H370M-ITX/ac black screen over Display Port

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   Issue:
No post logo, no video until the GPU driver is loaded.
Sometimes in a blink of an eye I can see the ASRock bios logo but it returns black until the OS loads the GPU driver.
I happens only when the display is connected via Display Port cable. HDMI works fine with CSM disabled.

I prefer Display Port to get FreeSync support.

My config: 
ASRock H370M-ITX/ac (Bios v3.0), 
Intel i5-8400
MSI Vega 56 AirBoost OC
Samsung ultra wide 3550x1440 @100Hz
OS X 10.14.3
The built-in UHD 630 iGPU is enabled in bios but no display is connected.

I tried:
- to set the display to DP1.1 instead of DP1.4
- two different Mini Display cables, one is VGA certified
- change the display?�s ultra wide setting from auto to Ultra wide
- upgrade to bios v3.1
- downgraded to bios v3.0 
- closed the Cmos jumper on the MLB without the power cable.

I found another thread for the same issue on z370 fatality itx.

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mushmuch Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 02 Apr 2019 Status: Offline Points: 6	Post Options Post Reply Quote mushmuch Report Post Thanks(0) Quote Reply Topic: H370M-ITX/ac black screen over Display Port Posted: 02 Apr 2019 at 1:42am
	Issue: No post logo, no video until the GPU driver is loaded. Sometimes in a blink of an eye I can see the ASRock bios logo but it returns black until the OS loads the GPU driver. I happens only when the display is connected via Display Port cable. HDMI works fine with CSM disabled. I prefer Display Port to get FreeSync support. My config: ASRock H370M-ITX/ac (Bios v3.0), Intel i5-8400 MSI Vega 56 AirBoost OC Samsung ultra wide 3550x1440 @100Hz OS X 10.14.3 The built-in UHD 630 iGPU is enabled in bios but no display is connected. I tried: - to set the display to DP1.1 instead of DP1.4 - two different Mini Display cables, one is VGA certified - change the display?�s ultra wide setting from auto to Ultra wide - upgrade to bios v3.1 - downgraded to bios v3.0 - closed the Cmos jumper on the MLB without the power cable. I found another thread for the same issue on z370 fatality itx.

mushmuch Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 02 Apr 2019 Status: Offline Points: 6	Post Options Post Reply Quote mushmuch Report Post Thanks(0) Quote Reply Posted: 02 Apr 2019 at 1:51am
	Edit: The issue happens only with CSM disabled over Display Port. I tried 2 different certified DP cables The DP cables work fine after OS has loaded the GPU driver.

ASRock_TSD Members Profile Send Private Message Find Members Posts Add to Buddy List ASRock_Official Joined: 20 Mar 2015 Status: Offline Points: 8907	Post Options Post Reply Quote ASRock_TSD Report Post Thanks(0) Quote Reply Posted: 02 Apr 2019 at 10:02am
	Dear Mushmuch, Thank you for choosing ASRock. Regarding your case, we provide some suggestion to try. 1. Change another DP monitor to try. 2. Remove the graphics card and use the onboard DP to try. Thank you! Yours truly, ASRock TSD

mushmuch Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 02 Apr 2019 Status: Offline Points: 6	Post Options Post Reply Quote mushmuch Report Post Thanks(0) Quote Reply Posted: 03 Apr 2019 at 4:38am
	Hi, So I removed the GPU and I can access the Bios with DP port cable when connected directly to the MLB. I don't have another display to test. I updated bios to v4.0 which does not resolve the GPU + DP+ CSM_off issue. It flickers a bit more so I can see the OS loading bar intermittently. BUT now I have another problem, the OS won't boot with Bios v4.0 and I get an invalid file error when trying to flash the 3.0 bios from USB... Please help me downgrade back to Bios v3, my computer is a brick now :'(

mushmuch Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 02 Apr 2019 Status: Offline Points: 6	Post Options Post Reply Quote mushmuch Report Post Thanks(0) Quote Reply Posted: 05 Apr 2019 at 4:57pm
	I found a workaround: turn on the picture in picture mode in the monitor settings. This reduces the frame to 17220x1440 which is working for the bios and GPU.