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 <
[email protected]>
FreeBSD 14.1-RELEASE-p8 March 2, 2018 FreeBSD 14.1-RELEASE-p8