I have a Lenovo T420s with displayport and discrete graphics chip (NVidia GF119).  I installed CentOS 7 with pulseaudio and all works great - for a while.  Then audio stops.pavucontrol shows the GF119 connected to my monitor, and the graphical slider in pavucontrol moves with the audio being sent...but no sound is heard.  I have to power cycle the laptop to restore audio to the displayport again.On startup the syslog shows:[    3.357359] input: HDA NVidia HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input14[    3.357429] input: HDA NVidia HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input15[    3.357486] input: HDA NVidia HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input16[   14.475665] snd_hda_codec_hdmi hdaudioC1D0: HDMI: invalid ELD data byte 8[   14.487664] snd_hda_codec_hdmi hdaudioC1D0: HDMI: invalid ELD data byte 0but there are no HDMI related message after bootup.I'm not sure how begin to diagnose this...is it pulseaudio issue? displayport? Nvidia? CentOS?  I tried using 'speaker-test' with every device and internal laptop speakers work, but no sounds from the monitor connected by displayport.Can someone offer steps to track down the cause?  (I found a similar issue enter link description here but not sure if relevant)UPDATE: After the problem appeared I killed pulseaudio and ran speaker-test direct to my 3 HDMI devices, and no audio heard.  So I assume not a pulseaudio issue.  I tried to compare pre- and post-failure of various sound settings, and noticed that proc/sound/card0/codec0 my stream=0 changes to stream=5 in case that means anything??Node 0x08 [Audio Output] wcaps 0x62b1: 8-Channels Digital Stripe  Converter: stream=5, channel=0  Digital: Enabled GenLevel  Digital category: 0x2  IEC Coding Type: 0x0  PCM:    rates [0x7f0]: 32000 44100 48000 88200 96000 176400 192000    bits [0xe]: 16 20 24    formats [0x5]: PCM AC3  Unsolicited: tag=00, enabled=0
Display losing audio, need power cycle to restore
centos;nvidia;pulseaudio;displayport