Failed to find connector name error with modified EDID

[Gray-Rice]

Hi,
I am trying to get a modified version of EDID of my monitor to work with ddcutil. I2c works and I am able to use command line functions like setvcp and getvsp, but due to the 'Failed to find connector name' error applications like the kde plasma brightness control fail.

I use drm.edid_firmware=HDMI-A-1:edid/edid_fast.bin kernel parameter to load edid.

ddcutil interrogate outputs:

stock: ddcutil_stock.txt
modified: ddcutil_modified.txt

ddcutil detect --verbose output:

 ddcutil detect --verbose
Failed to find connector name for /dev/i2c-3, set_connector_for_businfo_using_edid at line 1411 in file i2c_bus_core.c. 
Display 1
   I2C bus:  /dev/i2c-3
      Driver:                                    nvidia
      I2C address 0x30 (EDID block#)  present:   false
      EDID exists:                               true
      I2C address 0x37 (DDC) responsive:         true
      Is LVDS or EDP display:                    false
      Is laptop display by EDID:                 false
      Is laptop display:                         false
      /sys/bus/i2c/devices/i2c-3/name            NVIDIA i2c adapter 3 at 1:00.0
      PCI device path:                           /sys/devices/pci0000:00/0000:00:01.1/0000:01:00.0/i2c-3
   EDID synopsis:
      Mfg id:               DEL - Dell Inc.
      Model:                DELL U2417H
      Product code:         16616  (0x40e8)
      Serial number:        9F8JF91ACNML
      Binary serial number: 1129205068 (0x434e4d4c)
      Manufacture year:     2019,  Week: 2
      EDID version:         1.3
      Extra descriptor:        
      Video input definition:    0x80 - Digital Input
      Supported features:
         DPMS standby
         DPMS suspend
         DPMS active-off
         Digital display type: RGB 4:4:4 + YCrCb 4:4:4
         Standard sRGB color space: False
      White x,y:        0.313, 0.329
      Red   x,y:        0.640, 0.330
      Green x,y:        0.300, 0.600
      Blue  x,y:        0.150, 0.060
      Extension blocks: 1
   EDID source: I2C
   EDID hex dump:
        +0          +4          +8          +c            0   4   8   c   
+0000   00 ff ff ff ff ff ff 00 10 ac e8 40 4c 4d 4e 43   ...........@LMNC
+0010   02 1d 01 03 80 35 1e 78 ea ee 95 a3 54 4c 99 26   .....5.x....TL.&
+0020   0f 50 54 a5 4b 00 71 4f 81 80 a9 40 d1 c0 01 01   .PT.K.qO...@....
+0030   01 01 01 01 01 01 02 3a 80 18 71 38 2d 40 58 2c   .......:..q8-@X,
+0040   45 00 0f 28 21 00 00 1e 00 00 00 ff 00 39 46 38   E..(!........9F8
+0050   4a 46 39 31 41 43 4e 4d 4c 0a 00 00 00 fc 00 44   JF91ACNML......D
+0060   45 4c 4c 20 55 32 34 31 37 48 0a 20 00 00 00 fd   ELL U2417H. ....
+0070   00 32 4b 1e 53 11 00 0a 20 20 20 20 20 20 01 4e   .2K.S...      .N
   VCP version:         2.1
   Controller mfg:      Mstar
   Firmware version:    65.5
   Monitor correctly uses invalid feature flag in DDC reply packet to indicate unsupported feature.
   Current dynamic sleep adjustment multiplier:  0.00
   Monitor Model Id:  DEL-DELL_U2417H-16616
   Feature definition file DEL-DELL_U2417H-16616.mccs not found.

[rockowitz]

The problem is that for detecting display connection/disconnection, libddcutil needs to associate the monitor's sysfs card-connector directory with the I2C bus number. Recent open source drivers puts a connector number in the the card-connector directory that can be used to make the association. The Nvidia proprietary driver does not, so the edid attribute in the card-connector directory is used to make the association. Those EDIDs are out of sync. More precisely, in ddcutil_stock.txt command ddcutil detect show the same EDID as that in card1-HDMI-A-1/edid (the final byte is x4E). In ddcutil_modified.txt, command detect shows the same EDID, but card1-A-1/edid is different (final byte is xAA).

