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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	=====================
2	The Linux IPMI Driver
3	=====================
4	
5	:Author: Corey Minyard <minyard@mvista.com> / <minyard@acm.org>
6	
7	The Intelligent Platform Management Interface, or IPMI, is a
8	standard for controlling intelligent devices that monitor a system.
9	It provides for dynamic discovery of sensors in the system and the
10	ability to monitor the sensors and be informed when the sensor's
11	values change or go outside certain boundaries.  It also has a
12	standardized database for field-replaceable units (FRUs) and a watchdog
13	timer.
14	
15	To use this, you need an interface to an IPMI controller in your
16	system (called a Baseboard Management Controller, or BMC) and
17	management software that can use the IPMI system.
18	
19	This document describes how to use the IPMI driver for Linux.  If you
20	are not familiar with IPMI itself, see the web site at
21	http://www.intel.com/design/servers/ipmi/index.htm.  IPMI is a big
22	subject and I can't cover it all here!
23	
24	Configuration
25	-------------
26	
27	The Linux IPMI driver is modular, which means you have to pick several
28	things to have it work right depending on your hardware.  Most of
29	these are available in the 'Character Devices' menu then the IPMI
30	menu.
31	
32	No matter what, you must pick 'IPMI top-level message handler' to use
33	IPMI.  What you do beyond that depends on your needs and hardware.
34	
35	The message handler does not provide any user-level interfaces.
36	Kernel code (like the watchdog) can still use it.  If you need access
37	from userland, you need to select 'Device interface for IPMI' if you
38	want access through a device driver.
39	
40	The driver interface depends on your hardware.  If your system
41	properly provides the SMBIOS info for IPMI, the driver will detect it
42	and just work.  If you have a board with a standard interface (These
43	will generally be either "KCS", "SMIC", or "BT", consult your hardware
44	manual), choose the 'IPMI SI handler' option.  A driver also exists
45	for direct I2C access to the IPMI management controller.  Some boards
46	support this, but it is unknown if it will work on every board.  For
47	this, choose 'IPMI SMBus handler', but be ready to try to do some
48	figuring to see if it will work on your system if the SMBIOS/APCI
49	information is wrong or not present.  It is fairly safe to have both
50	these enabled and let the drivers auto-detect what is present.
51	
52	You should generally enable ACPI on your system, as systems with IPMI
53	can have ACPI tables describing them.
54	
55	If you have a standard interface and the board manufacturer has done
56	their job correctly, the IPMI controller should be automatically
57	detected (via ACPI or SMBIOS tables) and should just work.  Sadly,
58	many boards do not have this information.  The driver attempts
59	standard defaults, but they may not work.  If you fall into this
60	situation, you need to read the section below named 'The SI Driver' or
61	"The SMBus Driver" on how to hand-configure your system.
62	
63	IPMI defines a standard watchdog timer.  You can enable this with the
64	'IPMI Watchdog Timer' config option.  If you compile the driver into
65	the kernel, then via a kernel command-line option you can have the
66	watchdog timer start as soon as it initializes.  It also have a lot
67	of other options, see the 'Watchdog' section below for more details.
68	Note that you can also have the watchdog continue to run if it is
69	closed (by default it is disabled on close).  Go into the 'Watchdog
70	Cards' menu, enable 'Watchdog Timer Support', and enable the option
71	'Disable watchdog shutdown on close'.
72	
73	IPMI systems can often be powered off using IPMI commands.  Select
74	'IPMI Poweroff' to do this.  The driver will auto-detect if the system
75	can be powered off by IPMI.  It is safe to enable this even if your
76	system doesn't support this option.  This works on ATCA systems, the
77	Radisys CPI1 card, and any IPMI system that supports standard chassis
78	management commands.
79	
80	If you want the driver to put an event into the event log on a panic,
81	enable the 'Generate a panic event to all BMCs on a panic' option.  If
82	you want the whole panic string put into the event log using OEM
83	events, enable the 'Generate OEM events containing the panic string'
84	option.
