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				.\"
				.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
				.\"
				.\" Copyright (c) 2018 Panasas
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				.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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				.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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				.\" $FreeBSD$
				.\"
				.Dd March 2, 2018
				.Dt IMCSMB 4
				.Os
				.Sh NAME
				.Nm imcsmb
				.Nd Intel integrated Memory Controller (iMC) SMBus controller driver
				.Sh SYNOPSIS
				.Cd device pci
				.Cd device smbus
				.Cd device imcsmb
				.Pp
				Alternatively, to load the driver as a module at boot time, place the following
				line in
				.Xr loader.conf 5 :
				.Bd -literal -offset indent
				imcsmb_load="YES"
				.Ed
				.Sh DESCRIPTION
				The
				.Nm
				driver provides
				.Xr 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.
				.Pp
				The iMC-SMBs are
				.Sy 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:
				.Pp
				.Bl -dash -offset indent -compact
				.It
				READB
				.It
				READW
				.It
				WRITEB
				.It
				WRITEW
				.El
				.Pp
				A more detailed discussion of the hardware and driver architecture can be found
				at the top of
				.Pa sys/dev/imcsmb/imcsmb_pci.c .
				.Sh 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.
				.Pp
				.Bf Sy
				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.
				.Ef
				.Pp
				DIMM temperature monitoring should be disabled before returning from
				.Fn imcsmb_pci_request_bus ,
				and re-enabled before returning from
				.Fn 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.
				.Po
				Unfortunately, those modifications were based on material covered under a
				non-disclosure agreement, and therefore are not included in this driver.
				.Pc
				The driver has also been tested and shown to work as-is on various motherboards
				from SuperMicro.
				.Pp
				The
				.Xr smb 4
				driver will connect to the
				.Xr smbus 4
				instances created by
				.Nm .
				However, since the IMC-SMBs are not general-purpose SMBus controllers, using
				.Xr smbmsg 8
				with those
				.Xr smb 4
				devices is not supported.
				.Sh SEE ALSO
				.Xr jedec_dimm 4 ,
				.Xr smbus 4
				.Sh HISTORY
				The
				.Nm
				driver first appeared in
				.Fx 12.0 .
				.Sh AUTHORS
				The
				.Nm
				driver was originally written for Panasas by
				.An Joe Kloss .
				It was substantially refactored, and this manual page was written, by
				.An Ravi Pokala Aq Mt rpokala@freebsd.org