[Bug 80455] New: Missing Start of Audio Stream with Samsung S24C650PL HDMI monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=80455

          Priority: medium
            Bug ID: 80455
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: Missing Start of Audio Stream with Samsung S24C650PL
                    HDMI monitor
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: mengdong.lin at intel.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: XOrg CVS
         Component: DRM/Intel
           Product: DRI

The first ~500ms of HDMI audio stream are not played, if we play another stream
within 5 seconds, the beggining is correctly played.

This issue has been observed only with Samsung S24C650PL monitor, with and
without X launched, with monitor built-in speakers or headset, on HSW, BYT-M
and BDW. There is the data missing problem with Display Port only the first
playback, unlike HDMI where it is reproduced each time. RTD3 is disabled. 
During the process, no mode set happens for the HDMI monitor (1920x1080 at 60.0,
transcoder B, port C) and the video display is good. 

Reproduced with mainline kernels v3.14.0 and v3.15-rc1

We have checked the BDW gfx audio registers but found nothing wrong. 
So we dumped the video registers by intel_reg_dumper, and need gfx team's help
to check if gfx side is also okay:
(1)     IRD_hdmi_only.txt   … register dump before we play the audio stream
over HDMI
(2)     IRD_hdmi_only_play.txt  … register dump when we’re playing the audio
stream over HDMI

I only found RC6_RESIDENCY_TIME increases. The dmesg is also attached.

Atm, we suspect the audio receiver part of this monitor can easily sleep and
need some time to wake up and synchronize new audio stream, so there is audible
audio frame loss.

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