85	
86	Basic Design
87	------------
88	
89	The Linux IPMI driver is designed to be very modular and flexible, you
90	only need to take the pieces you need and you can use it in many
91	different ways.  Because of that, it's broken into many chunks of
92	code.  These chunks (by module name) are:
93	
94	ipmi_msghandler - This is the central piece of software for the IPMI
95	system.  It handles all messages, message timing, and responses.  The
96	IPMI users tie into this, and the IPMI physical interfaces (called
97	System Management Interfaces, or SMIs) also tie in here.  This
98	provides the kernelland interface for IPMI, but does not provide an
99	interface for use by application processes.
100	
101	ipmi_devintf - This provides a userland IOCTL interface for the IPMI
102	driver, each open file for this device ties in to the message handler
103	as an IPMI user.
104	
105	ipmi_si - A driver for various system interfaces.  This supports KCS,
106	SMIC, and BT interfaces.  Unless you have an SMBus interface or your
107	own custom interface, you probably need to use this.
108	
109	ipmi_ssif - A driver for accessing BMCs on the SMBus. It uses the
110	I2C kernel driver's SMBus interfaces to send and receive IPMI messages
111	over the SMBus.
112	
113	ipmi_powernv - A driver for access BMCs on POWERNV systems.
114	
115	ipmi_watchdog - IPMI requires systems to have a very capable watchdog
116	timer.  This driver implements the standard Linux watchdog timer
117	interface on top of the IPMI message handler.
118	
119	ipmi_poweroff - Some systems support the ability to be turned off via
120	IPMI commands.
121	
122	bt-bmc - This is not part of the main driver, but instead a driver for
123	accessing a BMC-side interface of a BT interface.  It is used on BMCs
124	running Linux to provide an interface to the host.
125	
126	These are all individually selectable via configuration options.
127	
128	Much documentation for the interface is in the include files.  The
129	IPMI include files are:
130	
131	linux/ipmi.h - Contains the user interface and IOCTL interface for IPMI.
132	
133	linux/ipmi_smi.h - Contains the interface for system management interfaces
134	(things that interface to IPMI controllers) to use.
135	
136	linux/ipmi_msgdefs.h - General definitions for base IPMI messaging.
137	
138	
139	Addressing
140	----------
141	
142	The IPMI addressing works much like IP addresses, you have an overlay
143	to handle the different address types.  The overlay is::
144	
145	  struct ipmi_addr
146	  {
147		int   addr_type;
148		short channel;
149		char  data[IPMI_MAX_ADDR_SIZE];
150	  };
151	
152	The addr_type determines what the address really is.  The driver
153	currently understands two different types of addresses.
154	
155	"System Interface" addresses are defined as::
156	
157	  struct ipmi_system_interface_addr
158	  {
159		int   addr_type;
160		short channel;
161	  };
162	
163	and the type is IPMI_SYSTEM_INTERFACE_ADDR_TYPE.  This is used for talking
164	straight to the BMC on the current card.  The channel must be
165	IPMI_BMC_CHANNEL.
166	
167	Messages that are destined to go out on the IPMB bus use the
168	IPMI_IPMB_ADDR_TYPE address type.  The format is::
169	
170	  struct ipmi_ipmb_addr
171	  {
172		int           addr_type;
173		short         channel;
174		unsigned char slave_addr;
175		unsigned char lun;
176	  };
177	
178	The "channel" here is generally zero, but some devices support more
179	than one channel, it corresponds to the channel as defined in the IPMI
180	spec.
181	
182	
183	Messages
184	--------
185	
186	Messages are defined as::
187	
188	  struct ipmi_msg
189	  {
190		unsigned char netfn;
191		unsigned char lun;
192		unsigned char cmd;
193		unsigned char *data;
194		int           data_len;
195	  };
196	
197	The driver takes care of adding/stripping the header information.  The
198	data portion is just the data to be send (do NOT put addressing info
199	here) or the response.  Note that the completion code of a response is
200	the first item in "data", it is not stripped out because that is how
201	all the messages are defined in the spec (and thus makes counting the
202	offsets a little easier :-).
