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+ The Linux IPMI Driver
+ Corey Minyard
+The Intelligent Platform Management Interface, or IPMI, is a
+standard for controlling intelligent devices that monitor a system.
+It provides for dynamic discovery of sensors in the system and the
+ability to monitor the sensors and be informed when the sensor's
+values change or go outside certain boundaries. It also has a
+standardized database for field-replacable units (FRUs) and a watchdog
+To use this, you need an interface to an IPMI controller in your
+system (called a Baseboard Management Controller, or BMC) and
+management software that can use the IPMI system.
+This document describes how to use the IPMI driver for Linux. If you
+are not familiar with IPMI itself, see the web site at
+http://www.intel.com/design/servers/ipmi/index.htm. IPMI is a big
+subject and I can't cover it all here!
+The LinuxIPMI driver is modular, which means you have to pick several
+things to have it work right depending on your hardware. Most of
+these are available in the 'Character Devices' menu.
+No matter what, you must pick 'IPMI top-level message handler' to use
+IPMI. What you do beyond that depends on your needs and hardware.
+The message handler does not provide any user-level interfaces.
+Kernel code (like the watchdog) can still use it. If you need access
+from userland, you need to select 'Device interface for IPMI' if you
+want access through a device driver. Another interface is also
+available, you may select 'IPMI sockets' in the 'Networking Support'
+main menu. This provides a socket interface to IPMI. You may select
+both of these at the same time, they will both work together.
+The driver interface depends on your hardware. If you have a board
+with a standard interface (These will generally be either "KCS",
+"SMIC", or "BT", consult your hardware manual), choose the 'IPMI SI
+handler' option. A driver also exists for direct I2C access to the
+IPMI management controller. Some boards support this, but it is
+unknown if it will work on every board. For this, choose 'IPMI SMBus
+handler', but be ready to try to do some figuring to see if it will
+There is also a KCS-only driver interface supplied, but it is
+depracated in favor of the SI interface.
+You should generally enable ACPI on your system, as systems with IPMI
+should have ACPI tables describing them.
+If you have a standard interface and the board manufacturer has done
+their job correctly, the IPMI controller should be automatically
+detect (via ACPI or SMBIOS tables) and should just work. Sadly, many
+boards do not have this information. The driver attempts standard
+defaults, but they may not work. If you fall into this situation, you
+need to read the section below named 'The SI Driver' on how to
+hand-configure your system.
+IPMI defines a standard watchdog timer. You can enable this with the
+'IPMI Watchdog Timer' config option. If you compile the driver into
+the kernel, then via a kernel command-line option you can have the
+watchdog timer start as soon as it intitializes. It also have a lot
+of other options, see the 'Watchdog' section below for more details.
+Note that you can also have the watchdog continue to run if it is
+closed (by default it is disabled on close). Go into the 'Watchdog
+Cards' menu, enable 'Watchdog Timer Support', and enable the option
+'Disable watchdog shutdown on close'.
+The Linux IPMI driver is designed to be very modular and flexible, you
+only need to take the pieces you need and you can use it in many
+different ways. Because of that, it's broken into many chunks of
+code. These chunks are:
+ipmi_msghandler - This is the central piece of software for the IPMI
+system. It handles all messages, message timing, and responses. The
+IPMI users tie into this, and the IPMI physical interfaces (called
+System Management Interfaces, or SMIs) also tie in here. This
+provides the kernelland interface for IPMI, but does not provide an
+interface for use by application processes.
+ipmi_devintf - This provides a userland IOCTL interface for the IPMI
+driver, each open file for this device ties in to the message handler
+as an IPMI user.
+ipmi_si - A driver for various system interfaces. This supports
+KCS, SMIC, and may support BT in the future. Unless you have your own
+custom interface, you probably need to use this.
+ipmi_smb - A driver for accessing BMCs on the SMBus. It uses the
+I2C kernel driver's SMBus interfaces to send and receive IPMI messages
+over the SMBus.
+af_ipmi - A network socket interface to IPMI. This doesn't take up
+a character device in your system.
+Note that the KCS-only interface ahs been removed.
+Much documentation for the interface is in the include files. The
+IPMI include files are:
+net/af_ipmi.h - Contains the socket interface.
+linux/ipmi.h - Contains the user interface and IOCTL interface for IPMI.
+linux/ipmi_smi.h - Contains the interface for system management interfaces
+(things that interface to IPMI controllers) to use.
+linux/ipmi_msgdefs.h - General definitions for base IPMI messaging.
