[Bug 196117] New: amdgpu RC 480 (polaris) freeze after initramfs, before kernel load

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=196117

            Bug ID: 196117
           Summary: amdgpu RC 480 (polaris) freeze after initramfs, before
                    kernel load
           Product: Drivers
           Version: 2.5
    Kernel Version: 4.11.6
          Hardware: x86-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri at kernel-bugs.osdl.org
          Reporter: paulkgerke at craftware.nl
        Regression: No

Created attachment 257069
  --> https://bugzilla.kernel.org/attachment.cgi?id=257069&action=edit
screen capture of the last kernel messages before system freeze

Hey all!

I recently swapped out my old Radeon HD7850 for a Radeon RX 480, that I only
heard good things about on the Internet because of good kernel support.
However, I ran into an issue: all kernels I tried hang after initramfs, but
before the kernel actually boots. Here the symptoms:

I tried several kernels by now, the stock kernels that come with XUbuntu 16.04,
and several upstream ones (e.g. 4.12.0). This will be about 4.11.6, which I now
compiled myself.

- If I use "nomodeset" to boot the kernel, everything works fine, except for
the graphics drivers which fails to initialize (amdgpu fails because of VGACON
error).

- If I boot in with options
    "linux /vmlinuz... root=UUID=xxxx ro debug ignore_loglevel boot_delay=100"

    PS: I also setup a serial link for debugging, but the crash seems to occur
before the serial driver can start communicating, so no luck with that!

- I see "loading initial ramdisk..." ... booting takes 3 minutes until the
crash with that delay...
  - I taped the whole thing to at least capture some sort of error. The
attached screenshot is the best I got at the moment.

It says something about IOMMUv2 driver and... about it being not "avaialble on
the system" (?) Is that my error? This is the last (half) frame before my
screen turns black.

After this, my keyboard LEDs turn off, my mouse also turns off (it has fancy
LEDs which light up if it is initialized) and my screen stays **on**,
curiously. The machine is not responding after this.

At the moment I am stuck lacking good debugging tools. If somebody has an idea,
I would be greatful. Until now, the only thing I can think of is digging into a
fresh codebase - I bet graphics drivers are not really accessible though :-(

One last PS: The graphicscard I have works perfectly fine on Windows on the
same system. It is clearly some software issue, I assume!

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