203	
204	When using the IOCTL interface from userland, you must provide a block
205	of data for "data", fill it, and set data_len to the length of the
206	block of data, even when receiving messages.  Otherwise the driver
207	will have no place to put the message.
208	
209	Messages coming up from the message handler in kernelland will come in
210	as::
211	
212	  struct ipmi_recv_msg
213	  {
214		struct list_head link;
215	
216		/* The type of message as defined in the "Receive Types"
217	           defines above. */
218		int         recv_type;
219	
220		ipmi_user_t      *user;
221		struct ipmi_addr addr;
222		long             msgid;
223		struct ipmi_msg  msg;
224	
225		/* Call this when done with the message.  It will presumably free
226		   the message and do any other necessary cleanup. */
227		void (*done)(struct ipmi_recv_msg *msg);
228	
229		/* Place-holder for the data, don't make any assumptions about
230		   the size or existence of this, since it may change. */
231		unsigned char   msg_data[IPMI_MAX_MSG_LENGTH];
232	  };
233	
234	You should look at the receive type and handle the message
235	appropriately.
236	
237	
238	The Upper Layer Interface (Message Handler)
239	-------------------------------------------
240	
241	The upper layer of the interface provides the users with a consistent
242	view of the IPMI interfaces.  It allows multiple SMI interfaces to be
243	addressed (because some boards actually have multiple BMCs on them)
244	and the user should not have to care what type of SMI is below them.
245	
246	
247	Watching For Interfaces
248	^^^^^^^^^^^^^^^^^^^^^^^
249	
250	When your code comes up, the IPMI driver may or may not have detected
251	if IPMI devices exist.  So you might have to defer your setup until
252	the device is detected, or you might be able to do it immediately.
253	To handle this, and to allow for discovery, you register an SMI
254	watcher with ipmi_smi_watcher_register() to iterate over interfaces
255	and tell you when they come and go.
256	
257	
258	Creating the User
259	^^^^^^^^^^^^^^^^^
260	
261	To use the message handler, you must first create a user using
262	ipmi_create_user.  The interface number specifies which SMI you want
263	to connect to, and you must supply callback functions to be called
264	when data comes in.  The callback function can run at interrupt level,
265	so be careful using the callbacks.  This also allows to you pass in a
266	piece of data, the handler_data, that will be passed back to you on
267	all calls.
268	
269	Once you are done, call ipmi_destroy_user() to get rid of the user.
270	
271	From userland, opening the device automatically creates a user, and
272	closing the device automatically destroys the user.
273	
274	
275	Messaging
276	^^^^^^^^^
277	
278	To send a message from kernel-land, the ipmi_request_settime() call does
279	pretty much all message handling.  Most of the parameter are
280	self-explanatory.  However, it takes a "msgid" parameter.  This is NOT
281	the sequence number of messages.  It is simply a long value that is
282	passed back when the response for the message is returned.  You may
283	use it for anything you like.
284	
285	Responses come back in the function pointed to by the ipmi_recv_hndl
286	field of the "handler" that you passed in to ipmi_create_user().
287	Remember again, these may be running at interrupt level.  Remember to
288	look at the receive type, too.
289	
290	From userland, you fill out an ipmi_req_t structure and use the
291	IPMICTL_SEND_COMMAND ioctl.  For incoming stuff, you can use select()
292	or poll() to wait for messages to come in.  However, you cannot use
293	read() to get them, you must call the IPMICTL_RECEIVE_MSG with the
294	ipmi_recv_t structure to actually get the message.  Remember that you
295	must supply a pointer to a block of data in the msg.data field, and
296	you must fill in the msg.data_len field with the size of the data.
297	This gives the receiver a place to actually put the message.
298	
299	If the message cannot fit into the data you provide, you will get an
300	EMSGSIZE error and the driver will leave the data in the receive
301	queue.  If you want to get it and have it truncate the message, us
302	the IPMICTL_RECEIVE_MSG_TRUNC ioctl.
