This seems to be the answer to my issues. The card is an RX550 so it shouldn't need that line but it does. What exactly am I losing by using it? I know it affects audio through hdmi/display port but I don't need that anyway.

TL;DR: With amdgpu.dc=0, my 1440p monitor works, but intensive games will eventually crash my system. With amdgpu.dc=1, intensive games are perfectly stable, but my 1440p monitor doesn't work.

I'll start from the beginning.

When I upgraded to Lubuntu 18.04 w/ Kernel 4.15 back in April my primary monitor, a 1440p DVI monitor, was receiving no signal. Xrandr could detect the monitor was plugged in, but no modes were found. After some Googling I found out that setting amdgpu.dc=0 fixed this problem.

Fast forward to Wednesday and with the recent release of Steam Play, I'm eager to start testing some games. I launch a number of titles and run a few benchmarks, everything seems fine. Then I try to play GTA V for an extended period of time. This is when I discover that after playing for about 30 minutes, the graphics start to get corrupted and then eventually my system freezes.

I look at my kernel log and discover that at the exact moment the graphical corruption begins, I start getting spammed with variations of the following lines:

Aug 25 23:54:59 THE-GIANT-SLAB kernel: [10462.962860] amdgpu 0000:23:00.0: GPU fault detected: 146 0x0ff0480c
Aug 25 23:54:59 THE-GIANT-SLAB kernel: [10462.962864] amdgpu 0000:23:00.0:   VM_CONTEXT1_PROTECTION_FAULT_ADDR   0x000003FE
Aug 25 23:54:59 THE-GIANT-SLAB kernel: [10462.962866] amdgpu 0000:23:00.0:   VM_CONTEXT1_PROTECTION_FAULT_STATUS 0x0404800C
Aug 25 23:54:59 THE-GIANT-SLAB kernel: [10462.962869] amdgpu 0000:23:00.0: VM fault (0x0c, vmid 2) at page 1022, read from 'TC4' (0x54433400) (72)

I spend a couple of days running various tests to try and either verify or debunk the claim of a faulty GPU. I had a breakthrough today when I decided to try launching the kernel without amdgpu.dc=0. As expected, it boots up and my 1440p monitor is not receiving a signal. I have now been playing GTA V for about two hours without any errors in dmesg.

So that's the situation. I can either have my monitor working, and experience full system crashes, or I can have perfectly stable gameplay, but only on my smaller secondary monitor. As I'm sure you can imagine, neither situation is particularly ideal.

How do I even start trying to come up with a solution to this?

Thanks in advance for your advice.

EDIT: Dunno how I completely forgot to post my specs. Derp.

GPU: 8GB Sapphire RX 480 Nitro+

CPU: AMD Ryzen 5 1600

RAM: 16GB Corsair Vengeance LPX 3200MHz

Mobo: MSI Tomahawk B350

Kernel: 4.15.0.33-generic

Mesa version: 18.3.0-devel (padoka PPA)

EDIT 2: Installing a fresher kernel sorted it out. Currently using my 1440p monitor with AMDGPU DC enabled. Thanks everyone! Now if you'll excuse me, I'm off to play some GTA V...

My linux mint computer is not booting. It wouldn't boot on normal mode either when I was trying the live usb installer(I had to use compatibility mode). I added amdgpu.dc=0 by pressing TAB. My question is how can I edit the boot cfg before linux mint starts. I know that in fedora you have to press E, but on linux mint?