`ddcutil capabilities` on a Framework 16 with F42 returns "display not found", even with `sudo` prepended.

[RokeJulianLockhart]

An Example

RokeJulianLockhart@Beedell:~$ sudo ddcutil capabilities
Display not found

My Environment

• ddcutil

  • Per https://github.com/rockowitz/ddcutil/issues/241#issuecomment-3190208735, the output of sudo ddcutil interrogate --verbose is available at gist.github.com/RokeJulianLockhart/dfc2ab90d8fcdbbb0f5d4351e2e32ed2.

  • 1. #!/usr/bin/env bash
       dnf5 info $(rpm -qa ddcutil)
       

    2. Name            : ddcutil
       Epoch           : 0
       Version         : 2.1.4
       Release         : 2.fc42
       Architecture    : x86_64
       Installed size  : 1.1 MiB
       Source          : ddcutil-2.1.4-2.fc42.src.rpm
       From repository : <unknown>
       URL             : http://www.ddcutil.com
       Vendor          : Fedora Project
       
       

• Hardware

  1. #!/usr/bin/env bash
     hwinfo --monitor
     

  2. 46: None 00.0: 10002 LCD Monitor                                
       [Created at monitor.125]
       Unique ID: rdCR.HLVCnEUYHWA
       Parent ID: 0Gk3.6FldxGZRsU8
       Hardware Class: monitor
       Model: "BOE CQ LCD Monitor"
       Vendor: BOE "BOE CQ"
       Device: eisa 0x0bc9 
       Serial ID: "0"
       Resolution: 2560x1600@60Hz
       Size: 345x215 mm
       Year of Manufacture: 2022
       Week of Manufacture: 48
       Detailed Timings #0:
          Resolution: 2560x1600
          Horizontal: 2560 2608 2640 2720 (+48 +80 +160) -hsync
            Vertical: 1600 1663 1669 1760 (+63 +69 +160) +vsync
         Frequencies: 287.24 MHz, 105.60 kHz, 60.00 Hz
       Config Status: cfg=new, avail=yes, need=no, active=unknown
       Attached to: #21 (VGA compatible controller)
     

[rockowitz]

The bottom line: Laptop displays do not support DDC/CI.

The ddcutil detect command, whose output is included in the interrogate output, reports "This is a laptop display. Laptop displays do not support DDC/CI".

The capabilities command is meaningful only for displays that support DDC/CI. No such display exists on your system. Hence the message "Display not found".

[RokeJulianLockhart]

@rockowitz, do you believe that this message can be improved? Considering that KDE Plasma somehow manages to modify the display's brightness, I was under the impression that ddcutil was how it (presumably, PowerDevil) accomplished this.

[rockowitz]

Laptop display brightness is controlled using ACPI, not DDC/CI. Powerdevil uses ACPI, not ddcutil, for laptop displays.

Following the practice of Argyll CMS, displays supporting DDC/CI are numbered from 1. The display number is reported by the detect command. If no explicit display selection option (e.g. --display, --bus, --model, --sn, --edid) is specified on a command that operates on a valid display, option --display 1 is assumed. But there is no display found that matches that selection criterion. Hence the message "Display not found".

[RokeJulianLockhart]

@rockowitz, so do you think that the message should be improved? If not, I'll close as unplanned. However, I imagine that this'll appear again in the future when another user is confused. Thanks for the explanation.