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  2                           The Linux IPMI Driver
  3                           ---------------------
  4                               Corey Minyard
  5                           <>
  6                             <>
  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  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.  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.
 53 You should generally enable ACPI on your system, as systems with IPMI
 54 can have ACPI tables describing them.
 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.
 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'.
 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.
 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.
 87 Basic Design
 88 ------------
 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:
 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.
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.
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.
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.
114 ipmi_powernv - A driver for access BMCs on POWERNV systems.
116 ipmi_watchdog - IPMI requires systems to have a very capable watchdog
117 timer.  This driver implements the standard Linux watchdog timer
118 interface on top of the IPMI message handler.
120 ipmi_poweroff - Some systems support the ability to be turned off via
121 IPMI commands.
123 bt-bmc - This is not part of the main driver, but instead a driver for
124 accessing a BMC-side interface of a BT interface.  It is used on BMCs
125 running Linux to provide an interface to the host.
127 These are all individually selectable via configuration options.
129 Much documentation for the interface is in the include files.  The
130 IPMI include files are:
132 linux/ipmi.h - Contains the user interface and IOCTL interface for IPMI.
134 linux/ipmi_smi.h - Contains the interface for system management interfaces
135 (things that interface to IPMI controllers) to use.
137 linux/ipmi_msgdefs.h - General definitions for base IPMI messaging.
140 Addressing
141 ----------
143 The IPMI addressing works much like IP addresses, you have an overlay
144 to handle the different address types.  The overlay is:
146   struct ipmi_addr
147   {
148         int   addr_type;
149         short channel;
150         char  data[IPMI_MAX_ADDR_SIZE];
151   };
153 The addr_type determines what the address really is.  The driver
154 currently understands two different types of addresses.
156 "System Interface" addresses are defined as:
158   struct ipmi_system_interface_addr
159   {
160         int   addr_type;
161         short channel;
162   };
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
168 Messages that are destined to go out on the IPMB bus use the
169 IPMI_IPMB_ADDR_TYPE address type.  The format is
171   struct ipmi_ipmb_addr
172   {
173         int           addr_type;
174         short         channel;
175         unsigned char slave_addr;
176         unsigned char lun;
177   };
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.
184 Messages
185 --------
187 Messages are defined as:
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 };
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 :-).
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.
210 Messages coming up from the message handler in kernelland will come in
211 as:
213   struct ipmi_recv_msg
214   {
215         struct list_head link;
217         /* The type of message as defined in the "Receive Types"
218            defines above. */
219         int         recv_type;
221         ipmi_user_t      *user;
222         struct ipmi_addr addr;
223         long             msgid;
224         struct ipmi_msg  msg;
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);
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   };
235 You should look at the receive type and handle the message
236 appropriately.
239 The Upper Layer Interface (Message Handler)
240 -------------------------------------------
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.
248 Watching For Interfaces
250 When your code comes up, the IPMI driver may or may not have detected
251 if IPMI devices exist.  So you might have to defer your setup until
252 the device is detected, or you might be able to do it immediately.
253 To handle this, and to allow for discovery, you register an SMI
254 watcher with ipmi_smi_watcher_register() to iterate over interfaces
255 and tell you when they come and go.
258 Creating the User
260 To user the message handler, you must first create a user using
261 ipmi_create_user.  The interface number specifies which SMI you want
262 to connect to, and you must supply callback functions to be called
263 when data comes in.  The callback function can run at interrupt level,
264 so be careful using the callbacks.  This also allows to you pass in a
265 piece of data, the handler_data, that will be passed back to you on
266 all calls.
268 Once you are done, call ipmi_destroy_user() to get rid of the user.
270 From userland, opening the device automatically creates a user, and
271 closing the device automatically destroys the user.
274 Messaging
276 To send a message from kernel-land, the ipmi_request_settime() call does
277 pretty much all message handling.  Most of the parameter are
278 self-explanatory.  However, it takes a "msgid" parameter.  This is NOT
279 the sequence number of messages.  It is simply a long value that is
280 passed back when the response for the message is returned.  You may
281 use it for anything you like.
