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SMBus Access

Source: https://gitlab.com/CalcProgrammer1/OpenRGB/-/raw/master/Documentation/SMBusAccess.md

SMBus (System Management Bus) is a low-level interface present on most PC motherboards, commonly used to connect RGB lighting devices. This includes DDR4/DDR5 RAM modules with integrated RGB and onboard lighting on motherboards from the X370/Z270 and X470/Z370 generations. While SMBus is typically restricted from user applications, RGB control software like OpenRGB requires special access.

i2c kernel modules

  1. Install the i2c-tools package.
  2. Load the i2c-dev module: sudo modprobe i2c-dev
  3. Load the i2c driver for your chipset:
    • Intel: sudo modprobe i2c-i801
    • AMD: sudo modprobe i2c-piix4
    • Nuvoton
      • This interface is used alongside i2c-i801 on some older ASUS Intel motherboards for the on-board lighting.
      • sudo modprobe i2c-nct6793
      • Note: The i2c-nct6793 driver must be installed separately, see i2c-nct6793-dkms

  • If you want the i2c modules to load automatically at boot, run the following:

    1. sudo touch /etc/modules-load.d/i2c.conf
    2. sudo sh -c 'echo "i2c-dev" >> /etc/modules-load.d/i2c.conf'
    3. Run the following based on which i2c drivers you loaded in the previous section:
      • sudo sh -c 'echo "i2c-i801" >> /etc/modules-load.d/i2c.conf'
      • sudo sh -c 'echo "i2c-piix4" >> /etc/modules-load.d/i2c.conf'

  • You will have to enable user access to the i2c devices if you don’t run OpenRGB as root.

    1. List all SMBus controllers: sudo i2cdetect -l
    2. Note the number(s) for piix4 or i801 controllers.
    3. Give user access to those controllers. If you have not installed OpenRGB from a distribution package then most likely you need to install the udev rules manually.

Gigabyte/Aorus motherboard special case

Some Gigabyte/Aorus motherboards have an ACPI conflict with the SMBus controller. You can bypass this conflict by adding the acpi_enforce_resources=lax kernel parameter to your kernel command line. See the Arch Wiki Kernel Parameters page for more information.

spd5118 driver conflict

The spd5118 kernel driver can claim certain I2C addresses for Kingston Fury DDR5 memory and thus prevent other kernel modules from accessing them. This is the case if the i2cdetect command prints the character string UU on the I2C bus responsible for the DRAM. A solution to this problem is to unload the spd5118 kernel driver using rmmod spd5118.