struct ipmi_system_interface_addr
159 {
160 int addr_type;
161 short channel;
162 };
163
164and the type is IPMI_SYSTEM_INTERFACE_ADDR_TYPE. This is used for talking
165straight to the BMC on the current card. The channel must be
166IPMI_BMC_CHANNEL.
167
168Messages that are destined to go out on the IPMB bus use the
169IPMI_IPMB_ADDR_TYPE address type. The format is
170
171 struct ipmi_ipmb_addr
172 {
173 int addr_type;
174 short channel;
175 unsigned char slave_addr;
176 unsigned char lun;
177 };
178
179The "channel" here is generally zero, but some devices support more
180than one channel, it corresponds to the channel as defined in the IPMI
181spec.
182
183
184Messages
185--------
186
187Messages are defined as:
188
189struct ipmi_msg
190{
191 unsigned char netfn;
192 unsigned char lun;
193 unsigned char cmd;
194 unsigned char *data;
195 int data_len;
196};
197
198The driver takes care of adding/stripping the header information. The
199data portion is just the data to be send (do NOT put addressing info
200here) or the response. Note that the completion code of a response is
201the first item in "data", it is not stripped out because that is how
202all the messages are defined in the spec (and thus makes counting the
203offsets a little easier :-).
204
205When using the IOCTL interface from userland, you must provide a block
206of data for "data", fill it, and set data_len to the length of the
207block of data, even when receiving messages. Otherwise the driver
208will have no place to put the message.
209
210Messages coming up from the message handler in kernelland will come in
211as:
212
213 struct ipmi_recv_msg
214 {
215 struct list_head link;
216
217 /* The type of message as defined in the "Receive Types"
218 defines above. */
219 int recv_type;
220
221 ipmi_user_t *user;
222 struct ipmi_addr addr;
223 long msgid;
224 struct ipmi_msg msg;
225
226 /* Call this when done with the message. It will presumably free
227 the message and do any other necessary cleanup. */
228 void (*done)(struct ipmi_recv_msg *msg);
229
230 /* Place-holder for the data, don't make any assumptions about
231 the size or existence of this, since it may change. */
232 unsigned char msg_data[IPMI_MAX_MSG_LENGTH];
233 };
234
235You should look at the receive type and handle the message
236appropriately.
237
238
239The Upper Layer Interface (Message Handler)
240-------------------------------------------
241
242The upper layer of the interface provides the users with a consistent
243view of the IPMI interfaces. It allows multiple SMI interfaces to be
244addressed (because some boards actually have multiple BMCs on them)
245and the user should not have to care what type of SMI is below them.
246
247
248Creating the User
249
250To user the message handler, you must first create a user using
251ipmi_create_user. The interface number specifies which SMI you want
252to connect to, and you must supply callback functions to be called
253when data comes in. The callback function can run at interrupt level,
254so be careful using the callbacks. This also allows to you pass in a
255piece of data, the handler_data, that will be passed back to you on
256all calls.
257
258Once you are done, call ipmi_destroy_user() to get rid of the user.
259
260From userland, opening the device automatically creates a user, and
261closing the device automatically destroys the user.
262
263
264Messaging
265
266To send a message from kernel-land, the ipmi_request() call does
267pretty much all message handling. Most of the parameter are
268self-explanatory. However, it takes a "msgid" parameter. This is NOT
269the sequence number of messages. It is simply a long value that is
270passed back when the response for the message is returned. You may
271use it for anything you like.
272
273Responses come back in the function pointed to by the ipmi_recv_hndl
274field of the "handler" that you passed in to ipmi_create_user().
275Remember again, these may be running at interrupt level. Remember to
276look at the receive type, too.
277
278From userland, you fill out an ipmi_req_t structure and use the
279IPMICTL_SEND_COMMAND ioctl. For incoming stuff, you can use select()
280or poll() to wait for messages to come in. However, you cannot use
281read() to get them, you must call the IPMICTL_RECEIVE_MSG with the
282ipmi_recv_t structure to actually get the message. Remember that you
283must supply a pointer to a block of data in the msg.data field, and
284you must fill in the msg.data_len field with the size of the data.
