Manual Pages  — JEDEC_DIMM

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

jedec_dimm_load="YES"

Addressing information must be manually specified in /boot/device.hints:

hint.jedec_dimm.0.at="smbus0"
hint.jedec_dimm.0.addr="0xa0"
hint.jedec_dimm.0.slotid="Silkscreen"

The jedec_dimm driver accesses the SPD and TSOD over the smbus(4).

The data is reported via a sysctl(8) interface; all values are read-only:

dev.jedec_dimm.X.%desc
	a string description of the DIMM, including TSOD and slotid info if present.
dev.jedec_dimm.X.capacity
	the DIMM's memory capacity, in megabytes
dev.jedec_dimm.X.part
	the manufacturer's part number of the DIMM
dev.jedec_dimm.X.serial
	the manufacturer's serial number of the DIMM
dev.jedec_dimm.X.slotid
	a copy of the corresponding hint, if set
dev.jedec_dimm.X.temp
	if a TSOD is present, the reported temperature
dev.jedec_dimm.X.type
	the DIMM type (DDR3 or DDR4)

These values are configurable for jedec_dimm via device.hints(5):

hint.jedec_dimm.X.at
	the smbus(4) to which the DIMM is connected
hint.jedec_dimm.X.addr
	the SMBus address of the SPD. JEDEC specifies that the four most-significant bits of the address are the "Device Type Identifier" (DTI), and that the DTI of the SPD is 0xa. Since the least-significant bit of an SMBus address is the read/write bit, and is always written as 0, that means the four least-significant bits of the address must be even.
hint.jedec_dimm.X.slotid
	optional slot identifier. If populated with the DIMM slot name silkscreened on the motherboard, this provides a mapping between the DIMM slot name and the DIMM serial number. That mapping is useful for detailed asset tracking, and makes it easier to physically locate a specific DIMM when doing a replacement. This is useful when assembling multiple identical systems, as might be done by a system vendor. The mapping between bus/address and DIMM slot must first be determined, either through motherboard documentation or trial-and-error.

If the DIMMs are on an I2C bus behind an iicbus(4) controller, then the iicsmb(4) bridge driver can be used to attach the smbus(4).

hint.jedec_dimm.0.at="smbus0"
hint.jedec_dimm.0.addr="0xa0"
hint.jedec_dimm.0.slotid="A1"

hint.jedec_dimm.6.at="smbus1"
hint.jedec_dimm.6.addr="0xa8"

Their sysctl(8) output (sorted):

dev.jedec_dimm.0.%desc: DDR4 DIMM w/ Atmel TSOD (A1)
dev.jedec_dimm.0.%driver: jedec_dimm
dev.jedec_dimm.0.%location: addr=0xa0
dev.jedec_dimm.0.%parent: smbus0
dev.jedec_dimm.0.%pnpinfo:
dev.jedec_dimm.0.capacity: 16384
dev.jedec_dimm.0.part: 36ASF2G72PZ-2G1A2
dev.jedec_dimm.0.serial: 0ea815de
dev.jedec_dimm.0.slotid: A1
dev.jedec_dimm.0.temp: 32.7C
dev.jedec_dimm.0.type: DDR4

dev.jedec_dimm.6.%desc: DDR4 DIMM w/ TSE2004av compliant TSOD
dev.jedec_dimm.6.%driver: jedec_dimm
dev.jedec_dimm.6.%location: addr=0xa8
dev.jedec_dimm.6.%parent: smbus1
dev.jedec_dimm.6.%pnpinfo:
dev.jedec_dimm.6.capacity: 8192
dev.jedec_dimm.6.part: VRA9MR8B2H1603
dev.jedec_dimm.6.serial: 0c4c46ad
dev.jedec_dimm.6.temp: 43.1C
dev.jedec_dimm.6.type: DDR4

The following sed(1) script will perform the necessary changes:

sed -i ".old" -e 's/jedec_ts/jedec_dimm/' \
    -e '/jedec_dimm/s/addr="0x3/addr="0xa/' /boot/device.hints