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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 EST.

2	                          The Linux IPMI Driver
3				  ---------------------
4				      Corey Minyard
5				  <minyard@mvista.com>
6				    <minyard@acm.org>
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.
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.
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!
25	Configuration
26	-------------
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.
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.
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.
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.
47	You should generally enable ACPI on your system, as systems with IPMI
48	can have ACPI tables describing them.
50	If you have a standard interface and the board manufacturer has done
51	their job correctly, the IPMI controller should be automatically
52	detected (via ACPI or SMBIOS tables) and should just work.  Sadly,
53	many boards do not have this information.  The driver attempts
54	standard defaults, but they may not work.  If you fall into this
55	situation, you need to read the section below named 'The SI Driver'.
57	IPMI defines a standard watchdog timer.  You can enable this with the
58	'IPMI Watchdog Timer' config option.  If you compile the driver into
59	the kernel, then via a kernel command-line option you can have the
60	watchdog timer start as soon as it initializes.  It also have a lot
61	of other options, see the 'Watchdog' section below for more details.
62	Note that you can also have the watchdog continue to run if it is
63	closed (by default it is disabled on close).  Go into the 'Watchdog
64	Cards' menu, enable 'Watchdog Timer Support', and enable the option
65	'Disable watchdog shutdown on close'.
67	IPMI systems can often be powered off using IPMI commands.  Select
68	'IPMI Poweroff' to do this.  The driver will auto-detect if the system
69	can be powered off by IPMI.  It is safe to enable this even if your
70	system doesn't support this option.  This works on ATCA systems, the
71	Radisys CPI1 card, and any IPMI system that supports standard chassis
72	management commands.
74	If you want the driver to put an event into the event log on a panic,
75	enable the 'Generate a panic event to all BMCs on a panic' option.  If
76	you want the whole panic string put into the event log using OEM
77	events, enable the 'Generate OEM events containing the panic string'
78	option.
80	Basic Design
81	------------
83	The Linux IPMI driver is designed to be very modular and flexible, you
84	only need to take the pieces you need and you can use it in many
85	different ways.  Because of that, it's broken into many chunks of
86	code.  These chunks (by module name) are:
88	ipmi_msghandler - This is the central piece of software for the IPMI
89	system.  It handles all messages, message timing, and responses.  The
90	IPMI users tie into this, and the IPMI physical interfaces (called
91	System Management Interfaces, or SMIs) also tie in here.  This
92	provides the kernelland interface for IPMI, but does not provide an
93	interface for use by application processes.
95	ipmi_devintf - This provides a userland IOCTL interface for the IPMI
96	driver, each open file for this device ties in to the message handler
97	as an IPMI user.
99	ipmi_si - A driver for various system interfaces.  This supports KCS,
100	SMIC, and BT interfaces.
102	ipmi_watchdog - IPMI requires systems to have a very capable watchdog
103	timer.  This driver implements the standard Linux watchdog timer
104	interface on top of the IPMI message handler.
106	ipmi_poweroff - Some systems support the ability to be turned off via
107	IPMI commands.
109	These are all individually selectable via configuration options.
111	Note that the KCS-only interface has been removed.  The af_ipmi driver
112	is no longer supported and has been removed because it was impossible
113	to do 32 bit emulation on 64-bit kernels with it.
115	Much documentation for the interface is in the include files.  The
116	IPMI include files are:
118	net/af_ipmi.h - Contains the socket interface.
120	linux/ipmi.h - Contains the user interface and IOCTL interface for IPMI.
122	linux/ipmi_smi.h - Contains the interface for system management interfaces
123	(things that interface to IPMI controllers) to use.
125	linux/ipmi_msgdefs.h - General definitions for base IPMI messaging.
128	Addressing
129	----------
131	The IPMI addressing works much like IP addresses, you have an overlay
132	to handle the different address types.  The overlay is:
134	  struct ipmi_addr
135	  {
136		int   addr_type;
137		short channel;
138		char  data[IPMI_MAX_ADDR_SIZE];
139	  };
141	The addr_type determines what the address really is.  The driver
142	currently understands two different types of addresses.
