DDC communication failed over USB-C Dock

[criemen]

Hi,

I tried using ddcutil in the following setup: Thinkpad T14s laptop with AMD Ryzen processor+GPU external monitor connected to the Lenovo USB-C Gen 2 dock via DisplayPort.

However, I get the following output

sudo ddcutil detect
Invalid display
   I2C bus:             /dev/i2c-5
   EDID synopsis:
      Mfg id:           AUO
      Model:
      Serial number:
      Manufacture year: 2018
      EDID version:     1.4
   DDC communication failed
   This is an eDP laptop display. Laptop displays do not support DDC/CI.

Invalid display
   I2C bus:             /dev/i2c-6
   EDID synopsis:
      Mfg id:           DEL
      Model:            DELL U2713HM
      Serial number:    PRIVATE
      Manufacture year: 2012
      EDID version:     1.4
   DDC communication failed

Is there anything I can provide to help debug the issue?

I did run modprobe i2c-dev, and I'm running ddcutil using sudo to alleviate the permission problems. I am using ddcutil 0.9.9 from the arch linux repositories.

Edit: DDC is enabled in the OSD

[rockowitz]

Have you tried connecting without the dock, using  HDMI?

Please send the output of "sudo ddcutil interrogate" as an attachment.

On 10/5/20 6:40 PM, Cornelius Riemenschneider wrote:

Hi,

I tried using ddcutil in the following setup: Thinkpad T14s laptop with AMD Ryzen processor+GPU external monitor connected to the Lenovo USB-C Gen 2 dock via DisplayPort.

However, I get the following output

|sudo ddcutil detect Invalid display I2C bus: /dev/i2c-5 EDID synopsis: Mfg id: AUO Model: Serial number: Manufacture year: 2018 EDID version: 1.4 DDC communication failed This is an eDP laptop display. Laptop displays do not support DDC/CI. Invalid display I2C bus: /dev/i2c-6 EDID synopsis: Mfg id: DEL Model: DELL U2713HM Serial number: PRIVATE Manufacture year: 2012 EDID version: 1.4 DDC communication failed |

Is there anything I can provide to help debug the issue?

I did run modprobe i2c-dev, and I'm running ddcutil using sudo to alleviate the permission problems. I am using ddcutil 0.9.9 from the arch linux repositories.

— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/rockowitz/ddcutil/issues/146, or unsubscribe https://github.com/notifications/unsubscribe-auth/ADMGY3TL6U7YV6OVQB5PO7TSJJDNNANCNFSM4SFIPMKA.

[criemen]

Attaching the monitor via HDMI directly to the computer works. However, the monitor is useless connected via HDMI, because the native resolution (2k) of the monitor is not supported via HDMI.

I attached the output of ddcutil interrogate both with HDMI (working) and displayport over dock (not working).

ddcutil-interrogate-hdmi.txt ddcutil-interrogate-displayport-dock.txt

[rockowitz]

i2c failure on recent docking stations (i.e. using DisplayPort MST) is a well known problem.   See the bug report https://gitlab.freedesktop.org/drm/intel/-/issues/37 that I submitted 3 years ago. If you scroll to the end, you'll see that a driver fix was recently submitted.  It's in the drm driver, so hopefully it fixes the problem for amdgpu as well as i2c.   The fix may be in the 5.8 kernel, it certainly will be in 5.9.

In the meantime, you might try connecting a USB Type-C connector on the laptop to the DisplayPort connector on the monitor.

On 10/7/20 6:17 AM, Cornelius Riemenschneider wrote:

Attaching the monitor via HDMI directly to the computer works. However, the monitor is useless connected via HDMI, because the native resolution (2k) of the monitor is not supported via HDMI.

I attached the output of ddcutil interrogate both with HDMI (working) and displayport over dock (not working).

ddcutil-interrogate-hdmi.txt https://github.com/rockowitz/ddcutil/files/5339777/ddcutil-interrogate-hdmi.txt ddcutil-interrogate-displayport-dock.txt https://github.com/rockowitz/ddcutil/files/5339778/ddcutil-interrogate-displayport-dock.txt

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/rockowitz/ddcutil/issues/146#issuecomment-704839568, or unsubscribe https://github.com/notifications/unsubscribe-auth/ADMGY3RW4BKEV6EEVZDY52TSJQ52JANCNFSM4SFIPMKA.

[criemen]

5.8.14 does not help, but I expect 5.9 to land somewhat soon, and I'll report back. Unfortunately I don't have a USB-C to DP cable to test that case.

Thanks for the support!

[frogmaster]

Using 5.9.1 on arch and Dell WD19TB thunderbolt dock. The issue is unfortunately still not resolved. I've attached the interrogation log. ddc_interrogate.txt

[rockowitz]

Commit adb48b26985686f93f20ca71c16c067d790e7af3 (drm/dp_mst: Support remote i2c writes) is not in kernel release 5.9.1.

More specifically, it is not currently in

• branch linux-5.9.y at git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git

The commit is found in:

• branch master at git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
• branch master at https://github.com/torvalds/linux.git

[frogmaster]

Thanks for the clarification. Installed the linux-git arch package. Can confirm that, at least for my use case, ddcutil works great with tb dock and intel graphics.

[rockowitz]

The changes to file drm_dp_mst_topology.c are in just released kernel branch 5.10.

[ChrisAJS]

I'll hopefully be able to echo frogmaster's success- also experiencing an issue with the exact same Dock, (Dell WD19TB), so when I get the latest kernel I'll report whether or not it fixes my issue also. Freaking amazing tool!

[whirm]

Quick line to confirm it works just fine with my WD15TB dock! Thanks for this great tool!