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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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.  You can also enable these dynamically by setting the module
85	parameter named "panic_op" in the ipmi_msghandler module to "event"
86	or "string".  Setting that parameter to "none" disables this function.
87	
88	Basic Design
89	------------
90	
91	The Linux IPMI driver is designed to be very modular and flexible, you
92	only need to take the pieces you need and you can use it in many
93	different ways.  Because of that, it's broken into many chunks of
94	code.  These chunks (by module name) are:
95	
96	ipmi_msghandler - This is the central piece of software for the IPMI
97	system.  It handles all messages, message timing, and responses.  The
98	IPMI users tie into this, and the IPMI physical interfaces (called
99	System Management Interfaces, or SMIs) also tie in here.  This
100	provides the kernelland interface for IPMI, but does not provide an
101	interface for use by application processes.
102	
103	ipmi_devintf - This provides a userland IOCTL interface for the IPMI
104	driver, each open file for this device ties in to the message handler
105	as an IPMI user.
106	
107	ipmi_si - A driver for various system interfaces.  This supports KCS,
108	SMIC, and BT interfaces.  Unless you have an SMBus interface or your
109	own custom interface, you probably need to use this.
110	
111	ipmi_ssif - A driver for accessing BMCs on the SMBus. It uses the
112	I2C kernel driver's SMBus interfaces to send and receive IPMI messages
113	over the SMBus.
114	
115	ipmi_powernv - A driver for access BMCs on POWERNV systems.
116	
117	ipmi_watchdog - IPMI requires systems to have a very capable watchdog
118	timer.  This driver implements the standard Linux watchdog timer
119	interface on top of the IPMI message handler.
120	
121	ipmi_poweroff - Some systems support the ability to be turned off via
122	IPMI commands.
123	
124	bt-bmc - This is not part of the main driver, but instead a driver for
125	accessing a BMC-side interface of a BT interface.  It is used on BMCs
126	running Linux to provide an interface to the host.
127	
128	These are all individually selectable via configuration options.
129	
130	Much documentation for the interface is in the include files.  The
131	IPMI include files are:
132	
133	linux/ipmi.h - Contains the user interface and IOCTL interface for IPMI.
134	
135	linux/ipmi_smi.h - Contains the interface for system management interfaces
136	(things that interface to IPMI controllers) to use.
137	
138	linux/ipmi_msgdefs.h - General definitions for base IPMI messaging.
139	
140	
141	Addressing
142	----------
143	
144	The IPMI addressing works much like IP addresses, you have an overlay
145	to handle the different address types.  The overlay is::
146	
147	  struct ipmi_addr
148	  {
149		int   addr_type;
150		short channel;
151		char  data[IPMI_MAX_ADDR_SIZE];
152	  };
153	
154	The addr_type determines what the address really is.  The driver
155	currently understands two different types of addresses.
156	
157	"System Interface" addresses are defined as::
158	
159	  struct ipmi_system_interface_addr
160	  {
161		int   addr_type;
162		short channel;
163	  };
164	
165	and the type is IPMI_SYSTEM_INTERFACE_ADDR_TYPE.  This is used for talking
166	straight to the BMC on the current card.  The channel must be
167	IPMI_BMC_CHANNEL.
168	
169	Messages that are destined to go out on the IPMB bus use the
170	IPMI_IPMB_ADDR_TYPE address type.  The format is::
171	
172	  struct ipmi_ipmb_addr
173	  {
174		int           addr_type;
175		short         channel;
176		unsigned char slave_addr;
177		unsigned char lun;
178	  };
179	
180	The "channel" here is generally zero, but some devices support more
181	than one channel, it corresponds to the channel as defined in the IPMI
182	spec.
183	
184	
185	Messages
186	--------
187	
188	Messages are defined as::
189	
190	  struct ipmi_msg
191	  {
192		unsigned char netfn;
193		unsigned char lun;
194		unsigned char cmd;
195		unsigned char *data;
196		int           data_len;
197	  };
198	
199	The driver takes care of adding/stripping the header information.  The
200	data portion is just the data to be send (do NOT put addressing info
201	here) or the response.  Note that the completion code of a response is
202	the first item in "data", it is not stripped out because that is how
203	all the messages are defined in the spec (and thus makes counting the
204	offsets a little easier :-).