285This gives the receiver a place to actually put the message.
286
287If the message cannot fit into the data you provide, you will get an
288EMSGSIZE error and the driver will leave the data in the receive
289queue. If you want to get it and have it truncate the message, us
290the IPMICTL_RECEIVE_MSG_TRUNC ioctl.
291
292When you send a command (which is defined by the lowest-order bit of
293the netfn per the IPMI spec) on the IPMB bus, the driver will
294automatically assign the sequence number to the command and save the
295command. If the response is not receive in the IPMI-specified 5
296seconds, it will generate a response automatically saying the command
297timed out. If an unsolicited response comes in (if it was after 5
298seconds, for instance), that response will be ignored.
299
300In kernelland, after you receive a message and are done with it, you
301MUST call ipmi_free_recv_msg() on it, or you will leak messages. Note
302that you should NEVER mess with the "done" field of a message, that is
303required to properly clean up the message.
304
305Note that when sending, there is an ipmi_request_supply_msgs() call
306that lets you supply the smi and receive message. This is useful for
307pieces of code that need to work even if the system is out of buffers
308(the watchdog timer uses this, for instance). You supply your own
309buffer and own free routines. This is not recommended for normal use,
310though, since it is tricky to manage your own buffers.
311
312
313Events and Incoming Commands
314
315The driver takes care of polling for IPMI events and receiving
316commands (commands are messages that are not responses, they are
317commands that other things on the IPMB bus have sent you). To receive
318these, you must register for them, they will not automatically be sent
319to you.
320
321To receive events, you must call ipmi_set_gets_events() and set the
322"val" to non-zero. Any events that have been received by the driver
323since startup will immediately be delivered to the first user that
324registers for events. After that, if multiple users are registered
325for events, they will all receive all events that come in.
326
327For receiving commands, you have to individually register commands you
328want to receive. Call ipmi_register_for_cmd() and supply the netfn
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329and command name for each command you want to receive. You also
330specify a bitmask of the channels you want to receive the command from
331(or use IPMI_CHAN_ALL for all channels if you don't care). Only one
332user may be registered for each netfn/cmd/channel, but different users
333may register for different commands, or the same command if the
334channel bitmasks do not overlap.
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335
336From userland, equivalent IOCTLs are provided to do these functions.
337
338
339The Lower Layer (SMI) Interface
340-------------------------------
341
342As mentioned before, multiple SMI interfaces may be registered to the
343message handler, each of these is assigned an interface number when
344they register with the message handler. They are generally assigned
345in the order they register, although if an SMI unregisters and then
346another one registers, all bets are off.
347
348The ipmi_smi.h defines the interface for management interfaces, see
349that for more details.
350
351
352The SI Driver
353-------------
354
355The SI driver allows up to 4 KCS or SMIC interfaces to be configured
356in the system. By default, scan the ACPI tables for interfaces, and
357if it doesn't find any the driver will attempt to register one KCS
358interface at the spec-specified I/O port 0xca2 without interrupts.
359You can change this at module load time (for a module) with:
360
361 modprobe ipmi_si.o type=<type1>,<type2>....
362 ports=<port1>,<port2>... addrs=<addr1>,<addr2>...
363 irqs=<irq1>,<irq2>... trydefaults=[0|1]
364 regspacings=<sp1>,<sp2>,... regsizes=<size1>,<size2>,...
365 regshifts=<shift1>,<shift2>,...
366 slave_addrs=<addr1>,<addr2>,...
a51f4a81 367 force_kipmid=<enable1>,<enable2>,...
b361e27b 368 unload_when_empty=[0|1]
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369
370Each of these except si_trydefaults is a list, the first item for the
371first interface, second item for the second interface, etc.
372
373The si_type may be either "kcs", "smic", or "bt". If you leave it blank, it
374defaults to "kcs".
375
376If you specify si_addrs as non-zero for an interface, the driver will
377use the memory address given as the address of the device. This
378overrides si_ports.
379
380If you specify si_ports as non-zero for an interface, the driver will
381use the I/O port given as the device address.
