Display Data Channel DDCUtil stopped detecting both monitors after 470.57.02 update

Graphics / Linux Linux
1

I just updated to 470.57.02 from the OpenSUSE Tumbleweed repo. Prior to the update (and reboot) I was successfully using ddcutil to change the brightness of my two monitors, but now ddcutil detect only reports one of them:

% ddcutil detect  
Display 1
   I2C bus:             /dev/i2c-8
   EDID synopsis:
      Mfg id:           GSM
      Model:            LG HDR 4K
      Serial number:    
      Manufacture year: 2019
      EDID version:     1.4
   VCP version:         2.1

Ddutil used to display two monitors, “DDC-Display” 1 used to be an HP ZR24w (DVI->HDMI cable connected), and DDC-Display 2 was my LG HDR 4K (displayport cable), but now ddutil only reports my LG display as DDC-Display 1. The only change was an update to the nvidia driver and a reboot (twice to check the problem would shake loose). In other respects the two monitors are working normally.

Is this a known issue for 470.57.02?

2

I found some old notes I had made, they had not been applied to this system:

- Nvidia enable i2c
    - Needed for ddcutil - not really of any use at this point, but included for reference
    - xorg.conf
        Section "Device"
            Identifier     "Device0"
            Driver         "nvidia"
            Option         "RegistryDwords"  "RMUseSwI2c=0x01; RMI2cSpeed=100"
            VendorName     "NVIDIA Corporation"
            BoardName      "GeForce GTX 1650 SUPER"
        EndSection
    - /etc/modprobe.d/99-local.conf and run ldconfig afterwards:
        options nvidia NVreg_RegistryDwords=RMUseSwI2c=0x01;RMI2cSpeed=100

I applied them and now ddcutil reports both monitors:

ddcutil detect                                                                                                                 ✔  10001  18:11:42
Display 1
   I2C bus:             /dev/i2c-5
   EDID synopsis:
      Mfg id:           HWP
      Model:            HP ZR24w
      Serial number:    XXXXXXXXX
      Manufacture year: 2010
      EDID version:     1.3
   VCP version:         2.2

Display 2
   I2C bus:             /dev/i2c-8
   EDID synopsis:
      Mfg id:           GSM
      Model:            LG HDR 4K
      Serial number:    
      Manufacture year: 2019
      EDID version:     1.4
   VCP version:         2.1

For some reason, prior to kernel 5.13.2-1-default, nvidia and ddcutil was working without these config entries.

I actually rebooted to 5.13.1-1 to check and yes ddutil works without these settings (although the boot with the new 470 driver does actually make it to sddm).

Everything’s back to what it should be now.