linux-kernel - [BUG] "Pre-boot DMA Protection" makes AMDGPU stop working

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Message-Id: <546DB0FA-FDEB-4FD1-93CD-AA5474B5F0DD@canonical.com>
Date:   Thu, 2 Jul 2020 20:04:20 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     "Deucher, Alexander" <alexander.deucher@....com>,
        iommu@...ts.linux-foundation.org,
        open list <linux-kernel@...r.kernel.org>
Subject: [BUG] "Pre-boot DMA Protection" makes AMDGPU stop working

Hi,

A more detailed bug report can be found at [1].

I have a AMD Renoir system that can't enter graphical session because there are many IOMMU splat.

Alex suggested to disable "Pre-boot DMA Protection", I can confirm once it's disabled, AMDGPU starts working with IOMMU enabled.
So raise the issue here because I have no knowledge on how to reset the IOMMU.

[1] https://gitlab.freedesktop.org/drm/amd/-/issues/1204

Kai-Heng