382
383If you specify si_irqs as non-zero for an interface, the driver will
384attempt to use the given interrupt for the device.
385
386si_trydefaults sets whether the standard IPMI interface at 0xca2 and
387any interfaces specified by ACPE are tried. By default, the driver
388tries it, set this value to zero to turn this off.
389
390The next three parameters have to do with register layout. The
391registers used by the interfaces may not appear at successive
392locations and they may not be in 8-bit registers. These parameters
393allow the layout of the data in the registers to be more precisely
394specified.
395
396The regspacings parameter give the number of bytes between successive
397register start addresses. For instance, if the regspacing is set to 4
398and the start address is 0xca2, then the address for the second
399register would be 0xca6. This defaults to 1.
400
401The regsizes parameter gives the size of a register, in bytes. The
402data used by IPMI is 8-bits wide, but it may be inside a larger
403register. This parameter allows the read and write type to specified.
404It may be 1, 2, 4, or 8. The default is 1.
405
406Since the register size may be larger than 32 bits, the IPMI data may not
407be in the lower 8 bits. The regshifts parameter give the amount to shift
408the data to get to the actual IPMI data.
409
410The slave_addrs specifies the IPMI address of the local BMC. This is
411usually 0x20 and the driver defaults to that, but in case it's not, it
412can be specified when the driver starts up.
413
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414The force_ipmid parameter forcefully enables (if set to 1) or disables
415(if set to 0) the kernel IPMI daemon. Normally this is auto-detected
416by the driver, but systems with broken interrupts might need an enable,
417or users that don't want the daemon (don't need the performance, don't
418want the CPU hit) can disable it.
419
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420If unload_when_empty is set to 1, the driver will be unloaded if it
421doesn't find any interfaces or all the interfaces fail to work. The
422default is one. Setting to 0 is useful with the hotmod, but is
423obviously only useful for modules.
424
a51f4a81 425When compiled into the kernel, the parameters can be specified on the
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426kernel command line as:
427
428 ipmi_si.type=<type1>,<type2>...
429 ipmi_si.ports=<port1>,<port2>... ipmi_si.addrs=<addr1>,<addr2>...
430 ipmi_si.irqs=<irq1>,<irq2>... ipmi_si.trydefaults=[0|1]
431 ipmi_si.regspacings=<sp1>,<sp2>,...
432 ipmi_si.regsizes=<size1>,<size2>,...
433 ipmi_si.regshifts=<shift1>,<shift2>,...
434 ipmi_si.slave_addrs=<addr1>,<addr2>,...
a51f4a81 435 ipmi_si.force_kipmid=<enable1>,<enable2>,...
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436
437It works the same as the module parameters of the same names.
438
439By default, the driver will attempt to detect any device specified by
440ACPI, and if none of those then a KCS device at the spec-specified
4410xca2. If you want to turn this off, set the "trydefaults" option to
442false.
443
444If you have high-res timers compiled into the kernel, the driver will
445use them to provide much better performance. Note that if you do not
446have high-res timers enabled in the kernel and you don't have
447interrupts enabled, the driver will run VERY slowly. Don't blame me,
448these interfaces suck.
449
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450The driver supports a hot add and remove of interfaces. This way,
451interfaces can be added or removed after the kernel is up and running.
452This is done using /sys/modules/ipmi_si/hotmod, which is a write-only
453parameter. You write a string to this interface. The string has the
454format:
455 <op1>[:op2[:op3...]]
456The "op"s are:
457 add|remove,kcs|bt|smic,mem|i/o,<address>[,<opt1>[,<opt2>[,...]]]
458You can specify more than one interface on the line. The "opt"s are:
459 rsp=<regspacing>
460 rsi=<regsize>
461 rsh=<regshift>
462 irq=<irq>
463 ipmb=<ipmb slave addr>
464and these have the same meanings as discussed above. Note that you
465can also use this on the kernel command line for a more compact format
466for specifying an interface. Note that when removing an interface,
467only the first three parameters (si type, address type, and address)
468are used for the comparison. Any options are ignored for removing.
