[Bug 90776] New: hdmi audio: spec violation for >=uhd-4k TMDS clock frequencies, no audio out in worst case

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90776

            Bug ID: 90776
           Summary: hdmi audio: spec violation for >=uhd-4k TMDS clock
                    frequencies, no audio out in worst case
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: critical
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: joe.konno at linux.intel.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

It is believed that Intel GPUs which support uhd-4k/3840x2160 resolutions over
HDMI are not setting N/CTS values correctly during audio(-over-hdmi) playback.
This can result in no audio being played back over the display's speakers.

The HDMI >=1.4 spec specifies audio sampling rate, TMDS clock frequencies, and
N/CTS values for uhd-4k displays. The N/CTS values are not being supported for
the TMDS clock frequencies associated with uhd-4k displays.

In the i915 display code there needs to be a mechanism for kernel audio drivers
(e.g. HDA) to signal the display driver when the audio sampling rate changes,
which will trigger a lookup within the display driver to ensure correct N/CTS
values are set.

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