205	
206	When using the IOCTL interface from userland, you must provide a block
207	of data for "data", fill it, and set data_len to the length of the
208	block of data, even when receiving messages.  Otherwise the driver
209	will have no place to put the message.
210	
211	Messages coming up from the message handler in kernelland will come in
212	as::
213	
214	  struct ipmi_recv_msg
215	  {
216		struct list_head link;
217	
218		/* The type of message as defined in the "Receive Types"
219	           defines above. */
220		int         recv_type;
221	
222		ipmi_user_t      *user;
223		struct ipmi_addr addr;
224		long             msgid;
225		struct ipmi_msg  msg;
226	
227		/* Call this when done with the message.  It will presumably free
228		   the message and do any other necessary cleanup. */
229		void (*done)(struct ipmi_recv_msg *msg);
230	
231		/* Place-holder for the data, don't make any assumptions about
232		   the size or existence of this, since it may change. */
233		unsigned char   msg_data[IPMI_MAX_MSG_LENGTH];
234	  };
235	
236	You should look at the receive type and handle the message
237	appropriately.
238	
239	
240	The Upper Layer Interface (Message Handler)
241	-------------------------------------------
242	
243	The upper layer of the interface provides the users with a consistent
244	view of the IPMI interfaces.  It allows multiple SMI interfaces to be
245	addressed (because some boards actually have multiple BMCs on them)
246	and the user should not have to care what type of SMI is below them.
247	
248	
249	Watching For Interfaces
250	^^^^^^^^^^^^^^^^^^^^^^^
251	
252	When your code comes up, the IPMI driver may or may not have detected
253	if IPMI devices exist.  So you might have to defer your setup until
254	the device is detected, or you might be able to do it immediately.
255	To handle this, and to allow for discovery, you register an SMI
256	watcher with ipmi_smi_watcher_register() to iterate over interfaces
257	and tell you when they come and go.
258	
259	
260	Creating the User
261	^^^^^^^^^^^^^^^^^
262	
263	To use the message handler, you must first create a user using
264	ipmi_create_user.  The interface number specifies which SMI you want
265	to connect to, and you must supply callback functions to be called
266	when data comes in.  The callback function can run at interrupt level,
267	so be careful using the callbacks.  This also allows to you pass in a
268	piece of data, the handler_data, that will be passed back to you on
269	all calls.
270	
271	Once you are done, call ipmi_destroy_user() to get rid of the user.
272	
273	From userland, opening the device automatically creates a user, and
274	closing the device automatically destroys the user.
275	
276	
277	Messaging
278	^^^^^^^^^
279	
280	To send a message from kernel-land, the ipmi_request_settime() call does
281	pretty much all message handling.  Most of the parameter are
282	self-explanatory.  However, it takes a "msgid" parameter.  This is NOT
283	the sequence number of messages.  It is simply a long value that is
284	passed back when the response for the message is returned.  You may
285	use it for anything you like.
286	
287	Responses come back in the function pointed to by the ipmi_recv_hndl
288	field of the "handler" that you passed in to ipmi_create_user().
289	Remember again, these may be running at interrupt level.  Remember to
290	look at the receive type, too.
291	
292	From userland, you fill out an ipmi_req_t structure and use the
293	IPMICTL_SEND_COMMAND ioctl.  For incoming stuff, you can use select()
294	or poll() to wait for messages to come in.  However, you cannot use
295	read() to get them, you must call the IPMICTL_RECEIVE_MSG with the
296	ipmi_recv_t structure to actually get the message.  Remember that you
297	must supply a pointer to a block of data in the msg.data field, and
298	you must fill in the msg.data_len field with the size of the data.
