[Bug 1761751] Re: Black screen on 18.04 + AMD RX460

Just as an update, in the Freedesktop issue, I found using a LOWER
specced/older cable to fix the problem.

I do not know how to debug it further but I suspect the bug is in the
support of later version of the HDMI standard.

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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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