+The IPMI addressing works much like IP addresses, you have an overlay
+to handle the different address types. The overlay is:
+ struct ipmi_addr
+ int addr_type;
+ short channel;
+ char data[IPMI_MAX_ADDR_SIZE];
+The addr_type determines what the address really is. The driver
+currently understands two different types of addresses.
+"System Interface" addresses are defined as:
+ struct ipmi_system_interface_addr
+ int addr_type;
+ short channel;
+and the type is IPMI_SYSTEM_INTERFACE_ADDR_TYPE. This is used for talking
+straight to the BMC on the current card. The channel must be
+Messages that are destined to go out on the IPMB bus use the
+IPMI_IPMB_ADDR_TYPE address type. The format is
+ struct ipmi_ipmb_addr
+ int addr_type;
+ short channel;
+ unsigned char slave_addr;
+ unsigned char lun;
+The "channel" here is generally zero, but some devices support more
+than one channel, it corresponds to the channel as defined in the IPMI
+Messages are defined as:
+ unsigned char netfn;
+ unsigned char lun;
+ unsigned char cmd;
+ unsigned char *data;
+ int data_len;
+The driver takes care of adding/stripping the header information. The
+data portion is just the data to be send (do NOT put addressing info
+here) or the response. Note that the completion code of a response is
+the first item in "data", it is not stripped out because that is how
+all the messages are defined in the spec (and thus makes counting the
+offsets a little easier :-).
+When using the IOCTL interface from userland, you must provide a block
+of data for "data", fill it, and set data_len to the length of the
+block of data, even when receiving messages. Otherwise the driver
+will have no place to put the message.
+Messages coming up from the message handler in kernelland will come in
+ struct ipmi_recv_msg
+ struct list_head link;
+ /* The type of message as defined in the "Receive Types"
+ defines above. */
+ int recv_type;
+ ipmi_user_t *user;
+ struct ipmi_addr addr;
+ long msgid;
+ struct ipmi_msg msg;
+ /* Call this when done with the message. It will presumably free
+ the message and do any other necessary cleanup. */
+ void (*done)(struct ipmi_recv_msg *msg);
+ /* Place-holder for the data, don't make any assumptions about
+ the size or existence of this, since it may change. */
+ unsigned char msg_data[IPMI_MAX_MSG_LENGTH];
+You should look at the receive type and handle the message
+The Upper Layer Interface (Message Handler)
+The upper layer of the interface provides the users with a consistent
+view of the IPMI interfaces. It allows multiple SMI interfaces to be
+addressed (because some boards actually have multiple BMCs on them)
+and the user should not have to care what type of SMI is below them.
+Creating the User
+To user the message handler, you must first create a user using
+ipmi_create_user. The interface number specifies which SMI you want
+to connect to, and you must supply callback functions to be called
+when data comes in. The callback function can run at interrupt level,
+so be careful using the callbacks. This also allows to you pass in a
+piece of data, the handler_data, that will be passed back to you on
+Once you are done, call ipmi_destroy_user() to get rid of the user.
+From userland, opening the device automatically creates a user, and
+closing the device automatically destroys the user.
+To send a message from kernel-land, the ipmi_request() call does
+pretty much all message handling. Most of the parameter are
+self-explanatory. However, it takes a "msgid" parameter. This is NOT
+the sequence number of messages. It is simply a long value that is
+passed back when the response for the message is returned. You may
+use it for anything you like.
+Responses come back in the function pointed to by the ipmi_recv_hndl
+field of the "handler" that you passed in to ipmi_create_user().
+Remember again, these may be running at interrupt level. Remember to
+look at the receive type, too.
+From userland, you fill out an ipmi_req_t structure and use the
+IPMICTL_SEND_COMMAND ioctl. For incoming stuff, you can use select()
+or poll() to wait for messages to come in. However, you cannot use
+read() to get them, you must call the IPMICTL_RECEIVE_MSG with the
+ipmi_recv_t structure to actually get the message. Remember that you
+must supply a pointer to a block of data in the msg.data field, and
+you must fill in the msg.data_len field with the size of the data.
+This gives the receiver a place to actually put the message.
+If the message cannot fit into the data you provide, you will get an
+EMSGSIZE error and the driver will leave the data in the receive
+queue. If you want to get it and have it truncate the message, us
+the IPMICTL_RECEIVE_MSG_TRUNC ioctl.
+When you send a command (which is defined by the lowest-order bit of
+the netfn per the IPMI spec) on the IPMB bus, the driver will
+automatically assign the sequence number to the command and save the
+command. If the response is not receive in the IPMI-specified 5
+seconds, it will generate a response automatically saying the command
+timed out. If an unsolicited response comes in (if it was after 5
+seconds, for instance), that response will be ignored.