144	"System Interface" addresses are defined as:
146	  struct ipmi_system_interface_addr
147	  {
148		int   addr_type;
149		short channel;
150	  };
152	and the type is IPMI_SYSTEM_INTERFACE_ADDR_TYPE.  This is used for talking
153	straight to the BMC on the current card.  The channel must be
156	Messages that are destined to go out on the IPMB bus use the
157	IPMI_IPMB_ADDR_TYPE address type.  The format is
159	  struct ipmi_ipmb_addr
160	  {
161		int           addr_type;
162		short         channel;
163		unsigned char slave_addr;
164		unsigned char lun;
165	  };
167	The "channel" here is generally zero, but some devices support more
168	than one channel, it corresponds to the channel as defined in the IPMI
169	spec.
172	Messages
173	--------
175	Messages are defined as:
177	struct ipmi_msg
178	{
179		unsigned char netfn;
180		unsigned char lun;
181		unsigned char cmd;
182		unsigned char *data;
183		int           data_len;
184	};
186	The driver takes care of adding/stripping the header information.  The
187	data portion is just the data to be send (do NOT put addressing info
188	here) or the response.  Note that the completion code of a response is
189	the first item in "data", it is not stripped out because that is how
190	all the messages are defined in the spec (and thus makes counting the
191	offsets a little easier :-).
193	When using the IOCTL interface from userland, you must provide a block
194	of data for "data", fill it, and set data_len to the length of the
195	block of data, even when receiving messages.  Otherwise the driver
196	will have no place to put the message.
198	Messages coming up from the message handler in kernelland will come in
199	as:
201	  struct ipmi_recv_msg
202	  {
203		struct list_head link;
205		/* The type of message as defined in the "Receive Types"
206	           defines above. */
207		int         recv_type;
209		ipmi_user_t      *user;
210		struct ipmi_addr addr;
211		long             msgid;
212		struct ipmi_msg  msg;
214		/* Call this when done with the message.  It will presumably free
215		   the message and do any other necessary cleanup. */
216		void (*done)(struct ipmi_recv_msg *msg);
218		/* Place-holder for the data, don't make any assumptions about
219		   the size or existence of this, since it may change. */
220		unsigned char   msg_data[IPMI_MAX_MSG_LENGTH];
221	  };
223	You should look at the receive type and handle the message
224	appropriately.
227	The Upper Layer Interface (Message Handler)
228	-------------------------------------------
230	The upper layer of the interface provides the users with a consistent
231	view of the IPMI interfaces.  It allows multiple SMI interfaces to be
232	addressed (because some boards actually have multiple BMCs on them)
233	and the user should not have to care what type of SMI is below them.
236	Creating the User
238	To user the message handler, you must first create a user using
239	ipmi_create_user.  The interface number specifies which SMI you want
240	to connect to, and you must supply callback functions to be called
241	when data comes in.  The callback function can run at interrupt level,
242	so be careful using the callbacks.  This also allows to you pass in a
243	piece of data, the handler_data, that will be passed back to you on
244	all calls.
246	Once you are done, call ipmi_destroy_user() to get rid of the user.
248	From userland, opening the device automatically creates a user, and
249	closing the device automatically destroys the user.
252	Messaging
254	To send a message from kernel-land, the ipmi_request() call does
255	pretty much all message handling.  Most of the parameter are
256	self-explanatory.  However, it takes a "msgid" parameter.  This is NOT
257	the sequence number of messages.  It is simply a long value that is
258	passed back when the response for the message is returned.  You may
259	use it for anything you like.
261	Responses come back in the function pointed to by the ipmi_recv_hndl
262	field of the "handler" that you passed in to ipmi_create_user().
263	Remember again, these may be running at interrupt level.  Remember to
264	look at the receive type, too.
266	From userland, you fill out an ipmi_req_t structure and use the
267	IPMICTL_SEND_COMMAND ioctl.  For incoming stuff, you can use select()
268	or poll() to wait for messages to come in.  However, you cannot use
269	read() to get them, you must call the IPMICTL_RECEIVE_MSG with the
270	ipmi_recv_t structure to actually get the message.  Remember that you
271	must supply a pointer to a block of data in the msg.data field, and
272	you must fill in the msg.data_len field with the size of the data.