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469
470The SMBus Driver
471----------------
472
473The SMBus driver allows up to 4 SMBus devices to be configured in the
474system. By default, the driver will register any SMBus interfaces it finds
475in the I2C address range of 0x20 to 0x4f on any adapter. You can change this
476at module load time (for a module) with:
477
478 modprobe ipmi_smb.o
479 addr=<adapter1>,<i2caddr1>[,<adapter2>,<i2caddr2>[,...]]
480 dbg=<flags1>,<flags2>...
845e78a1 481 [defaultprobe=1] [dbg_probe=1]
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482
483The addresses are specified in pairs, the first is the adapter ID and the
484second is the I2C address on that adapter.
485
486The debug flags are bit flags for each BMC found, they are:
487IPMI messages: 1, driver state: 2, timing: 4, I2C probe: 8
488
489Setting smb_defaultprobe to zero disabled the default probing of SMBus
490interfaces at address range 0x20 to 0x4f. This means that only the
491BMCs specified on the smb_addr line will be detected.
492
493Setting smb_dbg_probe to 1 will enable debugging of the probing and
494detection process for BMCs on the SMBusses.
495
6c28f2c0 496Discovering the IPMI compliant BMC on the SMBus can cause devices
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497on the I2C bus to fail. The SMBus driver writes a "Get Device ID" IPMI
498message as a block write to the I2C bus and waits for a response.
499This action can be detrimental to some I2C devices. It is highly recommended
500that the known I2c address be given to the SMBus driver in the smb_addr
3f6dee9b 501parameter. The default address range will not be used when a smb_addr
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502parameter is provided.
503
504When compiled into the kernel, the addresses can be specified on the
505kernel command line as:
506
507 ipmb_smb.addr=<adapter1>,<i2caddr1>[,<adapter2>,<i2caddr2>[,...]]
508 ipmi_smb.dbg=<flags1>,<flags2>...
509 ipmi_smb.defaultprobe=0 ipmi_smb.dbg_probe=1
510
511These are the same options as on the module command line.
512
513Note that you might need some I2C changes if CONFIG_IPMI_PANIC_EVENT
514is enabled along with this, so the I2C driver knows to run to
515completion during sending a panic event.
516
517
518Other Pieces
519------------
520
521Watchdog
522--------
523
524A watchdog timer is provided that implements the Linux-standard
525watchdog timer interface. It has three module parameters that can be
526used to control it:
527
528 modprobe ipmi_watchdog timeout=<t> pretimeout=<t> action=<action type>
529 preaction=<preaction type> preop=<preop type> start_now=x
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530 nowayout=x ifnum_to_use=n
531
532ifnum_to_use specifies which interface the watchdog timer should use.
533The default is -1, which means to pick the first one registered.
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534
535The timeout is the number of seconds to the action, and the pretimeout
536is the amount of seconds before the reset that the pre-timeout panic will
537occur (if pretimeout is zero, then pretimeout will not be enabled). Note
538that the pretimeout is the time before the final timeout. So if the
539timeout is 50 seconds and the pretimeout is 10 seconds, then the pretimeout
540will occur in 40 second (10 seconds before the timeout).
541
542The action may be "reset", "power_cycle", or "power_off", and
543specifies what to do when the timer times out, and defaults to
544"reset".
545
546The preaction may be "pre_smi" for an indication through the SMI
547interface, "pre_int" for an indication through the SMI with an
548interrupts, and "pre_nmi" for a NMI on a preaction. This is how
549the driver is informed of the pretimeout.
550
551The preop may be set to "preop_none" for no operation on a pretimeout,
552"preop_panic" to set the preoperation to panic, or "preop_give_data"
553to provide data to read from the watchdog device when the pretimeout
554occurs. A "pre_nmi" setting CANNOT be used with "preop_give_data"
555because you can't do data operations from an NMI.
556
557When preop is set to "preop_give_data", one byte comes ready to read
558on the device when the pretimeout occurs. Select and fasync work on
559the device, as well.
560
561If start_now is set to 1, the watchdog timer will start running as
562soon as the driver is loaded.