303	
304	When you send a command (which is defined by the lowest-order bit of
305	the netfn per the IPMI spec) on the IPMB bus, the driver will
306	automatically assign the sequence number to the command and save the
307	command.  If the response is not receive in the IPMI-specified 5
308	seconds, it will generate a response automatically saying the command
309	timed out.  If an unsolicited response comes in (if it was after 5
310	seconds, for instance), that response will be ignored.
311	
312	In kernelland, after you receive a message and are done with it, you
313	MUST call ipmi_free_recv_msg() on it, or you will leak messages.  Note
314	that you should NEVER mess with the "done" field of a message, that is
315	required to properly clean up the message.
316	
317	Note that when sending, there is an ipmi_request_supply_msgs() call
318	that lets you supply the smi and receive message.  This is useful for
319	pieces of code that need to work even if the system is out of buffers
320	(the watchdog timer uses this, for instance).  You supply your own
321	buffer and own free routines.  This is not recommended for normal use,
322	though, since it is tricky to manage your own buffers.
323	
324	
325	Events and Incoming Commands
326	^^^^^^^^^^^^^^^^^^^^^^^^^^^^
327	
328	The driver takes care of polling for IPMI events and receiving
329	commands (commands are messages that are not responses, they are
330	commands that other things on the IPMB bus have sent you).  To receive
331	these, you must register for them, they will not automatically be sent
332	to you.
333	
334	To receive events, you must call ipmi_set_gets_events() and set the
335	"val" to non-zero.  Any events that have been received by the driver
336	since startup will immediately be delivered to the first user that
337	registers for events.  After that, if multiple users are registered
338	for events, they will all receive all events that come in.
339	
340	For receiving commands, you have to individually register commands you
341	want to receive.  Call ipmi_register_for_cmd() and supply the netfn
342	and command name for each command you want to receive.  You also
343	specify a bitmask of the channels you want to receive the command from
344	(or use IPMI_CHAN_ALL for all channels if you don't care).  Only one
345	user may be registered for each netfn/cmd/channel, but different users
346	may register for different commands, or the same command if the
347	channel bitmasks do not overlap.
348	
349	From userland, equivalent IOCTLs are provided to do these functions.
350	
351	
352	The Lower Layer (SMI) Interface
353	-------------------------------
354	
355	As mentioned before, multiple SMI interfaces may be registered to the
356	message handler, each of these is assigned an interface number when
357	they register with the message handler.  They are generally assigned
358	in the order they register, although if an SMI unregisters and then
359	another one registers, all bets are off.
360	
361	The ipmi_smi.h defines the interface for management interfaces, see
362	that for more details.
363	
364	
365	The SI Driver
366	-------------
367	
368	The SI driver allows KCS, BT, and SMIC interfaces to be configured
369	in the system.  It discovers interfaces through a host of different
370	methods, depending on the system.
371	
372	You can specify up to four interfaces on the module load line and
373	control some module parameters::
374	
375	  modprobe ipmi_si.o type=<type1>,<type2>....
376	       ports=<port1>,<port2>... addrs=<addr1>,<addr2>...
377	       irqs=<irq1>,<irq2>...
378	       regspacings=<sp1>,<sp2>,... regsizes=<size1>,<size2>,...
379	       regshifts=<shift1>,<shift2>,...
380	       slave_addrs=<addr1>,<addr2>,...
381	       force_kipmid=<enable1>,<enable2>,...
382	       kipmid_max_busy_us=<ustime1>,<ustime2>,...
383	       unload_when_empty=[0|1]
384	       trydmi=[0|1] tryacpi=[0|1]
385	       tryplatform=[0|1] trypci=[0|1]
386	
387	Each of these except try... items is a list, the first item for the
388	first interface, second item for the second interface, etc.
389	
390	The si_type may be either "kcs", "smic", or "bt".  If you leave it blank, it
391	defaults to "kcs".
