IMCSMB(4)              FreeBSD Kernel Interfaces Manual              IMCSMB(4)

NAME
     imcsmb - Intel integrated Memory Controller (iMC) SMBus controller driver

SYNOPSIS
     device pci
     device smbus
     device imcsmb

     Alternatively, to load the driver as a module at boot time, place the
     following line in loader.conf(5):

           imcsmb_load="YES"

DESCRIPTION
     The imcsmb driver provides smbus(4) support for the SMBus controller
     functionality in the integrated Memory Controllers (iMCs) embedded in
     Intel Sandybridge-Xeon, Ivybridge-Xeon, Haswell-Xeon, and Broadwell-Xeon
     CPUs.  Each CPU implements one or more iMCs, depending on the number of
     cores; each iMC implements two SMBus controllers (iMC-SMBs).  The iMC-
     SMBs are used by the iMCs to read configuration information from the
     DIMMs during POST.  They may also be used, by motherboard firmware or a
     BMC, to monitor the temperature of the DIMMs.

     The iMC-SMBs are not general-purpose SMBus controllers.  By their nature,
     they are only ever attached to DIMMs, so they implement only the SMBus
     operations need for communicating with DIMMs.  Specifically:

           -   READB
           -   READW
           -   WRITEB
           -   WRITEW

     A more detailed discussion of the hardware and driver architecture can be
     found at the top of sys/dev/imcsmb/imcsmb_pci.c.

WARNINGS
     As mentioned above, firmware might use the iMC-SMBs to read DIMM
     temperatures.  The public iMC documentation does not describe any sort of
     coordination mechanism to prevent requests from different sources -- such
     as the motherboard firmware, a BMC, or the operating system -- from
     interfering with each other.

     Therefore, it is highly recommended that developers contact the
     motherboard vendor for any board-specific instructions on how to disable
     and re-enable DIMM temperature monitoring.

     DIMM temperature monitoring should be disabled before returning from
     imcsmb_pci_request_bus(), and re-enabled before returning from
     imcsmb_pci_release_bus().  The driver includes comments to that effect at
     the appropriate locations.  The driver has been tested and shown to work,
     with only that type of modification, on certain motherboards from Intel.
     (Unfortunately, those modifications were based on material covered under
     a non-disclosure agreement, and therefore are not included in this
     driver.) The driver has also been tested and shown to work as-is on
     various motherboards from SuperMicro.

     The smb(4) driver will connect to the smbus(4) instances created by
     imcsmb.  However, since the IMC-SMBs are not general-purpose SMBus
     controllers, using smbmsg(8) with those smb(4) devices is not supported.

SEE ALSO
     jedec_dimm(4), smbus(4)

HISTORY
     The imcsmb driver first appeared in FreeBSD 12.0.

AUTHORS
     The imcsmb driver was originally written for Panasas by Joe Kloss.  It
     was substantially refactored, and this manual page was written, by
     Ravi Pokala <rpokala@freebsd.org>

FreeBSD 13.1-RELEASE-p6          March 2, 2018         FreeBSD 13.1-RELEASE-p6