Created attachment 144799 [details]
logs with stock fedora kernel and drm-tip

The device with the following problem is a IGEL UD2-LX50 (internal M250C) with 2 DisplayPorts (yes one is the eDP used as normal DP but both are affected).

To Reproduce:

    * connect a 2560x1440 capable monitor (some 4k also have the same problem) like DELL P2715Q, ACER S277HK, ASUS MX27UQ, iiyama ProLite PL2792Q, Fujitsu p27-8TS Pro.... on the DP connector

    * start the system

    * the monitor will get black after pulseaudio was started (on Ubuntu after the login screen, on Fedora directly)

If pulseaudio is disabled (very quick and dirty with "sudo mv /usr/bin/pulseaudio /usr/bin/pulseaudio.real; sudo ln -sf /bin/true /usr/bin/pulseaudio") it works with the stock Fedora Kernel and with the Ubuntu default kernel. With drm-tip the screen goes directly black short after boot.

Logfiles were created with drm.debug=0x3ff kernel commandline option.

The stock-fedora-30-pulsaudio-disabled.log file shows a boot with disabled pulseaudio and working Screen with Fedora 30. In Gnome a Console was opened and pulsaudio.real started and the screen went black nearly immediately. One can grep for the pulseaudio.real start message to get in the area the error happened.

With drm-tip the error occurs with or without running pulseaudio, there were also two logfiles created. drm-tip-kernel-without-fix.log is the drm-tip from 2019-07-16 and there the screen is black shortly after boot (blinking cursor and then black). As I know how to workaround this issue I did a small change in the drm-tip kernel:

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 0eb5d66f87a7..3aed538e24c2 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -5322,7 +5322,8 @@ intel_dp_set_edid(struct intel_dp *intel_dp)
 	edid = intel_dp_get_edid(intel_dp);
 	intel_connector->detect_edid = edid;
 
-	intel_dp->has_audio = drm_detect_monitor_audio(edid);
+	//intel_dp->has_audio = drm_detect_monitor_audio(edid);
+	intel_dp->has_audio = false;
 	drm_dp_cec_set_edid(&intel_dp->aux, edid);
 }

This only prevents the usage of DP audio, then the screen is working as one would expect (drm-tip-kernel-with-fix.log logfile).

Our own Linux is based on Ubuntu (Kernel is a 4.19.x mainline one with some fixes) and there the issue is also present, also with a Stock Ubuntu with Linux mainline or Ubuntu Kernel. We currently worked around it with a added i915 module parameter to disable DP audio support (Kernel Patch) but this is not a solution only a workaround.

If one need a device to test he could contact me and I will look if I can arrange this.