273	This gives the receiver a place to actually put the message.
275	If the message cannot fit into the data you provide, you will get an
276	EMSGSIZE error and the driver will leave the data in the receive
277	queue.  If you want to get it and have it truncate the message, us
280	When you send a command (which is defined by the lowest-order bit of
281	the netfn per the IPMI spec) on the IPMB bus, the driver will
282	automatically assign the sequence number to the command and save the
283	command.  If the response is not receive in the IPMI-specified 5
284	seconds, it will generate a response automatically saying the command
285	timed out.  If an unsolicited response comes in (if it was after 5
286	seconds, for instance), that response will be ignored.
288	In kernelland, after you receive a message and are done with it, you
289	MUST call ipmi_free_recv_msg() on it, or you will leak messages.  Note
290	that you should NEVER mess with the "done" field of a message, that is
291	required to properly clean up the message.
293	Note that when sending, there is an ipmi_request_supply_msgs() call
294	that lets you supply the smi and receive message.  This is useful for
295	pieces of code that need to work even if the system is out of buffers
296	(the watchdog timer uses this, for instance).  You supply your own
297	buffer and own free routines.  This is not recommended for normal use,
298	though, since it is tricky to manage your own buffers.
301	Events and Incoming Commands
303	The driver takes care of polling for IPMI events and receiving
304	commands (commands are messages that are not responses, they are
305	commands that other things on the IPMB bus have sent you).  To receive
306	these, you must register for them, they will not automatically be sent
307	to you.
309	To receive events, you must call ipmi_set_gets_events() and set the
310	"val" to non-zero.  Any events that have been received by the driver
311	since startup will immediately be delivered to the first user that
312	registers for events.  After that, if multiple users are registered
313	for events, they will all receive all events that come in.
315	For receiving commands, you have to individually register commands you
316	want to receive.  Call ipmi_register_for_cmd() and supply the netfn
317	and command name for each command you want to receive.  You also
318	specify a bitmask of the channels you want to receive the command from
319	(or use IPMI_CHAN_ALL for all channels if you don't care).  Only one
320	user may be registered for each netfn/cmd/channel, but different users
321	may register for different commands, or the same command if the
322	channel bitmasks do not overlap.
324	From userland, equivalent IOCTLs are provided to do these functions.
327	The Lower Layer (SMI) Interface
328	-------------------------------
330	As mentioned before, multiple SMI interfaces may be registered to the
331	message handler, each of these is assigned an interface number when
332	they register with the message handler.  They are generally assigned
333	in the order they register, although if an SMI unregisters and then
334	another one registers, all bets are off.
336	The ipmi_smi.h defines the interface for management interfaces, see
337	that for more details.
340	The SI Driver
341	-------------
343	The SI driver allows up to 4 KCS or SMIC interfaces to be configured
344	in the system.  By default, scan the ACPI tables for interfaces, and
345	if it doesn't find any the driver will attempt to register one KCS
346	interface at the spec-specified I/O port 0xca2 without interrupts.
347	You can change this at module load time (for a module) with:
349	  modprobe ipmi_si.o type=<type1>,<type2>....
350	       ports=<port1>,<port2>... addrs=<addr1>,<addr2>...
351	       irqs=<irq1>,<irq2>...
352	       regspacings=<sp1>,<sp2>,... regsizes=<size1>,<size2>,...
353	       regshifts=<shift1>,<shift2>,...
354	       slave_addrs=<addr1>,<addr2>,...
355	       force_kipmid=<enable1>,<enable2>,...
356	       kipmid_max_busy_us=<ustime1>,<ustime2>,...
357	       unload_when_empty=[0|1]
358	       trydefaults=[0|1] trydmi=[0|1] tryacpi=[0|1]
359	       tryplatform=[0|1] trypci=[0|1]
361	Each of these except try... items is a list, the first item for the
362	first interface, second item for the second interface, etc.
364	The si_type may be either "kcs", "smic", or "bt".  If you leave it blank, it
365	defaults to "kcs".
367	If you specify addrs as non-zero for an interface, the driver will
368	use the memory address given as the address of the device.  This
369	overrides si_ports.
