[Bug 103786] New: DP audio does not work with Thinkpad Ultra Dock and DP-to-HDMI converter

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103786

            Bug ID: 103786
           Summary: DP audio does not work with Thinkpad Ultra Dock and
                    DP-to-HDMI converter
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: jan at 3e8.eu
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 135529
  --> https://bugs.freedesktop.org/attachment.cgi?id=135529&action=edit
dmesg: Dock DP connector with converter

I'm using a T460 with the Thinkpad Ultra Dock (contains Synaptics DP MST hub)
and  a DP-HDMI converter (CAC-1070, based on PS176) to connect a 4K TV.

In this configuration the DP audio output is detected, but no audio can
actually be heard. When connecting directly via HDMI or using the converter on
the internal DP port of the laptop, audio works fine.

I have attached the dmesg output with drm.debug=0xe for the following test
cases:

Dock DP connector with converter -> no audio
Internal DP connector with converter -> audio works
Dock HDMI connector -> audio works
Internal HDMI connector -> audio works

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