+In kernelland, after you receive a message and are done with it, you
+MUST call ipmi_free_recv_msg() on it, or you will leak messages. Note
+that you should NEVER mess with the "done" field of a message, that is
+required to properly clean up the message.
+Note that when sending, there is an ipmi_request_supply_msgs() call
+that lets you supply the smi and receive message. This is useful for
+pieces of code that need to work even if the system is out of buffers
+(the watchdog timer uses this, for instance). You supply your own
+buffer and own free routines. This is not recommended for normal use,
+though, since it is tricky to manage your own buffers.
+Events and Incoming Commands
+The driver takes care of polling for IPMI events and receiving
+commands (commands are messages that are not responses, they are
+commands that other things on the IPMB bus have sent you). To receive
+these, you must register for them, they will not automatically be sent
+To receive events, you must call ipmi_set_gets_events() and set the
+"val" to non-zero. Any events that have been received by the driver
+since startup will immediately be delivered to the first user that
+registers for events. After that, if multiple users are registered
+for events, they will all receive all events that come in.
+For receiving commands, you have to individually register commands you
+want to receive. Call ipmi_register_for_cmd() and supply the netfn
+and command name for each command you want to receive. Only one user
+may be registered for each netfn/cmd, but different users may register
+for different commands.
+From userland, equivalent IOCTLs are provided to do these functions.
+The Lower Layer (SMI) Interface
+As mentioned before, multiple SMI interfaces may be registered to the
+message handler, each of these is assigned an interface number when
+they register with the message handler. They are generally assigned
+in the order they register, although if an SMI unregisters and then
+another one registers, all bets are off.
+The ipmi_smi.h defines the interface for management interfaces, see
+that for more details.
+The SI Driver
+The SI driver allows up to 4 KCS or SMIC interfaces to be configured
+in the system. By default, scan the ACPI tables for interfaces, and
+if it doesn't find any the driver will attempt to register one KCS
+interface at the spec-specified I/O port 0xca2 without interrupts.
+You can change this at module load time (for a module) with:
+ modprobe ipmi_si.o type=<type1>,<type2>....
+ ports=<port1>,<port2>... addrs=<addr1>,<addr2>...
+ irqs=<irq1>,<irq2>... trydefaults=[0|1]
+ regspacings=<sp1>,<sp2>,... regsizes=<size1>,<size2>,...
+Each of these except si_trydefaults is a list, the first item for the
+first interface, second item for the second interface, etc.
+The si_type may be either "kcs", "smic", or "bt". If you leave it blank, it
+defaults to "kcs".
+If you specify si_addrs as non-zero for an interface, the driver will
+use the memory address given as the address of the device. This
+If you specify si_ports as non-zero for an interface, the driver will
+use the I/O port given as the device address.
+If you specify si_irqs as non-zero for an interface, the driver will
+attempt to use the given interrupt for the device.
+si_trydefaults sets whether the standard IPMI interface at 0xca2 and
+any interfaces specified by ACPE are tried. By default, the driver
+tries it, set this value to zero to turn this off.
+The next three parameters have to do with register layout. The
+registers used by the interfaces may not appear at successive
+locations and they may not be in 8-bit registers. These parameters
+allow the layout of the data in the registers to be more precisely
+The regspacings parameter give the number of bytes between successive
+register start addresses. For instance, if the regspacing is set to 4
+and the start address is 0xca2, then the address for the second
+register would be 0xca6. This defaults to 1.
+The regsizes parameter gives the size of a register, in bytes. The
+data used by IPMI is 8-bits wide, but it may be inside a larger
+register. This parameter allows the read and write type to specified.
+It may be 1, 2, 4, or 8. The default is 1.
+Since the register size may be larger than 32 bits, the IPMI data may not
+be in the lower 8 bits. The regshifts parameter give the amount to shift
+the data to get to the actual IPMI data.
+The slave_addrs specifies the IPMI address of the local BMC. This is
+usually 0x20 and the driver defaults to that, but in case it's not, it
+can be specified when the driver starts up.
+When compiled into the kernel, the addresses can be specified on the
+kernel command line as:
+ ipmi_si.ports=<port1>,<port2>... ipmi_si.addrs=<addr1>,<addr2>...
+ ipmi_si.irqs=<irq1>,<irq2>... ipmi_si.trydefaults=[0|1]
+It works the same as the module parameters of the same names.
+By default, the driver will attempt to detect any device specified by
+ACPI, and if none of those then a KCS device at the spec-specified
+0xca2. If you want to turn this off, set the "trydefaults" option to
+If you have high-res timers compiled into the kernel, the driver will
+use them to provide much better performance. Note that if you do not
+have high-res timers enabled in the kernel and you don't have
+interrupts enabled, the driver will run VERY slowly. Don't blame me,
+these interfaces suck.
