Dell U2412M Unable to Switch Back From Source 3 to 15

[pranavanmaru]

Pre-Conditions:

1. Dell U2412M is Display 2
2. Display 2 Connected via Display Port (15) to a Macbook Pro
3. Display 2 Connected via DVI Port (3) to a PC
4. Display 2 Currently Active on Mac (via 15).

Reproduction Steps:

1. Run ddcctl -d 2 -i 3 on Mac to Switch Display 2 over to DVI Port.
   • Monitor switches input source as expected.
2. Run ddcctl -d 2 -i 15 on Mac to Switch Display 2 back over to Display Port.
   • Expected: Monitor switches input source to display port
   • Actual: No change observed. Monitor remained active with DVI Port (Input Source 3)

Logs

ddcctl -d 2 -i 3
D: CGDisplay FD7794D8-FEB4-3C97-894E-A41FAD6C76FE dispID(#722484499) (2560x1440 0°) HiDPI
D: CGDisplay D039A244-01A3-A446-3225-76AF1E2F22F9 dispID(#724061848) (1920x1200 0°) 94.00 DPI
I: found 2 external displays
I: polling EDID for #2 (ID 724061848 => IOService:/AppleACPIPlatformExpert/PCI0@0/AppleACPIPCI/PEG0@1/IOPP/GFX0@0/ATY,Longavi@2/AMDFramebufferVIB)
I: got edid.serial: 7WFG151G0BPS
I: got edid.name: DELL U2412M
D: action: i: 3
D: setting VCP control #96 => 3

[itxch]

What is the output when running ddcctl -d 2 -i 15
Also, try ddcctl -d 2 -i 16

[kfix]

I think the Input Values that were contributed to the README are more what you'd call guidelines than actual rules.
Seconding @itxchh 's suggestion to try some other numbers (but at your own risk).
Welcome to ddcctl 🏴‍☠️!