563
564If nowayout is set to 1, the watchdog timer will not stop when the
565watchdog device is closed. The default value of nowayout is true
566if the CONFIG_WATCHDOG_NOWAYOUT option is enabled, or false if not.
567
568When compiled into the kernel, the kernel command line is available
569for configuring the watchdog:
570
571 ipmi_watchdog.timeout=<t> ipmi_watchdog.pretimeout=<t>
572 ipmi_watchdog.action=<action type>
573 ipmi_watchdog.preaction=<preaction type>
574 ipmi_watchdog.preop=<preop type>
575 ipmi_watchdog.start_now=x
576 ipmi_watchdog.nowayout=x
577
578The options are the same as the module parameter options.
579
580The watchdog will panic and start a 120 second reset timeout if it
581gets a pre-action. During a panic or a reboot, the watchdog will
582start a 120 timer if it is running to make sure the reboot occurs.
583
584Note that if you use the NMI preaction for the watchdog, you MUST
585NOT use nmi watchdog mode 1. If you use the NMI watchdog, you
586must use mode 2.
587
588Once you open the watchdog timer, you must write a 'V' character to the
589device to close it, or the timer will not stop. This is a new semantic
590for the driver, but makes it consistent with the rest of the watchdog
591drivers in Linux.
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592
593
594Panic Timeouts
595--------------
596
597The OpenIPMI driver supports the ability to put semi-custom and custom
598events in the system event log if a panic occurs. if you enable the
599'Generate a panic event to all BMCs on a panic' option, you will get
600one event on a panic in a standard IPMI event format. If you enable
601the 'Generate OEM events containing the panic string' option, you will
602also get a bunch of OEM events holding the panic string.
603
604
605The field settings of the events are:
606* Generator ID: 0x21 (kernel)
607* EvM Rev: 0x03 (this event is formatting in IPMI 1.0 format)
608* Sensor Type: 0x20 (OS critical stop sensor)
609* Sensor #: The first byte of the panic string (0 if no panic string)
610* Event Dir | Event Type: 0x6f (Assertion, sensor-specific event info)
611* Event Data 1: 0xa1 (Runtime stop in OEM bytes 2 and 3)
612* Event data 2: second byte of panic string
613* Event data 3: third byte of panic string
614See the IPMI spec for the details of the event layout. This event is
615always sent to the local management controller. It will handle routing
616the message to the right place
617
618Other OEM events have the following format:
619Record ID (bytes 0-1): Set by the SEL.
620Record type (byte 2): 0xf0 (OEM non-timestamped)
621byte 3: The slave address of the card saving the panic
622byte 4: A sequence number (starting at zero)
623The rest of the bytes (11 bytes) are the panic string. If the panic string
624is longer than 11 bytes, multiple messages will be sent with increasing
625sequence numbers.
626
627Because you cannot send OEM events using the standard interface, this
628function will attempt to find an SEL and add the events there. It
629will first query the capabilities of the local management controller.
630If it has an SEL, then they will be stored in the SEL of the local
631management controller. If not, and the local management controller is
632an event generator, the event receiver from the local management
633controller will be queried and the events sent to the SEL on that
634device. Otherwise, the events go nowhere since there is nowhere to
635send them.
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636
637
638Poweroff
639--------
640
641If the poweroff capability is selected, the IPMI driver will install
642a shutdown function into the standard poweroff function pointer. This
643is in the ipmi_poweroff module. When the system requests a powerdown,
644it will send the proper IPMI commands to do this. This is supported on
645several platforms.
646
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647There is a module parameter named "poweroff_powercycle" that may
648either be zero (do a power down) or non-zero (do a power cycle, power
649the system off, then power it on in a few seconds). Setting
650ipmi_poweroff.poweroff_control=x will do the same thing on the kernel
651command line. The parameter is also available via the proc filesystem
652in /proc/sys/dev/ipmi/poweroff_powercycle. Note that if the system
653does not support power cycling, it will always do the power off.
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655The "ifnum_to_use" parameter specifies which interface the poweroff
656code should use. The default is -1, which means to pick the first one
657registered.
658
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659Note that if you have ACPI enabled, the system will prefer using ACPI to
660power off.