392	
393	If you specify addrs as non-zero for an interface, the driver will
394	use the memory address given as the address of the device.  This
395	overrides si_ports.
396	
397	If you specify ports as non-zero for an interface, the driver will
398	use the I/O port given as the device address.
399	
400	If you specify irqs as non-zero for an interface, the driver will
401	attempt to use the given interrupt for the device.
402	
403	The other try... items disable discovery by their corresponding
404	names.  These are all enabled by default, set them to zero to disable
405	them.  The tryplatform disables openfirmware.
406	
407	The next three parameters have to do with register layout.  The
408	registers used by the interfaces may not appear at successive
409	locations and they may not be in 8-bit registers.  These parameters
410	allow the layout of the data in the registers to be more precisely
411	specified.
412	
413	The regspacings parameter give the number of bytes between successive
414	register start addresses.  For instance, if the regspacing is set to 4
415	and the start address is 0xca2, then the address for the second
416	register would be 0xca6.  This defaults to 1.
417	
418	The regsizes parameter gives the size of a register, in bytes.  The
419	data used by IPMI is 8-bits wide, but it may be inside a larger
420	register.  This parameter allows the read and write type to specified.
421	It may be 1, 2, 4, or 8.  The default is 1.
422	
423	Since the register size may be larger than 32 bits, the IPMI data may not
424	be in the lower 8 bits.  The regshifts parameter give the amount to shift
425	the data to get to the actual IPMI data.
426	
427	The slave_addrs specifies the IPMI address of the local BMC.  This is
428	usually 0x20 and the driver defaults to that, but in case it's not, it
429	can be specified when the driver starts up.
430	
431	The force_ipmid parameter forcefully enables (if set to 1) or disables
432	(if set to 0) the kernel IPMI daemon.  Normally this is auto-detected
433	by the driver, but systems with broken interrupts might need an enable,
434	or users that don't want the daemon (don't need the performance, don't
435	want the CPU hit) can disable it.
436	
437	If unload_when_empty is set to 1, the driver will be unloaded if it
438	doesn't find any interfaces or all the interfaces fail to work.  The
439	default is one.  Setting to 0 is useful with the hotmod, but is
440	obviously only useful for modules.
441	
442	When compiled into the kernel, the parameters can be specified on the
443	kernel command line as::
444	
445	  ipmi_si.type=<type1>,<type2>...
446	       ipmi_si.ports=<port1>,<port2>... ipmi_si.addrs=<addr1>,<addr2>...
447	       ipmi_si.irqs=<irq1>,<irq2>...
448	       ipmi_si.regspacings=<sp1>,<sp2>,...
449	       ipmi_si.regsizes=<size1>,<size2>,...
450	       ipmi_si.regshifts=<shift1>,<shift2>,...
451	       ipmi_si.slave_addrs=<addr1>,<addr2>,...
452	       ipmi_si.force_kipmid=<enable1>,<enable2>,...
453	       ipmi_si.kipmid_max_busy_us=<ustime1>,<ustime2>,...
454	
455	It works the same as the module parameters of the same names.
456	
457	If your IPMI interface does not support interrupts and is a KCS or
458	SMIC interface, the IPMI driver will start a kernel thread for the
459	interface to help speed things up.  This is a low-priority kernel
460	thread that constantly polls the IPMI driver while an IPMI operation
461	is in progress.  The force_kipmid module parameter will all the user to
462	force this thread on or off.  If you force it off and don't have
463	interrupts, the driver will run VERY slowly.  Don't blame me,
464	these interfaces suck.
465	
466	Unfortunately, this thread can use a lot of CPU depending on the
467	interface's performance.  This can waste a lot of CPU and cause
468	various issues with detecting idle CPU and using extra power.  To
469	avoid this, the kipmid_max_busy_us sets the maximum amount of time, in
470	microseconds, that kipmid will spin before sleeping for a tick.  This
471	value sets a balance between performance and CPU waste and needs to be
472	tuned to your needs.  Maybe, someday, auto-tuning will be added, but
473	that's not a simple thing and even the auto-tuning would need to be
474	tuned to the user's desired performance.
