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Based on kernel version 3.19. Page generated on 2015-02-13 21:21 EST.

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