299	This gives the receiver a place to actually put the message.
300	
301	If the message cannot fit into the data you provide, you will get an
302	EMSGSIZE error and the driver will leave the data in the receive
303	queue.  If you want to get it and have it truncate the message, us
304	the IPMICTL_RECEIVE_MSG_TRUNC ioctl.
305	
306	When you send a command (which is defined by the lowest-order bit of
307	the netfn per the IPMI spec) on the IPMB bus, the driver will
308	automatically assign the sequence number to the command and save the
309	command.  If the response is not receive in the IPMI-specified 5
310	seconds, it will generate a response automatically saying the command
311	timed out.  If an unsolicited response comes in (if it was after 5
312	seconds, for instance), that response will be ignored.
313	
314	In kernelland, after you receive a message and are done with it, you
315	MUST call ipmi_free_recv_msg() on it, or you will leak messages.  Note
316	that you should NEVER mess with the "done" field of a message, that is
317	required to properly clean up the message.
318	
319	Note that when sending, there is an ipmi_request_supply_msgs() call
320	that lets you supply the smi and receive message.  This is useful for
321	pieces of code that need to work even if the system is out of buffers
322	(the watchdog timer uses this, for instance).  You supply your own
323	buffer and own free routines.  This is not recommended for normal use,
324	though, since it is tricky to manage your own buffers.
325	
326	
327	Events and Incoming Commands
328	^^^^^^^^^^^^^^^^^^^^^^^^^^^^
329	
330	The driver takes care of polling for IPMI events and receiving
331	commands (commands are messages that are not responses, they are
332	commands that other things on the IPMB bus have sent you).  To receive
333	these, you must register for them, they will not automatically be sent
334	to you.
335	
336	To receive events, you must call ipmi_set_gets_events() and set the
337	"val" to non-zero.  Any events that have been received by the driver
338	since startup will immediately be delivered to the first user that
339	registers for events.  After that, if multiple users are registered
340	for events, they will all receive all events that come in.
341	
342	For receiving commands, you have to individually register commands you
343	want to receive.  Call ipmi_register_for_cmd() and supply the netfn
344	and command name for each command you want to receive.  You also
345	specify a bitmask of the channels you want to receive the command from
346	(or use IPMI_CHAN_ALL for all channels if you don't care).  Only one
347	user may be registered for each netfn/cmd/channel, but different users
348	may register for different commands, or the same command if the
349	channel bitmasks do not overlap.
350	
351	From userland, equivalent IOCTLs are provided to do these functions.
352	
353	
354	The Lower Layer (SMI) Interface
355	-------------------------------
356	
357	As mentioned before, multiple SMI interfaces may be registered to the
358	message handler, each of these is assigned an interface number when
359	they register with the message handler.  They are generally assigned
360	in the order they register, although if an SMI unregisters and then
361	another one registers, all bets are off.
362	
363	The ipmi_smi.h defines the interface for management interfaces, see
364	that for more details.
365	
366	
367	The SI Driver
368	-------------
369	
370	The SI driver allows KCS, BT, and SMIC interfaces to be configured
371	in the system.  It discovers interfaces through a host of different
372	methods, depending on the system.
373	
374	You can specify up to four interfaces on the module load line and
375	control some module parameters::
376	
377	  modprobe ipmi_si.o type=<type1>,<type2>....
378	       ports=<port1>,<port2>... addrs=<addr1>,<addr2>...
379	       irqs=<irq1>,<irq2>...
380	       regspacings=<sp1>,<sp2>,... regsizes=<size1>,<size2>,...
381	       regshifts=<shift1>,<shift2>,...
382	       slave_addrs=<addr1>,<addr2>,...
383	       force_kipmid=<enable1>,<enable2>,...
384	       kipmid_max_busy_us=<ustime1>,<ustime2>,...
385	       unload_when_empty=[0|1]
386	       trydmi=[0|1] tryacpi=[0|1]
387	       tryplatform=[0|1] trypci=[0|1]
388	
389	Each of these except try... items is a list, the first item for the
390	first interface, second item for the second interface, etc.