371	If you specify ports as non-zero for an interface, the driver will
372	use the I/O port given as the device address.
374	If you specify irqs as non-zero for an interface, the driver will
375	attempt to use the given interrupt for the device.
377	trydefaults sets whether the standard IPMI interface at 0xca2 and
378	any interfaces specified by ACPE are tried.  By default, the driver
379	tries it, set this value to zero to turn this off.
381	The other try... items disable discovery by their corresponding
382	names.  These are all enabled by default, set them to zero to disable
383	them.  The tryplatform disables openfirmware.
385	The next three parameters have to do with register layout.  The
386	registers used by the interfaces may not appear at successive
387	locations and they may not be in 8-bit registers.  These parameters
388	allow the layout of the data in the registers to be more precisely
389	specified.
391	The regspacings parameter give the number of bytes between successive
392	register start addresses.  For instance, if the regspacing is set to 4
393	and the start address is 0xca2, then the address for the second
394	register would be 0xca6.  This defaults to 1.
396	The regsizes parameter gives the size of a register, in bytes.  The
397	data used by IPMI is 8-bits wide, but it may be inside a larger
398	register.  This parameter allows the read and write type to specified.
399	It may be 1, 2, 4, or 8.  The default is 1.
401	Since the register size may be larger than 32 bits, the IPMI data may not
402	be in the lower 8 bits.  The regshifts parameter give the amount to shift
403	the data to get to the actual IPMI data.
405	The slave_addrs specifies the IPMI address of the local BMC.  This is
406	usually 0x20 and the driver defaults to that, but in case it's not, it
407	can be specified when the driver starts up.
409	The force_ipmid parameter forcefully enables (if set to 1) or disables
410	(if set to 0) the kernel IPMI daemon.  Normally this is auto-detected
411	by the driver, but systems with broken interrupts might need an enable,
412	or users that don't want the daemon (don't need the performance, don't
413	want the CPU hit) can disable it.
415	If unload_when_empty is set to 1, the driver will be unloaded if it
416	doesn't find any interfaces or all the interfaces fail to work.  The
417	default is one.  Setting to 0 is useful with the hotmod, but is
418	obviously only useful for modules.
420	When compiled into the kernel, the parameters can be specified on the
421	kernel command line as:
423	  ipmi_si.type=<type1>,<type2>...
424	       ipmi_si.ports=<port1>,<port2>... ipmi_si.addrs=<addr1>,<addr2>...
425	       ipmi_si.irqs=<irq1>,<irq2>... ipmi_si.trydefaults=[0|1]
426	       ipmi_si.regspacings=<sp1>,<sp2>,...
427	       ipmi_si.regsizes=<size1>,<size2>,...
428	       ipmi_si.regshifts=<shift1>,<shift2>,...
429	       ipmi_si.slave_addrs=<addr1>,<addr2>,...
430	       ipmi_si.force_kipmid=<enable1>,<enable2>,...
431	       ipmi_si.kipmid_max_busy_us=<ustime1>,<ustime2>,...
433	It works the same as the module parameters of the same names.
435	By default, the driver will attempt to detect any device specified by
436	ACPI, and if none of those then a KCS device at the spec-specified
437	0xca2.  If you want to turn this off, set the "trydefaults" option to
438	false.
440	If your IPMI interface does not support interrupts and is a KCS or
441	SMIC interface, the IPMI driver will start a kernel thread for the
442	interface to help speed things up.  This is a low-priority kernel
443	thread that constantly polls the IPMI driver while an IPMI operation
444	is in progress.  The force_kipmid module parameter will all the user to
445	force this thread on or off.  If you force it off and don't have
446	interrupts, the driver will run VERY slowly.  Don't blame me,
447	these interfaces suck.
449	Unfortunately, this thread can use a lot of CPU depending on the
450	interface's performance.  This can waste a lot of CPU and cause
451	various issues with detecting idle CPU and using extra power.  To
452	avoid this, the kipmid_max_busy_us sets the maximum amount of time, in
453	microseconds, that kipmid will spin before sleeping for a tick.  This
454	value sets a balance between performance and CPU waste and needs to be
455	tuned to your needs.  Maybe, someday, auto-tuning will be added, but
456	that's not a simple thing and even the auto-tuning would need to be
457	tuned to the user's desired performance.
