Reading DDR4 SPD Information on Supermicro M11SDV

Viewing DIMM SDP data under Linux is usually a trivial affair. On my Framework (gen 11) laptop, this went something like this:

sudo apt install i2c-tools
sudo modprobe eeprom
sudo modprobe i2c-i801
sudo decode-dimms

However, on my Supermicro M11SDV server with AMD Epyc 3000 processor, this didn't work. No matter what I did, nothing would show. After messing around a bit, I found the solution on Unraid forum.

First, I needed to find where is SPD actually listening. The easiest way to determine this is to first list all I2C buses and then search for devices between I2C addresses 0x50 and 0x57:

sudo i2cdetect -l
sudo i2cdetect -y 0 0x50 0x57
sudo i2cdetect -y 1 0x50 0x57
sudo i2cdetect -y 2 0x50 0x57

For my motherboard, I actually found output on bus number 2. It looked something like this:

Warning: Can't use SMBus Quick Write command, will skip some addresses
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:
10:
20:
30:
40:
50: 50 51 52 53 -- -- -- --
60:
70:

Once the bus is found, we just need to load the ee1004 module that works on AMD board. This has to be repeated for each I2C address that was found. Do note that the path contains the I2C bus number (in my case i2c-2).

sudo modprobe ee1004
echo ee1004 0x50 | sudo tee /sys/bus/i2c/devices/i2c-2/new_device
echo ee1004 0x51 | sudo tee /sys/bus/i2c/devices/i2c-2/new_device
echo ee1004 0x52 | sudo tee /sys/bus/i2c/devices/i2c-2/new_device
echo ee1004 0x53 | sudo tee /sys/bus/i2c/devices/i2c-2/new_device

And now finally we can run decode-dimms again and read all that lovely SPD data.