391	
392	The si_type may be either "kcs", "smic", or "bt".  If you leave it blank, it
393	defaults to "kcs".
394	
395	If you specify addrs as non-zero for an interface, the driver will
396	use the memory address given as the address of the device.  This
397	overrides si_ports.
398	
399	If you specify ports as non-zero for an interface, the driver will
400	use the I/O port given as the device address.
401	
402	If you specify irqs as non-zero for an interface, the driver will
403	attempt to use the given interrupt for the device.
404	
405	The other try... items disable discovery by their corresponding
406	names.  These are all enabled by default, set them to zero to disable
407	them.  The tryplatform disables openfirmware.
408	
409	The next three parameters have to do with register layout.  The
410	registers used by the interfaces may not appear at successive
411	locations and they may not be in 8-bit registers.  These parameters
412	allow the layout of the data in the registers to be more precisely
413	specified.
414	
415	The regspacings parameter give the number of bytes between successive
416	register start addresses.  For instance, if the regspacing is set to 4
417	and the start address is 0xca2, then the address for the second
418	register would be 0xca6.  This defaults to 1.
419	
420	The regsizes parameter gives the size of a register, in bytes.  The
421	data used by IPMI is 8-bits wide, but it may be inside a larger
422	register.  This parameter allows the read and write type to specified.
423	It may be 1, 2, 4, or 8.  The default is 1.
424	
425	Since the register size may be larger than 32 bits, the IPMI data may not
426	be in the lower 8 bits.  The regshifts parameter give the amount to shift
427	the data to get to the actual IPMI data.
428	
429	The slave_addrs specifies the IPMI address of the local BMC.  This is
430	usually 0x20 and the driver defaults to that, but in case it's not, it
431	can be specified when the driver starts up.
432	
433	The force_ipmid parameter forcefully enables (if set to 1) or disables
434	(if set to 0) the kernel IPMI daemon.  Normally this is auto-detected
435	by the driver, but systems with broken interrupts might need an enable,
436	or users that don't want the daemon (don't need the performance, don't
437	want the CPU hit) can disable it.
438	
439	If unload_when_empty is set to 1, the driver will be unloaded if it
440	doesn't find any interfaces or all the interfaces fail to work.  The
441	default is one.  Setting to 0 is useful with the hotmod, but is
442	obviously only useful for modules.
443	
444	When compiled into the kernel, the parameters can be specified on the
445	kernel command line as::
446	
447	  ipmi_si.type=<type1>,<type2>...
448	       ipmi_si.ports=<port1>,<port2>... ipmi_si.addrs=<addr1>,<addr2>...
449	       ipmi_si.irqs=<irq1>,<irq2>...
450	       ipmi_si.regspacings=<sp1>,<sp2>,...
451	       ipmi_si.regsizes=<size1>,<size2>,...
452	       ipmi_si.regshifts=<shift1>,<shift2>,...
453	       ipmi_si.slave_addrs=<addr1>,<addr2>,...
454	       ipmi_si.force_kipmid=<enable1>,<enable2>,...
455	       ipmi_si.kipmid_max_busy_us=<ustime1>,<ustime2>,...
456	
457	It works the same as the module parameters of the same names.
458	
459	If your IPMI interface does not support interrupts and is a KCS or
460	SMIC interface, the IPMI driver will start a kernel thread for the
461	interface to help speed things up.  This is a low-priority kernel
462	thread that constantly polls the IPMI driver while an IPMI operation
463	is in progress.  The force_kipmid module parameter will all the user to
464	force this thread on or off.  If you force it off and don't have
465	interrupts, the driver will run VERY slowly.  Don't blame me,
466	these interfaces suck.
467	
468	Unfortunately, this thread can use a lot of CPU depending on the
469	interface's performance.  This can waste a lot of CPU and cause
470	various issues with detecting idle CPU and using extra power.  To
471	avoid this, the kipmid_max_busy_us sets the maximum amount of time, in
472	microseconds, that kipmid will spin before sleeping for a tick.  This
473	value sets a balance between performance and CPU waste and needs to be
474	tuned to your needs.  Maybe, someday, auto-tuning will be added, but
475	that's not a simple thing and even the auto-tuning would need to be
476	tuned to the user's desired performance.
