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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

timer.

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!

Basic Design

------------

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_kcs_drv - A driver for the KCS SMI.  Most system have a KCS

interface for IPMI.

Much documentation for the interface is in the include files.  The

IPMI include files are:

ipmi.h - Contains the user interface and IOCTL interface for IPMI.

ipmi_smi.h - Contains the interface for SMI drivers to use.

ipmi_msgdefs.h - General definitions for base IPMI messaging.

Addressing

----------

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

IPMI_BMC_CHANNEL.

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

spec.

Messages

--------

Messages are defined as:

struct ipmi_msg

{

        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

as:

  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

appropriately.

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

all calls.

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.

Messaging

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 you.

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 SMIs, see that for more

details.

The KCS Driver

--------------

The KCS driver allows up to 4 KCS interfaces to be configured in the

system.  By default, the driver will 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:

  insmod ipmi_kcs_drv.o kcs_ports=,... kcs_addrs=,

       kcs_irqs=,... kcs_trydefaults=[0|1]

The KCS driver supports two types of interfaces, ports (for I/O port

based KCS interfaces) and memory addresses (for KCS interfaces in

memory).  The driver will support both of them simultaneously, setting

the port to zero (or just not specifying it) will allow the memory

address to be used.  The port will override the memory address if it

is specified and non-zero.  kcs_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.

When compiled into the kernel, the addresses can be specified on the

kernel command line as:

  ipmi_kcs=:,:....,[nodefault]

The  values is either "p" or "m" for port or memory

addresses.  So for instance, a KCS interface at port 0xca2 using

interrupt 9 and a memory interface at address 0xf9827341 with no

interrupt would be specified "ipmi_kcs=p0xca2:9,m0xf9827341".

If you specify zero for in irq or don't specify it, the driver will

run polled unless the software can detect the interrupt to use in the

ACPI tables.

By default, the driver will attempt to detect a KCS device at the

spec-specified 0xca2 address and any address specified by ACPI.  If

you want to turn this off, use the "nodefault" option.

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,

the KCS interface sucks.

Other Pieces

------------

Watchdog

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:

  insmod ipmi_watchdog timeout= pretimeout= action=

      preaction= preop=

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).

The action may be "reset", "power_cycle", or "power_off", and

specifies what to do when the timer times out, and defaults to

"reset".

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.

When compiled into the kernel, the kernel command line is available

for configuring the watchdog:

  ipmi_wdog=[,[,[,....]]]

The options are the actions and preaction above (if an option

controlling the same thing is specified twice, the last is taken).  An

options "start_now" is also there, if included, the watchdog will

start running immediately when all the drivers are ready, it doesn't

have to have a user hooked up to start it.

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.