+The SMBus Driver
+The SMBus driver allows up to 4 SMBus devices to be configured in the
+system. By default, the driver will register any SMBus interfaces it finds
+in the I2C address range of 0x20 to 0x4f on any adapter. You can change this
+at module load time (for a module) with:
+ modprobe ipmi_smb.o
+ [defaultprobe=0] [dbg_probe=1]
+The addresses are specified in pairs, the first is the adapter ID and the
+second is the I2C address on that adapter.
+The debug flags are bit flags for each BMC found, they are:
+IPMI messages: 1, driver state: 2, timing: 4, I2C probe: 8
+Setting smb_defaultprobe to zero disabled the default probing of SMBus
+interfaces at address range 0x20 to 0x4f. This means that only the
+BMCs specified on the smb_addr line will be detected.
+Setting smb_dbg_probe to 1 will enable debugging of the probing and
+detection process for BMCs on the SMBusses.
+Discovering the IPMI compilant BMC on the SMBus can cause devices
+on the I2C bus to fail. The SMBus driver writes a "Get Device ID" IPMI
+message as a block write to the I2C bus and waits for a response.
+This action can be detrimental to some I2C devices. It is highly recommended
+that the known I2c address be given to the SMBus driver in the smb_addr
+parameter. The default adrress range will not be used when a smb_addr
+parameter is provided.
+When compiled into the kernel, the addresses can be specified on the
+kernel command line as:
+ ipmi_smb.defaultprobe=0 ipmi_smb.dbg_probe=1
+These are the same options as on the module command line.
+Note that you might need some I2C changes if CONFIG_IPMI_PANIC_EVENT
+is enabled along with this, so the I2C driver knows to run to
+completion during sending a panic event.
+A watchdog timer is provided that implements the Linux-standard
+watchdog timer interface. It has three module parameters that can be
+used to control it:
+ modprobe ipmi_watchdog timeout=<t> pretimeout=<t> action=<action type>
+ preaction=<preaction type> preop=<preop type> start_now=x
+The timeout is the number of seconds to the action, and the pretimeout
+is the amount of seconds before the reset that the pre-timeout panic will
+occur (if pretimeout is zero, then pretimeout will not be enabled). Note
+that the pretimeout is the time before the final timeout. So if the
+timeout is 50 seconds and the pretimeout is 10 seconds, then the pretimeout
+will occur in 40 second (10 seconds before the timeout).
+The action may be "reset", "power_cycle", or "power_off", and
+specifies what to do when the timer times out, and defaults to
+The preaction may be "pre_smi" for an indication through the SMI
+interface, "pre_int" for an indication through the SMI with an
+interrupts, and "pre_nmi" for a NMI on a preaction. This is how
+the driver is informed of the pretimeout.
+The preop may be set to "preop_none" for no operation on a pretimeout,
+"preop_panic" to set the preoperation to panic, or "preop_give_data"
+to provide data to read from the watchdog device when the pretimeout
+occurs. A "pre_nmi" setting CANNOT be used with "preop_give_data"
+because you can't do data operations from an NMI.
+When preop is set to "preop_give_data", one byte comes ready to read
+on the device when the pretimeout occurs. Select and fasync work on
+the device, as well.
+If start_now is set to 1, the watchdog timer will start running as
+soon as the driver is loaded.
+If nowayout is set to 1, the watchdog timer will not stop when the
+watchdog device is closed. The default value of nowayout is true
+if the CONFIG_WATCHDOG_NOWAYOUT option is enabled, or false if not.
+When compiled into the kernel, the kernel command line is available
+for configuring the watchdog:
+ ipmi_watchdog.timeout=<t> ipmi_watchdog.pretimeout=<t>
+ ipmi_watchdog.action=<action type>
+ ipmi_watchdog.preaction=<preaction type>
+ ipmi_watchdog.preop=<preop type>
+The options are the same as the module parameter options.
+The watchdog will panic and start a 120 second reset timeout if it
+gets a pre-action. During a panic or a reboot, the watchdog will
+start a 120 timer if it is running to make sure the reboot occurs.
+Note that if you use the NMI preaction for the watchdog, you MUST
+NOT use nmi watchdog mode 1. If you use the NMI watchdog, you
+must use mode 2.
+Once you open the watchdog timer, you must write a 'V' character to the
+device to close it, or the timer will not stop. This is a new semantic
+for the driver, but makes it consistent with the rest of the watchdog
+drivers in Linux.