477	
478	The driver supports a hot add and remove of interfaces.  This way,
479	interfaces can be added or removed after the kernel is up and running.
480	This is done using /sys/modules/ipmi_si/parameters/hotmod, which is a
481	write-only parameter.  You write a string to this interface.  The string
482	has the format::
483	
484	   <op1>[:op2[:op3...]]
485	
486	The "op"s are::
487	
488	   add|remove,kcs|bt|smic,mem|i/o,<address>[,<opt1>[,<opt2>[,...]]]
489	
490	You can specify more than one interface on the line.  The "opt"s are::
491	
492	   rsp=<regspacing>
493	   rsi=<regsize>
494	   rsh=<regshift>
495	   irq=<irq>
496	   ipmb=<ipmb slave addr>
497	
498	and these have the same meanings as discussed above.  Note that you
499	can also use this on the kernel command line for a more compact format
500	for specifying an interface.  Note that when removing an interface,
501	only the first three parameters (si type, address type, and address)
502	are used for the comparison.  Any options are ignored for removing.
503	
504	The SMBus Driver (SSIF)
505	-----------------------
506	
507	The SMBus driver allows up to 4 SMBus devices to be configured in the
508	system.  By default, the driver will only register with something it
509	finds in DMI or ACPI tables.  You can change this
510	at module load time (for a module) with::
511	
512	  modprobe ipmi_ssif.o
513		addr=<i2caddr1>[,<i2caddr2>[,...]]
514		adapter=<adapter1>[,<adapter2>[...]]
515		dbg=<flags1>,<flags2>...
516		slave_addrs=<addr1>,<addr2>,...
517		tryacpi=[0|1] trydmi=[0|1]
518		[dbg_probe=1]
519	
520	The addresses are normal I2C addresses.  The adapter is the string
521	name of the adapter, as shown in /sys/class/i2c-adapter/i2c-<n>/name.
522	It is *NOT* i2c-<n> itself.  Also, the comparison is done ignoring
523	spaces, so if the name is "This is an I2C chip" you can say
524	adapter_name=ThisisanI2cchip.  This is because it's hard to pass in
525	spaces in kernel parameters.
526	
527	The debug flags are bit flags for each BMC found, they are:
528	IPMI messages: 1, driver state: 2, timing: 4, I2C probe: 8
529	
530	The tryxxx parameters can be used to disable detecting interfaces
531	from various sources.
532	
533	Setting dbg_probe to 1 will enable debugging of the probing and
534	detection process for BMCs on the SMBusses.
535	
536	The slave_addrs specifies the IPMI address of the local BMC.  This is
537	usually 0x20 and the driver defaults to that, but in case it's not, it
538	can be specified when the driver starts up.
539	
540	Discovering the IPMI compliant BMC on the SMBus can cause devices on
541	the I2C bus to fail. The SMBus driver writes a "Get Device ID" IPMI
542	message as a block write to the I2C bus and waits for a response.
543	This action can be detrimental to some I2C devices. It is highly
544	recommended that the known I2C address be given to the SMBus driver in
545	the smb_addr parameter unless you have DMI or ACPI data to tell the
546	driver what to use.
547	
548	When compiled into the kernel, the addresses can be specified on the
549	kernel command line as::
550	
551	  ipmb_ssif.addr=<i2caddr1>[,<i2caddr2>[...]]
552		ipmi_ssif.adapter=<adapter1>[,<adapter2>[...]]
553		ipmi_ssif.dbg=<flags1>[,<flags2>[...]]
554		ipmi_ssif.dbg_probe=1
555		ipmi_ssif.slave_addrs=<addr1>[,<addr2>[...]]
556		ipmi_ssif.tryacpi=[0|1] ipmi_ssif.trydmi=[0|1]
557	
558	These are the same options as on the module command line.
559	
560	The I2C driver does not support non-blocking access or polling, so
561	this driver cannod to IPMI panic events, extend the watchdog at panic
562	time, or other panic-related IPMI functions without special kernel
563	patches and driver modifications.  You can get those at the openipmi
564	web page.