475	
476	The driver supports a hot add and remove of interfaces.  This way,
477	interfaces can be added or removed after the kernel is up and running.
478	This is done using /sys/modules/ipmi_si/parameters/hotmod, which is a
479	write-only parameter.  You write a string to this interface.  The string
480	has the format::
481	
482	   <op1>[:op2[:op3...]]
483	
484	The "op"s are::
485	
486	   add|remove,kcs|bt|smic,mem|i/o,<address>[,<opt1>[,<opt2>[,...]]]
487	
488	You can specify more than one interface on the line.  The "opt"s are::
489	
490	   rsp=<regspacing>
491	   rsi=<regsize>
492	   rsh=<regshift>
493	   irq=<irq>
494	   ipmb=<ipmb slave addr>
495	
496	and these have the same meanings as discussed above.  Note that you
497	can also use this on the kernel command line for a more compact format
498	for specifying an interface.  Note that when removing an interface,
499	only the first three parameters (si type, address type, and address)
500	are used for the comparison.  Any options are ignored for removing.
501	
502	The SMBus Driver (SSIF)
503	-----------------------
504	
505	The SMBus driver allows up to 4 SMBus devices to be configured in the
506	system.  By default, the driver will only register with something it
507	finds in DMI or ACPI tables.  You can change this
508	at module load time (for a module) with::
509	
510	  modprobe ipmi_ssif.o
511		addr=<i2caddr1>[,<i2caddr2>[,...]]
512		adapter=<adapter1>[,<adapter2>[...]]
513		dbg=<flags1>,<flags2>...
514		slave_addrs=<addr1>,<addr2>,...
515		tryacpi=[0|1] trydmi=[0|1]
516		[dbg_probe=1]
517	
518	The addresses are normal I2C addresses.  The adapter is the string
519	name of the adapter, as shown in /sys/class/i2c-adapter/i2c-<n>/name.
520	It is *NOT* i2c-<n> itself.  Also, the comparison is done ignoring
521	spaces, so if the name is "This is an I2C chip" you can say
522	adapter_name=ThisisanI2cchip.  This is because it's hard to pass in
523	spaces in kernel parameters.
524	
525	The debug flags are bit flags for each BMC found, they are:
526	IPMI messages: 1, driver state: 2, timing: 4, I2C probe: 8
527	
528	The tryxxx parameters can be used to disable detecting interfaces
529	from various sources.
530	
531	Setting dbg_probe to 1 will enable debugging of the probing and
532	detection process for BMCs on the SMBusses.
533	
534	The slave_addrs specifies the IPMI address of the local BMC.  This is
535	usually 0x20 and the driver defaults to that, but in case it's not, it
536	can be specified when the driver starts up.
537	
538	Discovering the IPMI compliant BMC on the SMBus can cause devices on
539	the I2C bus to fail. The SMBus driver writes a "Get Device ID" IPMI
540	message as a block write to the I2C bus and waits for a response.
541	This action can be detrimental to some I2C devices. It is highly
542	recommended that the known I2C address be given to the SMBus driver in
543	the smb_addr parameter unless you have DMI or ACPI data to tell the
544	driver what to use.
545	
546	When compiled into the kernel, the addresses can be specified on the
547	kernel command line as::
548	
549	  ipmb_ssif.addr=<i2caddr1>[,<i2caddr2>[...]]
550		ipmi_ssif.adapter=<adapter1>[,<adapter2>[...]]
551		ipmi_ssif.dbg=<flags1>[,<flags2>[...]]
552		ipmi_ssif.dbg_probe=1
553		ipmi_ssif.slave_addrs=<addr1>[,<addr2>[...]]
554		ipmi_ssif.tryacpi=[0|1] ipmi_ssif.trydmi=[0|1]
555	
556	These are the same options as on the module command line.
557	
558	The I2C driver does not support non-blocking access or polling, so
559	this driver cannod to IPMI panic events, extend the watchdog at panic
560	time, or other panic-related IPMI functions without special kernel
561	patches and driver modifications.  You can get those at the openipmi
562	web page.
