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>