I was interested in reading the RAM timing of my memory under Linux. Turns out this can be done with the decode-dimms command, which is part of the i2c-tools package.
To get this to work I had to do several steps though:
Reboot and add the following kernel parameter: acpi_enforce_resources=lax
By default this is set to strict, which meant that the i2c-i801 module was prevented from using the SMBUS controller. This could be seen from the following messages in dmesg:
[ 2.338436] ACPI Warning: SystemIO range 0x000000000000f000-0x000000000000f01f conflicts with OpRegion 0x000000000000f000-0x000000000000f00f (\_SB_.PCI0.SBUS.SMBI) (20140926/utaddress-258)
[ 2.338442] ACPI: If an ACPI driver is available for this device, you should use it instead of the native driver
[ 2.338471] i801_smbus 0000:00:1f.3: SMBus using PCI Interrupt
and looking at the lshw output, the SMBUS controller was unclaimed:
*-serial UNCLAIMED
description: SMBus
product: 7 Series/C210 Series Chipset Family SMBus Controller
vendor: Intel Corporation
physical id: 1f.3
bus info: pci@0000:00:1f.3
version: 04
width: 64 bits
clock: 33MHz
configuration: driver=i801_smbus latency=0
resources: irq:18 memory:f7f15000-f7f150ff ioport:f000(size=32)
After rebooting with the kernel parameter, an additional dmesg line will be outputted indicating the conflict has been allowed
[ 2.338436] ACPI Warning: SystemIO range 0x000000000000f000-0x000000000000f01f conflicts with OpRegion 0x000000000000f000-0x000000000000f00f (\_SB_.PCI0.SBUS.SMBI) (20140926/utaddress-258)
[ 2.338441] ACPI: This conflict may cause random problems and system instability
[ 2.338442] ACPI: If an ACPI driver is available for this device, you should use it instead of the native driver
[ 2.338471] i801_smbus 0000:00:1f.3: SMBus using PCI Interrupt
Finally, the eeprom module needs to be inserted:
modprobe eeprom
After that, decode-dimms should work as expected:
[root@orinoco ~]# decode-dimms
# decode-dimms version 6231 (2014-02-20 10:54:34 +0100)
Memory Serial Presence Detect Decoder
By Philip Edelbrock, Christian Zuckschwerdt, Burkart Lingner,
Jean Delvare, Trent Piepho and others
Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/0-0050
Guessing DIMM is in bank 1
---=== SPD EEPROM Information ===---
EEPROM CRC of bytes 0-116 OK (0xE8AC)
# of bytes written to SDRAM EEPROM 176
Total number of bytes in EEPROM 256
Fundamental Memory type DDR3 SDRAM
Module Type UDIMM
etc....