Offhand, I don't have a simple solution for your problem. You can try using the following options (solo or in combination) to see if they address it:

• --disable-watch-displays. libddcutil does not watch for display connection/disconnection
• ---disable-try-get-edid-from-sysfs
• --f22. This utility option currently causes sysfs to be regarded as unreliable.

If they don't, implementing a solution to your problem would be a significant enhancement.

[Gray-Rice]

Thank you for your reply,
unfortunately the options dont seem to change anything, also Kinfocenter has EDID reporting which shows correct connector,
Is there any specific change i can do to the EDID to fix this or is it a more of a driver issue ?

[rockowitz]

The only thing you could do would be to be actually install the EDID in the monitor. Your override is happening at the drm level, whereas ddcutil in this situation gets the EDID directly from the monitor by reading it from /dev/i2c. Conceivably there could be an option to explicitly connect a /dev/i2c device with a sysfs drm card connector directory, but then ddcutil would have 2 different EDIDs for the same monitor, and that would have to be untangled.

[Gray-Rice]

My monitor has a write protected EEPROM , so unfortunately writing EDID is a hassle.
If nothing else we can close this issue.

[rockowitz]

Branch 2.2.8-dev contains a change intended to address your issue. Option --bus-drm-connector allows you to explicitly set the bus number/connection name in situations where ddcutil cannot figure this out. For example --bus-drm-connector 5 card1-DP-1.

Let me know if this solves your problem.

[programminghoch10]

Hello,
wanted to chime in on this issue regarding the surrounding issue of KDE Powerdevil integration.
Currently on latest stable ddcutil on Arch Linux (not your mentioned branch) I experience the same issue:

journalctl log

(I have 4 displays all with EDID override enabled)

