Created attachment 143625 [details]
Non working audio with Samsung 4K Series D model

Connecting Samsung Monitor 4K display(U28D590) to Chromebook (WHL), audio doesn't route to display (same device and monitor works fine with HDMI ). Connection type is USB Type-C to DP. Audio drivers are legacy HD Audio and graphics is i915. 

Issue only happens with this particular monitor U28D590 and not happening on Samsung 4K U28E590, Dell or any other monitor(as far as I know).
 
I have also read edid after connection and it shows "Audio Data Block"
evtest is also passes.

Issue is not reprodcible after adding 5 sec delay: 

diff --git a/drivers/gpu/drm/i915/intel_audio.c b/drivers/gpu/drm/i915/intel_audio.c
index ee3ca2de983b..9c794968bb2a 100644
--- a/drivers/gpu/drm/i915/intel_audio.c
+++ b/drivers/gpu/drm/i915/intel_audio.c
@@ -26,7 +26,7 @@
#include <drm/i915_component.h>
#include <drm/intel_lpe_audio.h>
#include "intel_drv.h"
-
+#include<linux/delay.h>
#include <drm/drmP.h>
#include <drm/drm_edid.h>
#include "i915_drv.h"
@@ -456,7 +456,8 @@ static void hsw_audio_codec_enable(struct intel_encoder *encoder,
        const u8 *eld = connector->eld;
        u32 tmp;
        int len, i;
-
+       mdelay(5000);
        DRM_DEBUG_KMS("Enable audio codec on pipe %c, %u bytes ELD\n",
                      pipe_name(pipe), drm_eld_size(eld));

Important Observations:
1. Same monitor U28D590 works fine on Windows or any other chromebook.
2. Tried on different platforms with Legacy –HDA (no dsp), issue is reproducible
3. If above mentioned delay is less than 5 sec, issue is reproducible.
4. Issue reproducible with drm-tip; 78b288a16a32 drm-tip: 2019y-03m-08d-19h-11m-52s UTC integration manifest