283 Responses come back in the function pointed to by the ipmi_recv_hndl
284 field of the "handler" that you passed in to ipmi_create_user().
285 Remember again, these may be running at interrupt level.  Remember to
286 look at the receive type, too.
288 From userland, you fill out an ipmi_req_t structure and use the
289 IPMICTL_SEND_COMMAND ioctl.  For incoming stuff, you can use select()
290 or poll() to wait for messages to come in.  However, you cannot use
291 read() to get them, you must call the IPMICTL_RECEIVE_MSG with the
292 ipmi_recv_t structure to actually get the message.  Remember that you
293 must supply a pointer to a block of data in the field, and
294 you must fill in the msg.data_len field with the size of the data.
295 This gives the receiver a place to actually put the message.
297 If the message cannot fit into the data you provide, you will get an
298 EMSGSIZE error and the driver will leave the data in the receive
299 queue.  If you want to get it and have it truncate the message, us
302 When you send a command (which is defined by the lowest-order bit of
303 the netfn per the IPMI spec) on the IPMB bus, the driver will
304 automatically assign the sequence number to the command and save the
305 command.  If the response is not receive in the IPMI-specified 5
306 seconds, it will generate a response automatically saying the command
307 timed out.  If an unsolicited response comes in (if it was after 5
308 seconds, for instance), that response will be ignored.
310 In kernelland, after you receive a message and are done with it, you
311 MUST call ipmi_free_recv_msg() on it, or you will leak messages.  Note
312 that you should NEVER mess with the "done" field of a message, that is
313 required to properly clean up the message.
315 Note that when sending, there is an ipmi_request_supply_msgs() call
316 that lets you supply the smi and receive message.  This is useful for
317 pieces of code that need to work even if the system is out of buffers
318 (the watchdog timer uses this, for instance).  You supply your own
319 buffer and own free routines.  This is not recommended for normal use,
320 though, since it is tricky to manage your own buffers.
323 Events and Incoming Commands
325 The driver takes care of polling for IPMI events and receiving
326 commands (commands are messages that are not responses, they are
327 commands that other things on the IPMB bus have sent you).  To receive
328 these, you must register for them, they will not automatically be sent
329 to you.
331 To receive events, you must call ipmi_set_gets_events() and set the
332 "val" to non-zero.  Any events that have been received by the driver
333 since startup will immediately be delivered to the first user that
334 registers for events.  After that, if multiple users are registered
335 for events, they will all receive all events that come in.
337 For receiving commands, you have to individually register commands you
338 want to receive.  Call ipmi_register_for_cmd() and supply the netfn
339 and command name for each command you want to receive.  You also
340 specify a bitmask of the channels you want to receive the command from
341 (or use IPMI_CHAN_ALL for all channels if you don't care).  Only one
342 user may be registered for each netfn/cmd/channel, but different users
343 may register for different commands, or the same command if the
344 channel bitmasks do not overlap.
346 From userland, equivalent IOCTLs are provided to do these functions.
349 The Lower Layer (SMI) Interface
350 -------------------------------
352 As mentioned before, multiple SMI interfaces may be registered to the
353 message handler, each of these is assigned an interface number when
354 they register with the message handler.  They are generally assigned
355 in the order they register, although if an SMI unregisters and then
356 another one registers, all bets are off.
358 The ipmi_smi.h defines the interface for management interfaces, see
359 that for more details.
362 The SI Driver
363 -------------
365 The SI driver allows KCS, BT, and SMIC interfaces to be configured
366 in the system.  It discovers interfaces through a host of different
367 methods, depending on the system.
369 You can specify up to four interfaces on the module load line and
370 control some module parameters:
372   modprobe ipmi_si.o type=<type1>,<type2>....
373        ports=<port1>,<port2>... addrs=<addr1>,<addr2>...
374        irqs=<irq1>,<irq2>...
375        regspacings=<sp1>,<sp2>,... regsizes=<size1>,<size2>,...
