[Bug 102069] New: Acer XB270HU I2C and EDID not working on iGPU + radeon/amdgpu

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102069

            Bug ID: 102069
           Summary: Acer XB270HU I2C and EDID not working on iGPU +
                    radeon/amdgpu
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: gerben at daybyday.nl
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 133284
  --> https://bugs.freedesktop.org/attachment.cgi?id=133284&action=edit
ddcutil on intel

I have a desktop with a Samsung SA850HD and an Acer XB270HU, both connected
with DP. The Acer screen does not return any EDID and reports I2C nack when
plugged in, both on the intel iGPU as well as on a HD7850 card. The Samsung
screen works great. It also doesn't matter if I plug in just the Acer, it
happens in single and multimonitor mode (for amdgpu/radeon).

What's more, the Acer screen works perfectly fine when plugged into a GTX980
with Nouveau driver (on another box booted with Ubuntu 17.04 live cd). So the
screen itself is fine. It also reports all valid data with softMCCS in Windows;
full DDC control is available there.

This is on 4.12.5 x86_64, Debian sid. Relevant smoking gun on intel:

     [   74.733494] [drm:intel_dp_start_link_train] Clock recovery check
failed, cannot continue channel equalization
      [   74.737037] [drm:drm_dp_i2c_do_msg] I2C nack (result=0, size=0

I've attached logs generated with ddcutil for each card which will show
summarized system info; I will attach full drm.debug=0xe dmesg shortly, please
advise if more info is needed.

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