563	
564	The driver supports a hot add and remove of interfaces through the I2C
565	sysfs interface.
566	
567	Other Pieces
568	------------
569	
570	Get the detailed info related with the IPMI device
571	--------------------------------------------------
572	
573	Some users need more detailed information about a device, like where
574	the address came from or the raw base device for the IPMI interface.
575	You can use the IPMI smi_watcher to catch the IPMI interfaces as they
576	come or go, and to grab the information, you can use the function
577	ipmi_get_smi_info(), which returns the following structure::
578	
579	  struct ipmi_smi_info {
580		enum ipmi_addr_src addr_src;
581		struct device *dev;
582		union {
583			struct {
584				void *acpi_handle;
585			} acpi_info;
586		} addr_info;
587	  };
588	
589	Currently special info for only for SI_ACPI address sources is
590	returned.  Others may be added as necessary.
591	
592	Note that the dev pointer is included in the above structure, and
593	assuming ipmi_smi_get_info returns success, you must call put_device
594	on the dev pointer.
595	
596	
597	Watchdog
598	--------
599	
600	A watchdog timer is provided that implements the Linux-standard
601	watchdog timer interface.  It has three module parameters that can be
602	used to control it::
603	
604	  modprobe ipmi_watchdog timeout=<t> pretimeout=<t> action=<action type>
605	      preaction=<preaction type> preop=<preop type> start_now=x
606	      nowayout=x ifnum_to_use=n panic_wdt_timeout=<t>
607	
608	ifnum_to_use specifies which interface the watchdog timer should use.
609	The default is -1, which means to pick the first one registered.
610	
611	The timeout is the number of seconds to the action, and the pretimeout
612	is the amount of seconds before the reset that the pre-timeout panic will
613	occur (if pretimeout is zero, then pretimeout will not be enabled).  Note
614	that the pretimeout is the time before the final timeout.  So if the
615	timeout is 50 seconds and the pretimeout is 10 seconds, then the pretimeout
616	will occur in 40 second (10 seconds before the timeout). The panic_wdt_timeout
617	is the value of timeout which is set on kernel panic, in order to let actions
618	such as kdump to occur during panic.
619	
620	The action may be "reset", "power_cycle", or "power_off", and
621	specifies what to do when the timer times out, and defaults to
622	"reset".
623	
624	The preaction may be "pre_smi" for an indication through the SMI
625	interface, "pre_int" for an indication through the SMI with an
626	interrupts, and "pre_nmi" for a NMI on a preaction.  This is how
627	the driver is informed of the pretimeout.
628	
629	The preop may be set to "preop_none" for no operation on a pretimeout,
630	"preop_panic" to set the preoperation to panic, or "preop_give_data"
631	to provide data to read from the watchdog device when the pretimeout
632	occurs.  A "pre_nmi" setting CANNOT be used with "preop_give_data"
633	because you can't do data operations from an NMI.
634	
635	When preop is set to "preop_give_data", one byte comes ready to read
636	on the device when the pretimeout occurs.  Select and fasync work on
637	the device, as well.
638	
639	If start_now is set to 1, the watchdog timer will start running as
640	soon as the driver is loaded.
641	
642	If nowayout is set to 1, the watchdog timer will not stop when the
643	watchdog device is closed.  The default value of nowayout is true
644	if the CONFIG_WATCHDOG_NOWAYOUT option is enabled, or false if not.
645	
646	When compiled into the kernel, the kernel command line is available
647	for configuring the watchdog::
648	
649	  ipmi_watchdog.timeout=<t> ipmi_watchdog.pretimeout=<t>
650		ipmi_watchdog.action=<action type>
651		ipmi_watchdog.preaction=<preaction type>
652		ipmi_watchdog.preop=<preop type>
653		ipmi_watchdog.start_now=x
654		ipmi_watchdog.nowayout=x
655		ipmi_watchdog.panic_wdt_timeout=<t>
656	
657	The options are the same as the module parameter options.
658	
659	The watchdog will panic and start a 120 second reset timeout if it
660	gets a pre-action.  During a panic or a reboot, the watchdog will
661	start a 120 timer if it is running to make sure the reboot occurs.
