[DC] HDMI Monitor has Overscan/Scaling

Submitted by djb..@..rth.ca

Assigned to Default DRI bug account

Link to original bug (#106040)

Description

Created attachment 138831
Overscan issue on HP w2207h

With my HP w2207h monitor connected over HDMI, the image appears overscanned, it is cut off at the sides and is upscaled (see attached image, note how the top bar is missing with dc=1). It is possible to fit the image inside the monitor with xset --set underscan on and xset --set "underscan {hborder,vborder}", but this results in a blurry display.

This occurs with a RX Vega 64 and an RX 560 with amd-staging-drm-next commit 6d15a288b18119428b3af5d7a7641745e9f82860 (the latest at the time of testing) as well as mainline 4.16.0. With the RX 560, the overscanning only occurs when the new DC code is used, using the old code (with amdgpu.dc=0) results in a perfect display. This also doesn't affect any other monitor I own using HDMI.

Attached further are logs made with amdgpu.dc_log=1 and drm.debug=0x6 on the Vega 64, the 560 with amdgpu.dc=1, and the 560 with amdgpu.dc=0.

Attachment 138831, "Overscan issue on HP w2207h":