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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
154 IPMI_BMC_CHANNEL.
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
278 the IPMICTL_RECEIVE_MSG_TRUNC ioctl.
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.