565	
566	The driver supports a hot add and remove of interfaces through the I2C
567	sysfs interface.
568	
569	Other Pieces
570	------------
571	
572	Get the detailed info related with the IPMI device
573	--------------------------------------------------
574	
575	Some users need more detailed information about a device, like where
576	the address came from or the raw base device for the IPMI interface.
577	You can use the IPMI smi_watcher to catch the IPMI interfaces as they
578	come or go, and to grab the information, you can use the function
579	ipmi_get_smi_info(), which returns the following structure::
580	
581	  struct ipmi_smi_info {
582		enum ipmi_addr_src addr_src;
583		struct device *dev;
584		union {
585			struct {
586				void *acpi_handle;
587			} acpi_info;
588		} addr_info;
589	  };
590	
591	Currently special info for only for SI_ACPI address sources is
592	returned.  Others may be added as necessary.
593	
594	Note that the dev pointer is included in the above structure, and
595	assuming ipmi_smi_get_info returns success, you must call put_device
596	on the dev pointer.
597	
598	
599	Watchdog
600	--------
601	
602	A watchdog timer is provided that implements the Linux-standard
603	watchdog timer interface.  It has three module parameters that can be
604	used to control it::
605	
606	  modprobe ipmi_watchdog timeout=<t> pretimeout=<t> action=<action type>
607	      preaction=<preaction type> preop=<preop type> start_now=x
608	      nowayout=x ifnum_to_use=n panic_wdt_timeout=<t>
609	
610	ifnum_to_use specifies which interface the watchdog timer should use.
611	The default is -1, which means to pick the first one registered.
612	
613	The timeout is the number of seconds to the action, and the pretimeout
614	is the amount of seconds before the reset that the pre-timeout panic will
615	occur (if pretimeout is zero, then pretimeout will not be enabled).  Note
616	that the pretimeout is the time before the final timeout.  So if the
617	timeout is 50 seconds and the pretimeout is 10 seconds, then the pretimeout
618	will occur in 40 second (10 seconds before the timeout). The panic_wdt_timeout
619	is the value of timeout which is set on kernel panic, in order to let actions
620	such as kdump to occur during panic.
621	
622	The action may be "reset", "power_cycle", or "power_off", and
623	specifies what to do when the timer times out, and defaults to
624	"reset".
625	
626	The preaction may be "pre_smi" for an indication through the SMI
627	interface, "pre_int" for an indication through the SMI with an
628	interrupts, and "pre_nmi" for a NMI on a preaction.  This is how
629	the driver is informed of the pretimeout.
630	
631	The preop may be set to "preop_none" for no operation on a pretimeout,
632	"preop_panic" to set the preoperation to panic, or "preop_give_data"
633	to provide data to read from the watchdog device when the pretimeout
634	occurs.  A "pre_nmi" setting CANNOT be used with "preop_give_data"
635	because you can't do data operations from an NMI.
636	
637	When preop is set to "preop_give_data", one byte comes ready to read
638	on the device when the pretimeout occurs.  Select and fasync work on
639	the device, as well.
640	
641	If start_now is set to 1, the watchdog timer will start running as
642	soon as the driver is loaded.
643	
644	If nowayout is set to 1, the watchdog timer will not stop when the
645	watchdog device is closed.  The default value of nowayout is true
646	if the CONFIG_WATCHDOG_NOWAYOUT option is enabled, or false if not.
647	
648	When compiled into the kernel, the kernel command line is available
649	for configuring the watchdog::
650	
651	  ipmi_watchdog.timeout=<t> ipmi_watchdog.pretimeout=<t>
652		ipmi_watchdog.action=<action type>
653		ipmi_watchdog.preaction=<preaction type>
654		ipmi_watchdog.preop=<preop type>
655		ipmi_watchdog.start_now=x
656		ipmi_watchdog.nowayout=x
657		ipmi_watchdog.panic_wdt_timeout=<t>
658	
659	The options are the same as the module parameter options.
660	
661	The watchdog will panic and start a 120 second reset timeout if it
662	gets a pre-action.  During a panic or a reboot, the watchdog will
663	start a 120 timer if it is running to make sure the reboot occurs.