376        regshifts=<shift1>,<shift2>,...
377        slave_addrs=<addr1>,<addr2>,...
378        force_kipmid=<enable1>,<enable2>,...
379        kipmid_max_busy_us=<ustime1>,<ustime2>,...
380        unload_when_empty=[0|1]
381        trydmi=[0|1] tryacpi=[0|1]
382        tryplatform=[0|1] trypci=[0|1]
384 Each of these except try... items is a list, the first item for the
385 first interface, second item for the second interface, etc.
387 The si_type may be either "kcs", "smic", or "bt".  If you leave it blank, it
388 defaults to "kcs".
390 If you specify addrs as non-zero for an interface, the driver will
391 use the memory address given as the address of the device.  This
392 overrides si_ports.
394 If you specify ports as non-zero for an interface, the driver will
395 use the I/O port given as the device address.
397 If you specify irqs as non-zero for an interface, the driver will
398 attempt to use the given interrupt for the device.
400 The other try... items disable discovery by their corresponding
401 names.  These are all enabled by default, set them to zero to disable
402 them.  The tryplatform disables openfirmware.
404 The next three parameters have to do with register layout.  The
405 registers used by the interfaces may not appear at successive
406 locations and they may not be in 8-bit registers.  These parameters
407 allow the layout of the data in the registers to be more precisely
408 specified.
410 The regspacings parameter give the number of bytes between successive
411 register start addresses.  For instance, if the regspacing is set to 4
412 and the start address is 0xca2, then the address for the second
413 register would be 0xca6.  This defaults to 1.
415 The regsizes parameter gives the size of a register, in bytes.  The
416 data used by IPMI is 8-bits wide, but it may be inside a larger
417 register.  This parameter allows the read and write type to specified.
418 It may be 1, 2, 4, or 8.  The default is 1.
420 Since the register size may be larger than 32 bits, the IPMI data may not
421 be in the lower 8 bits.  The regshifts parameter give the amount to shift
422 the data to get to the actual IPMI data.
424 The slave_addrs specifies the IPMI address of the local BMC.  This is
425 usually 0x20 and the driver defaults to that, but in case it's not, it
426 can be specified when the driver starts up.
428 The force_ipmid parameter forcefully enables (if set to 1) or disables
429 (if set to 0) the kernel IPMI daemon.  Normally this is auto-detected
430 by the driver, but systems with broken interrupts might need an enable,
431 or users that don't want the daemon (don't need the performance, don't
432 want the CPU hit) can disable it.
434 If unload_when_empty is set to 1, the driver will be unloaded if it
435 doesn't find any interfaces or all the interfaces fail to work.  The
436 default is one.  Setting to 0 is useful with the hotmod, but is
437 obviously only useful for modules.
439 When compiled into the kernel, the parameters can be specified on the
440 kernel command line as:
442   ipmi_si.type=<type1>,<type2>...
443        ipmi_si.ports=<port1>,<port2>... ipmi_si.addrs=<addr1>,<addr2>...
444        ipmi_si.irqs=<irq1>,<irq2>...
445        ipmi_si.regspacings=<sp1>,<sp2>,...
446        ipmi_si.regsizes=<size1>,<size2>,...
447        ipmi_si.regshifts=<shift1>,<shift2>,...
448        ipmi_si.slave_addrs=<addr1>,<addr2>,...
449        ipmi_si.force_kipmid=<enable1>,<enable2>,...
450        ipmi_si.kipmid_max_busy_us=<ustime1>,<ustime2>,...
452 It works the same as the module parameters of the same names.
454 If your IPMI interface does not support interrupts and is a KCS or
455 SMIC interface, the IPMI driver will start a kernel thread for the
456 interface to help speed things up.  This is a low-priority kernel
457 thread that constantly polls the IPMI driver while an IPMI operation
458 is in progress.  The force_kipmid module parameter will all the user to
459 force this thread on or off.  If you force it off and don't have
460 interrupts, the driver will run VERY slowly.  Don't blame me,
461 these interfaces suck.