662	
663	Note that if you use the NMI preaction for the watchdog, you MUST NOT
664	use the nmi watchdog.  There is no reasonable way to tell if an NMI
665	comes from the IPMI controller, so it must assume that if it gets an
666	otherwise unhandled NMI, it must be from IPMI and it will panic
667	immediately.
668	
669	Once you open the watchdog timer, you must write a 'V' character to the
670	device to close it, or the timer will not stop.  This is a new semantic
671	for the driver, but makes it consistent with the rest of the watchdog
672	drivers in Linux.
673	
674	
675	Panic Timeouts
676	--------------
677	
678	The OpenIPMI driver supports the ability to put semi-custom and custom
679	events in the system event log if a panic occurs.  if you enable the
680	'Generate a panic event to all BMCs on a panic' option, you will get
681	one event on a panic in a standard IPMI event format.  If you enable
682	the 'Generate OEM events containing the panic string' option, you will
683	also get a bunch of OEM events holding the panic string.
684	
685	
686	The field settings of the events are:
687	
688	* Generator ID: 0x21 (kernel)
689	* EvM Rev: 0x03 (this event is formatting in IPMI 1.0 format)
690	* Sensor Type: 0x20 (OS critical stop sensor)
691	* Sensor #: The first byte of the panic string (0 if no panic string)
692	* Event Dir | Event Type: 0x6f (Assertion, sensor-specific event info)
693	* Event Data 1: 0xa1 (Runtime stop in OEM bytes 2 and 3)
694	* Event data 2: second byte of panic string
695	* Event data 3: third byte of panic string
696	
697	See the IPMI spec for the details of the event layout.  This event is
698	always sent to the local management controller.  It will handle routing
699	the message to the right place
700	
701	Other OEM events have the following format:
702	
703	* Record ID (bytes 0-1): Set by the SEL.
704	* Record type (byte 2): 0xf0 (OEM non-timestamped)
705	* byte 3: The slave address of the card saving the panic
706	* byte 4: A sequence number (starting at zero)
707	  The rest of the bytes (11 bytes) are the panic string.  If the panic string
708	  is longer than 11 bytes, multiple messages will be sent with increasing
709	  sequence numbers.
710	
711	Because you cannot send OEM events using the standard interface, this
712	function will attempt to find an SEL and add the events there.  It
713	will first query the capabilities of the local management controller.
714	If it has an SEL, then they will be stored in the SEL of the local
715	management controller.  If not, and the local management controller is
716	an event generator, the event receiver from the local management
717	controller will be queried and the events sent to the SEL on that
718	device.  Otherwise, the events go nowhere since there is nowhere to
719	send them.
720	
721	
722	Poweroff
723	--------
724	
725	If the poweroff capability is selected, the IPMI driver will install
726	a shutdown function into the standard poweroff function pointer.  This
727	is in the ipmi_poweroff module.  When the system requests a powerdown,
728	it will send the proper IPMI commands to do this.  This is supported on
729	several platforms.
730	
731	There is a module parameter named "poweroff_powercycle" that may
732	either be zero (do a power down) or non-zero (do a power cycle, power
733	the system off, then power it on in a few seconds).  Setting
734	ipmi_poweroff.poweroff_control=x will do the same thing on the kernel
735	command line.  The parameter is also available via the proc filesystem
736	in /proc/sys/dev/ipmi/poweroff_powercycle.  Note that if the system
737	does not support power cycling, it will always do the power off.
738	
739	The "ifnum_to_use" parameter specifies which interface the poweroff
740	code should use.  The default is -1, which means to pick the first one
741	registered.
742	
743	Note that if you have ACPI enabled, the system will prefer using ACPI to
744	power off.
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