459	The driver supports a hot add and remove of interfaces.  This way,
460	interfaces can be added or removed after the kernel is up and running.
461	This is done using /sys/modules/ipmi_si/parameters/hotmod, which is a
462	write-only parameter.  You write a string to this interface.  The string
463	has the format:
464	   <op1>[:op2[:op3...]]
465	The "op"s are:
466	   add|remove,kcs|bt|smic,mem|i/o,<address>[,<opt1>[,<opt2>[,...]]]
467	You can specify more than one interface on the line.  The "opt"s are:
468	   rsp=<regspacing>
469	   rsi=<regsize>
470	   rsh=<regshift>
471	   irq=<irq>
472	   ipmb=<ipmb slave addr>
473	and these have the same meanings as discussed above.  Note that you
474	can also use this on the kernel command line for a more compact format
475	for specifying an interface.  Note that when removing an interface,
476	only the first three parameters (si type, address type, and address)
477	are used for the comparison.  Any options are ignored for removing.
480	Other Pieces
481	------------
483	Get the detailed info related with the IPMI device
484	--------------------------------------------------
486	Some users need more detailed information about a device, like where
487	the address came from or the raw base device for the IPMI interface.
488	You can use the IPMI smi_watcher to catch the IPMI interfaces as they
489	come or go, and to grab the information, you can use the function
490	ipmi_get_smi_info(), which returns the following structure:
492	struct ipmi_smi_info {
493		enum ipmi_addr_src addr_src;
494		struct device *dev;
495		union {
496			struct {
497				void *acpi_handle;
498			} acpi_info;
499		} addr_info;
500	};
502	Currently special info for only for SI_ACPI address sources is
503	returned.  Others may be added as necessary.
505	Note that the dev pointer is included in the above structure, and
506	assuming ipmi_smi_get_info returns success, you must call put_device
507	on the dev pointer.
510	Watchdog
511	--------
513	A watchdog timer is provided that implements the Linux-standard
514	watchdog timer interface.  It has three module parameters that can be
515	used to control it:
517	  modprobe ipmi_watchdog timeout=<t> pretimeout=<t> action=<action type>
518	      preaction=<preaction type> preop=<preop type> start_now=x
519	      nowayout=x ifnum_to_use=n
521	ifnum_to_use specifies which interface the watchdog timer should use.
522	The default is -1, which means to pick the first one registered.
524	The timeout is the number of seconds to the action, and the pretimeout
525	is the amount of seconds before the reset that the pre-timeout panic will
526	occur (if pretimeout is zero, then pretimeout will not be enabled).  Note
527	that the pretimeout is the time before the final timeout.  So if the
528	timeout is 50 seconds and the pretimeout is 10 seconds, then the pretimeout
529	will occur in 40 second (10 seconds before the timeout).
531	The action may be "reset", "power_cycle", or "power_off", and
532	specifies what to do when the timer times out, and defaults to
533	"reset".
535	The preaction may be "pre_smi" for an indication through the SMI
536	interface, "pre_int" for an indication through the SMI with an
537	interrupts, and "pre_nmi" for a NMI on a preaction.  This is how
538	the driver is informed of the pretimeout.
540	The preop may be set to "preop_none" for no operation on a pretimeout,
541	"preop_panic" to set the preoperation to panic, or "preop_give_data"
542	to provide data to read from the watchdog device when the pretimeout
543	occurs.  A "pre_nmi" setting CANNOT be used with "preop_give_data"
544	because you can't do data operations from an NMI.
546	When preop is set to "preop_give_data", one byte comes ready to read
547	on the device when the pretimeout occurs.  Select and fasync work on
548	the device, as well.
550	If start_now is set to 1, the watchdog timer will start running as
551	soon as the driver is loaded.
553	If nowayout is set to 1, the watchdog timer will not stop when the
554	watchdog device is closed.  The default value of nowayout is true
555	if the CONFIG_WATCHDOG_NOWAYOUT option is enabled, or false if not.