463 Unfortunately, this thread can use a lot of CPU depending on the
464 interface's performance.  This can waste a lot of CPU and cause
465 various issues with detecting idle CPU and using extra power.  To
466 avoid this, the kipmid_max_busy_us sets the maximum amount of time, in
467 microseconds, that kipmid will spin before sleeping for a tick.  This
468 value sets a balance between performance and CPU waste and needs to be
469 tuned to your needs.  Maybe, someday, auto-tuning will be added, but
470 that's not a simple thing and even the auto-tuning would need to be
471 tuned to the user's desired performance.
473 The driver supports a hot add and remove of interfaces.  This way,
474 interfaces can be added or removed after the kernel is up and running.
475 This is done using /sys/modules/ipmi_si/parameters/hotmod, which is a
476 write-only parameter.  You write a string to this interface.  The string
477 has the format:
478    <op1>[:op2[:op3...]]
479 The "op"s are:
480    add|remove,kcs|bt|smic,mem|i/o,<address>[,<opt1>[,<opt2>[,...]]]
481 You can specify more than one interface on the line.  The "opt"s are:
482    rsp=<regspacing>
483    rsi=<regsize>
484    rsh=<regshift>
485    irq=<irq>
486    ipmb=<ipmb slave addr>
487 and these have the same meanings as discussed above.  Note that you
488 can also use this on the kernel command line for a more compact format
489 for specifying an interface.  Note that when removing an interface,
490 only the first three parameters (si type, address type, and address)
491 are used for the comparison.  Any options are ignored for removing.
493 The SMBus Driver (SSIF)
494 -----------------------
496 The SMBus driver allows up to 4 SMBus devices to be configured in the
497 system.  By default, the driver will only register with something it
498 finds in DMI or ACPI tables.  You can change this
499 at module load time (for a module) with:
501   modprobe ipmi_ssif.o
502         addr=<i2caddr1>[,<i2caddr2>[,...]]
503         adapter=<adapter1>[,<adapter2>[...]]
504         dbg=<flags1>,<flags2>...
505         slave_addrs=<addr1>,<addr2>,...
506         tryacpi=[0|1] trydmi=[0|1]
507         [dbg_probe=1]
509 The addresses are normal I2C addresses.  The adapter is the string
510 name of the adapter, as shown in /sys/class/i2c-adapter/i2c-<n>/name.
511 It is *NOT* i2c-<n> itself.  Also, the comparison is done ignoring
512 spaces, so if the name is "This is an I2C chip" you can say
513 adapter_name=ThisisanI2cchip.  This is because it's hard to pass in
514 spaces in kernel parameters.
516 The debug flags are bit flags for each BMC found, they are:
517 IPMI messages: 1, driver state: 2, timing: 4, I2C probe: 8
519 The tryxxx parameters can be used to disable detecting interfaces
520 from various sources.
522 Setting dbg_probe to 1 will enable debugging of the probing and
523 detection process for BMCs on the SMBusses.
525 The slave_addrs specifies the IPMI address of the local BMC.  This is
526 usually 0x20 and the driver defaults to that, but in case it's not, it
527 can be specified when the driver starts up.
529 Discovering the IPMI compliant BMC on the SMBus can cause devices on
530 the I2C bus to fail. The SMBus driver writes a "Get Device ID" IPMI
531 message as a block write to the I2C bus and waits for a response.
532 This action can be detrimental to some I2C devices. It is highly
533 recommended that the known I2C address be given to the SMBus driver in
534 the smb_addr parameter unless you have DMI or ACPI data to tell the
535 driver what to use.
537 When compiled into the kernel, the addresses can be specified on the
538 kernel command line as:
540   ipmb_ssif.addr=<i2caddr1>[,<i2caddr2>[...]]
541         ipmi_ssif.adapter=<adapter1>[,<adapter2>[...]]
542         ipmi_ssif.dbg=<flags1>[,<flags2>[...]]