664	
665	Note that if you use the NMI preaction for the watchdog, you MUST NOT
666	use the nmi watchdog.  There is no reasonable way to tell if an NMI
667	comes from the IPMI controller, so it must assume that if it gets an
668	otherwise unhandled NMI, it must be from IPMI and it will panic
669	immediately.
670	
671	Once you open the watchdog timer, you must write a 'V' character to the
672	device to close it, or the timer will not stop.  This is a new semantic
673	for the driver, but makes it consistent with the rest of the watchdog
674	drivers in Linux.
675	
676	
677	Panic Timeouts
678	--------------
679	
680	The OpenIPMI driver supports the ability to put semi-custom and custom
681	events in the system event log if a panic occurs.  if you enable the
682	'Generate a panic event to all BMCs on a panic' option, you will get
683	one event on a panic in a standard IPMI event format.  If you enable
684	the 'Generate OEM events containing the panic string' option, you will
685	also get a bunch of OEM events holding the panic string.
686	
687	
688	The field settings of the events are:
689	
690	* Generator ID: 0x21 (kernel)
691	* EvM Rev: 0x03 (this event is formatting in IPMI 1.0 format)
692	* Sensor Type: 0x20 (OS critical stop sensor)
693	* Sensor #: The first byte of the panic string (0 if no panic string)
694	* Event Dir | Event Type: 0x6f (Assertion, sensor-specific event info)
695	* Event Data 1: 0xa1 (Runtime stop in OEM bytes 2 and 3)
696	* Event data 2: second byte of panic string
697	* Event data 3: third byte of panic string
698	
699	See the IPMI spec for the details of the event layout.  This event is
700	always sent to the local management controller.  It will handle routing
701	the message to the right place
702	
703	Other OEM events have the following format:
704	
705	* Record ID (bytes 0-1): Set by the SEL.
706	* Record type (byte 2): 0xf0 (OEM non-timestamped)
707	* byte 3: The slave address of the card saving the panic
708	* byte 4: A sequence number (starting at zero)
709	  The rest of the bytes (11 bytes) are the panic string.  If the panic string
710	  is longer than 11 bytes, multiple messages will be sent with increasing
711	  sequence numbers.
712	
713	Because you cannot send OEM events using the standard interface, this
714	function will attempt to find an SEL and add the events there.  It
715	will first query the capabilities of the local management controller.
716	If it has an SEL, then they will be stored in the SEL of the local
717	management controller.  If not, and the local management controller is
718	an event generator, the event receiver from the local management
719	controller will be queried and the events sent to the SEL on that
720	device.  Otherwise, the events go nowhere since there is nowhere to
721	send them.
722	
723	
724	Poweroff
725	--------
726	
727	If the poweroff capability is selected, the IPMI driver will install
728	a shutdown function into the standard poweroff function pointer.  This
729	is in the ipmi_poweroff module.  When the system requests a powerdown,
730	it will send the proper IPMI commands to do this.  This is supported on
731	several platforms.
732	
733	There is a module parameter named "poweroff_powercycle" that may
734	either be zero (do a power down) or non-zero (do a power cycle, power
735	the system off, then power it on in a few seconds).  Setting
736	ipmi_poweroff.poweroff_control=x will do the same thing on the kernel
737	command line.  The parameter is also available via the proc filesystem
738	in /proc/sys/dev/ipmi/poweroff_powercycle.  Note that if the system
739	does not support power cycling, it will always do the power off.
740	
741	The "ifnum_to_use" parameter specifies which interface the poweroff
742	code should use.  The default is -1, which means to pick the first one
743	registered.
744	
745	Note that if you have ACPI enabled, the system will prefer using ACPI to
746	power off.
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