systemd[1215]: Starting Powerdevil...
org_kde_powerdevil[887619]: Starting libddcutil. library built Not set at Not set. stdout_stderr_redirected=true
org_kde_powerdevil[887619]: Starting. library built Not set at Not set, library_initialized=false, libopts=|(null)|
org_kde_powerdevil[887619]: Initializing libddcutil.  ddcutil version: 2.2.7, shared library: /usr/lib/libddcutil.so.5.5.1
org_kde_powerdevil[887619]:                           library built Not set at Not set. stdout_stderr_redirected=true
org_kde_powerdevil[887619]: [887619] Options passed from client:
org_kde_powerdevil[887619]: [887619] Applying combined libddcutil options:
org_kde_powerdevil[887619]: (ddci_init                     ) Calling ldbus_start_sleep_watch_thread...
org_kde_powerdevil[887619]: [887619][  0.048171] (ldbus_pause_if_recent_return_from_sleep)Pausing for 483
org_kde_powerdevil[887619]: [887619][  0.531269] paused for 483 millisec at start of i2c_open_bus_basic()
org_kde_powerdevil[887619]: Failed to find connector name for /dev/i2c-11, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: [887619] Failed to find connector name for /dev/i2c-11, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: Failed to find connector name for /dev/i2c-13, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: [887619] Failed to find connector name for /dev/i2c-13, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: Failed to find connector name for /dev/i2c-14, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: [887619] Failed to find connector name for /dev/i2c-14, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: Failed to find connector name for /dev/i2c-15, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: [887619] Failed to find connector name for /dev/i2c-15, set_connector_for_businfo_using_edid at line 1737 in file i2c_bus_core.c.
org_kde_powerdevil[887619]: [887676] (check_supported_feature) busno=11, sleep-multiplier =  2,00. Testing for supported feature 0x10 returned Error_Info[EIO in ddc_write_read_with_retry, causes: EIO]
org_kde_powerdevil[887619]: Library initialization complete.
org_kde_powerdevil[887619]: [887619][  1.873831] (ddci_init) Done.  Returning 0
org_kde_powerdevil[887619]: [887619] Starting ddca_start_watch_displays()
org_kde_powerdevil[887619]: Watching for DPMS state changes unimplemented
org_kde_powerdevil[887619]: [887619] Watching for DPMS state changes unimplemented
org_kde_powerdevil[887619]: [887619][  1.875112] Time since library initialized:   1.875111 seconds
org_kde_powerdevil[887619]: [887619][  1.875114] Extra delay starting dw_start_watch_displays: 0 millisec
org_kde_powerdevil[887619]: [887619] Watching for display connection changes, resolved watch mode = Watch_Mode_Udev, poll loop interval = 500 millisec
org_kde_powerdevil[887619]: [887619]                                          initial_stabilization_millisec: 0,  stabilization_poll_millisec: 100
org_kde_powerdevil[887619]: [887619] libddcutil recheck thread 0x5597edf33aa0 started
org_kde_powerdevil[887619]: [887619] libddcutil watch thread 0x5597edf4bda0 started
org_kde_powerdevil[887619]: [887619] Done     ddca_start_watch_displays returning OK - OK(0): success
org_kde_powerdevil[887619]: [887690][  1.887018] Recheck interval: Sleeping for 200 milliseconds
org_kde_powerdevil[887619]: [887619][  1.887020] (ddca_get_display_refs) Returned DDCA_Display_Ref list:
org_kde_powerdevil[887619]: [887619][  1.887039]    DDCA_Display_Ref Display_Ref[2:bus /dev/i2c-13 @0x5597edf2d870]
org_kde_powerdevil[887619]: [887619][  1.887042]    DDCA_Display_Ref Display_Ref[3:bus /dev/i2c-14 @0x5597edf2ed40]
org_kde_powerdevil[887619]: [887619][  1.887044]    DDCA_Display_Ref Display_Ref[4:bus /dev/i2c-15 @0x5597edf32a80]
systemd[1]: Started dbus-:1.3-org.kde.powerdevil.discretegpuhelper@1.service.
systemd[1]: Started dbus-:1.3-org.kde.powerdevil.chargethresholdhelper@1.service.
systemd[1]: Started dbus-:1.3-org.kde.powerdevil.backlighthelper@1.service.
backlighthelper[887722]: no kernel backlight interface found
org_kde_powerdevil[887619]: Failed to register with host portal QDBusError("org.freedesktop.portal.Error.Failed", "Could not register app ID: App info not found for 'org.kde.org_kde_powerdevil'")
org_kde_powerdevil[887619]: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
org_kde_powerdevil[887619]: org.kde.powerdevil.backlighthelper.brightness failed
org_kde_powerdevil[887619]: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
systemd[1215]: Started Powerdevil.

Would the new option --bus-drm-connector need to be implemented and used on Powerdevil side,
or could this be fixed inside ddcutil?

In my case the ddcutil detect command shows the same "Failed to find connector name ..." errors as powerdevil does.

[rockowitz]

Option --bus-drm-connector should be included in the [global] section of your ddcutilrc configuration file so that it applies to both command line ddcutil and shared library libddcutil. There is nothing to be done on the powerdevil side.

[Gray-Rice]

Hello,
I have trouble using the new --bus-drm-connector i get the following errors.

$ ddcutil detect --bus-drm-connector "3 card1-HDMI-A-1"
(main                          ) Initialization errors:
(main                          )    --bus-drm-connector: invalid DRM connector name "card1-HDMI-A-1" (from "3 card1-HDMI-A-1")

But the DRM connector is correct.

Could you please guide me on how to use the command and config too.

[Gray-Rice]

Found Issue with the is_valid_drm_connector_name() it has the size of fq_name set to 20 , while the connector is longer and gets truncated.
I tested temporarily with the size increased, the issue still exists:

$ ddcutil detect --bus-drm-connector "/dev/i2c-3 card1-HDMI-A-1"
Failed to find connector name for /dev/i2c-3, set_connector_for_businfo_using_edid at line 1784 in file i2c_bus_core.c. 
Display 1
   I2C bus:  /dev/i2c-3
   EDID synopsis:
      Mfg id:               DEL - Dell Inc.
      Model:                DELL U2417H
      Product code:         16616  (0x40e8)
      Serial number:        9F8JF91ACNML
      Binary serial number: 1129205068 (0x434e4d4c)
      Manufacture year:     2019,  Week: 2
   VCP version:         2.1