543         ipmi_ssif.dbg_probe=1
544         ipmi_ssif.slave_addrs=<addr1>[,<addr2>[...]]
545         ipmi_ssif.tryacpi=[0|1] ipmi_ssif.trydmi=[0|1]
547 These are the same options as on the module command line.
549 The I2C driver does not support non-blocking access or polling, so
550 this driver cannod to IPMI panic events, extend the watchdog at panic
551 time, or other panic-related IPMI functions without special kernel
552 patches and driver modifications.  You can get those at the openipmi
553 web page.
555 The driver supports a hot add and remove of interfaces through the I2C
556 sysfs interface.
558 Other Pieces
559 ------------
561 Get the detailed info related with the IPMI device
562 --------------------------------------------------
564 Some users need more detailed information about a device, like where
565 the address came from or the raw base device for the IPMI interface.
566 You can use the IPMI smi_watcher to catch the IPMI interfaces as they
567 come or go, and to grab the information, you can use the function
568 ipmi_get_smi_info(), which returns the following structure:
570 struct ipmi_smi_info {
571         enum ipmi_addr_src addr_src;
572         struct device *dev;
573         union {
574                 struct {
575                         void *acpi_handle;
576                 } acpi_info;
577         } addr_info;
578 };
580 Currently special info for only for SI_ACPI address sources is
581 returned.  Others may be added as necessary.
583 Note that the dev pointer is included in the above structure, and
584 assuming ipmi_smi_get_info returns success, you must call put_device
585 on the dev pointer.
588 Watchdog
589 --------
591 A watchdog timer is provided that implements the Linux-standard
592 watchdog timer interface.  It has three module parameters that can be
593 used to control it:
595   modprobe ipmi_watchdog timeout=<t> pretimeout=<t> action=<action type>
596       preaction=<preaction type> preop=<preop type> start_now=x
597       nowayout=x ifnum_to_use=n panic_wdt_timeout=<t>
599 ifnum_to_use specifies which interface the watchdog timer should use.
600 The default is -1, which means to pick the first one registered.
602 The timeout is the number of seconds to the action, and the pretimeout
603 is the amount of seconds before the reset that the pre-timeout panic will
604 occur (if pretimeout is zero, then pretimeout will not be enabled).  Note
605 that the pretimeout is the time before the final timeout.  So if the
606 timeout is 50 seconds and the pretimeout is 10 seconds, then the pretimeout
607 will occur in 40 second (10 seconds before the timeout). The panic_wdt_timeout
608 is the value of timeout which is set on kernel panic, in order to let actions
609 such as kdump to occur during panic.
611 The action may be "reset", "power_cycle", or "power_off", and
612 specifies what to do when the timer times out, and defaults to
613 "reset".
615 The preaction may be "pre_smi" for an indication through the SMI
616 interface, "pre_int" for an indication through the SMI with an
617 interrupts, and "pre_nmi" for a NMI on a preaction.  This is how
618 the driver is informed of the pretimeout.
620 The preop may be set to "preop_none" for no operation on a pretimeout,
621 "preop_panic" to set the preoperation to panic, or "preop_give_data"
622 to provide data to read from the watchdog device when the pretimeout
623 occurs.  A "pre_nmi" setting CANNOT be used with "preop_give_data"
624 because you can't do data operations from an NMI.
626 When preop is set to "preop_give_data", one byte comes ready to read
627 on the device when the pretimeout occurs.  Select and fasync work on
628 the device, as well.
630 If start_now is set to 1, the watchdog timer will start running as
631 soon as the driver is loaded.
633 If nowayout is set to 1, the watchdog timer will not stop when the
634 watchdog device is closed.  The default value of nowayout is true
635 if the CONFIG_WATCHDOG_NOWAYOUT option is enabled, or false if not.
