Hi Harry,

A kernel bug report was opened against Ubuntu [0].  After a kernel
bisect, it was found the following commit introduced the bug:


commit 4562236b3bc0a28aeb6ee93b2d8a849a4c4e1c7c
Author: Harry Wentland <[email protected]>
Date:   Tue Sep 12 15:58:20 2017 -0400

    drm/amd/dc: Add dc display driver (v2)


The regression was introduced as of v4.15-rc1 and still exists in
current mainline.  The commit does not need to be reverted to resolve
the bug.  Disabling the CONFIG_DRM_AMD_DC_PRE_VEGA option makes the bug
go away.
   
I was hoping to get your feedback, since you are the patch author.  Do
you think gathering any additional data will help diagnose this issue?
   

Thanks,

Joe


[0] http://pad.lv/1761751

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https://bugs.launchpad.net/bugs/1761751

Title:
  Black screen on 18.04 + AMD RX460

Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Bionic:
  In Progress

Bug description:
  I've been running 16.04 + hwe kernel 4.15 for a while now and recently
  I'm now having a black screen instead. I've also tried an 18.04 daily
  live USB stick, which has the same issue.

  It probably started during an upgrade this week or last week. As a
  start I'm blaming the Linux kernel since booting a 4.13 kernel works
  just fine.

  Known faulty kernel versions are:
   * linux-image-4.15.0-041500-generic (mainline kernel),
   * linux-image-4.16.0-041600-generic (mainline kernel),
   * linux-image-4.15.0-13-generic (Ubuntu kernel),
   * whatever comes with 18.04 daily live USB stick as of 20180404.

  Not sure how to best collect logs and system information for you since
  I'm not used to debugging black screens, so I'm just attaching lspci
  as a start.

  EDIT: Workaround found by adding "amdgpu.dc=0" to kernel boot
  parameters.

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