557	When compiled into the kernel, the kernel command line is available
558	for configuring the watchdog:
560	  ipmi_watchdog.timeout=<t> ipmi_watchdog.pretimeout=<t>
561		ipmi_watchdog.action=<action type>
562		ipmi_watchdog.preaction=<preaction type>
563		ipmi_watchdog.preop=<preop type>
564		ipmi_watchdog.start_now=x
565		ipmi_watchdog.nowayout=x
567	The options are the same as the module parameter options.
569	The watchdog will panic and start a 120 second reset timeout if it
570	gets a pre-action.  During a panic or a reboot, the watchdog will
571	start a 120 timer if it is running to make sure the reboot occurs.
573	Note that if you use the NMI preaction for the watchdog, you MUST NOT
574	use the nmi watchdog.  There is no reasonable way to tell if an NMI
575	comes from the IPMI controller, so it must assume that if it gets an
576	otherwise unhandled NMI, it must be from IPMI and it will panic
577	immediately.
579	Once you open the watchdog timer, you must write a 'V' character to the
580	device to close it, or the timer will not stop.  This is a new semantic
581	for the driver, but makes it consistent with the rest of the watchdog
582	drivers in Linux.
585	Panic Timeouts
586	--------------
588	The OpenIPMI driver supports the ability to put semi-custom and custom
589	events in the system event log if a panic occurs.  if you enable the
590	'Generate a panic event to all BMCs on a panic' option, you will get
591	one event on a panic in a standard IPMI event format.  If you enable
592	the 'Generate OEM events containing the panic string' option, you will
593	also get a bunch of OEM events holding the panic string.
596	The field settings of the events are:
597	* Generator ID: 0x21 (kernel)
598	* EvM Rev: 0x03 (this event is formatting in IPMI 1.0 format)
599	* Sensor Type: 0x20 (OS critical stop sensor)
600	* Sensor #: The first byte of the panic string (0 if no panic string)
601	* Event Dir | Event Type: 0x6f (Assertion, sensor-specific event info)
602	* Event Data 1: 0xa1 (Runtime stop in OEM bytes 2 and 3)
603	* Event data 2: second byte of panic string
604	* Event data 3: third byte of panic string
605	See the IPMI spec for the details of the event layout.  This event is
606	always sent to the local management controller.  It will handle routing
607	the message to the right place
609	Other OEM events have the following format:
610	Record ID (bytes 0-1): Set by the SEL.
611	Record type (byte 2): 0xf0 (OEM non-timestamped)
612	byte 3: The slave address of the card saving the panic
613	byte 4: A sequence number (starting at zero)
614	The rest of the bytes (11 bytes) are the panic string.  If the panic string
615	is longer than 11 bytes, multiple messages will be sent with increasing
616	sequence numbers.
618	Because you cannot send OEM events using the standard interface, this
619	function will attempt to find an SEL and add the events there.  It
620	will first query the capabilities of the local management controller.
621	If it has an SEL, then they will be stored in the SEL of the local
622	management controller.  If not, and the local management controller is
623	an event generator, the event receiver from the local management
624	controller will be queried and the events sent to the SEL on that
625	device.  Otherwise, the events go nowhere since there is nowhere to
626	send them.
629	Poweroff
630	--------
632	If the poweroff capability is selected, the IPMI driver will install
633	a shutdown function into the standard poweroff function pointer.  This
634	is in the ipmi_poweroff module.  When the system requests a powerdown,
635	it will send the proper IPMI commands to do this.  This is supported on
636	several platforms.
638	There is a module parameter named "poweroff_powercycle" that may
639	either be zero (do a power down) or non-zero (do a power cycle, power
640	the system off, then power it on in a few seconds).  Setting
641	ipmi_poweroff.poweroff_control=x will do the same thing on the kernel
642	command line.  The parameter is also available via the proc filesystem
643	in /proc/sys/dev/ipmi/poweroff_powercycle.  Note that if the system
644	does not support power cycling, it will always do the power off.
646	The "ifnum_to_use" parameter specifies which interface the poweroff
647	code should use.  The default is -1, which means to pick the first one
648	registered.
650	Note that if you have ACPI enabled, the system will prefer using ACPI to
651	power off.
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