637 When compiled into the kernel, the kernel command line is available
638 for configuring the watchdog:
640   ipmi_watchdog.timeout=<t> ipmi_watchdog.pretimeout=<t>
641         ipmi_watchdog.action=<action type>
642         ipmi_watchdog.preaction=<preaction type>
643         ipmi_watchdog.preop=<preop type>
644         ipmi_watchdog.start_now=x
645         ipmi_watchdog.nowayout=x
646         ipmi_watchdog.panic_wdt_timeout=<t>
648 The options are the same as the module parameter options.
650 The watchdog will panic and start a 120 second reset timeout if it
651 gets a pre-action.  During a panic or a reboot, the watchdog will
652 start a 120 timer if it is running to make sure the reboot occurs.
654 Note that if you use the NMI preaction for the watchdog, you MUST NOT
655 use the nmi watchdog.  There is no reasonable way to tell if an NMI
656 comes from the IPMI controller, so it must assume that if it gets an
657 otherwise unhandled NMI, it must be from IPMI and it will panic
658 immediately.
660 Once you open the watchdog timer, you must write a 'V' character to the
661 device to close it, or the timer will not stop.  This is a new semantic
662 for the driver, but makes it consistent with the rest of the watchdog
663 drivers in Linux.
666 Panic Timeouts
667 --------------
669 The OpenIPMI driver supports the ability to put semi-custom and custom
670 events in the system event log if a panic occurs.  if you enable the
671 'Generate a panic event to all BMCs on a panic' option, you will get
672 one event on a panic in a standard IPMI event format.  If you enable
673 the 'Generate OEM events containing the panic string' option, you will
674 also get a bunch of OEM events holding the panic string.
677 The field settings of the events are:
678 * Generator ID: 0x21 (kernel)
679 * EvM Rev: 0x03 (this event is formatting in IPMI 1.0 format)
680 * Sensor Type: 0x20 (OS critical stop sensor)
681 * Sensor #: The first byte of the panic string (0 if no panic string)
682 * Event Dir | Event Type: 0x6f (Assertion, sensor-specific event info)
683 * Event Data 1: 0xa1 (Runtime stop in OEM bytes 2 and 3)
684 * Event data 2: second byte of panic string
685 * Event data 3: third byte of panic string
686 See the IPMI spec for the details of the event layout.  This event is
687 always sent to the local management controller.  It will handle routing
688 the message to the right place
690 Other OEM events have the following format:
691 Record ID (bytes 0-1): Set by the SEL.
692 Record type (byte 2): 0xf0 (OEM non-timestamped)
693 byte 3: The slave address of the card saving the panic
694 byte 4: A sequence number (starting at zero)
695 The rest of the bytes (11 bytes) are the panic string.  If the panic string
696 is longer than 11 bytes, multiple messages will be sent with increasing
697 sequence numbers.
699 Because you cannot send OEM events using the standard interface, this
700 function will attempt to find an SEL and add the events there.  It
701 will first query the capabilities of the local management controller.
702 If it has an SEL, then they will be stored in the SEL of the local
703 management controller.  If not, and the local management controller is
704 an event generator, the event receiver from the local management
705 controller will be queried and the events sent to the SEL on that
706 device.  Otherwise, the events go nowhere since there is nowhere to
707 send them.
710 Poweroff
711 --------
713 If the poweroff capability is selected, the IPMI driver will install
714 a shutdown function into the standard poweroff function pointer.  This
715 is in the ipmi_poweroff module.  When the system requests a powerdown,
716 it will send the proper IPMI commands to do this.  This is supported on
717 several platforms.
719 There is a module parameter named "poweroff_powercycle" that may
720 either be zero (do a power down) or non-zero (do a power cycle, power
721 the system off, then power it on in a few seconds).  Setting
722 ipmi_poweroff.poweroff_control=x will do the same thing on the kernel
723 command line.  The parameter is also available via the proc filesystem
724 in /proc/sys/dev/ipmi/poweroff_powercycle.  Note that if the system
725 does not support power cycling, it will always do the power off.
727 The "ifnum_to_use" parameter specifies which interface the poweroff
728 code should use.  The default is -1, which means to pick the first one
729 registered.
731 Note that if you have ACPI enabled, the system will prefer using ACPI to
732 power off.

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