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<base href="https://bugs.freedesktop.org/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Corrupted video output with 32bit kernel"
href="https://bugs.freedesktop.org/show_bug.cgi?id=91831">91831</a>
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<th>Summary</th>
<td>Corrupted video output with 32bit kernel
</td>
</tr>
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<th>Product</th>
<td>xorg
</td>
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<th>Version</th>
<td>git
</td>
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<th>Hardware</th>
<td>x86 (IA32)
</td>
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<th>OS</th>
<td>Linux (All)
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>Driver/AMDgpu
</td>
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<th>Assignee</th>
<td>xorg-driver-ati@lists.x.org
</td>
</tr>
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<th>Reporter</th>
<td>nholland@tisys.org
</td>
</tr>
<tr>
<th>QA Contact</th>
<td>xorg-team@lists.x.org
</td>
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<p>
<div>
<pre>I'm not entirely sure if this is the right place to mention this issue, but I'm
fairly confident that the right people will see it here:
I'm using a Kabini GPU on a 32-bit (kernel + userland) system using linux 4.2
and have just decided to give the amdgpu kernel drm driver and
xf86-video-amdgpu a try (previously I was using radeon). What I noticed is that
screen output in X11 is garbled using these drivers - i.e. pixels are messed up
/ missing / corrupt in various places all over the screen.
I've seen this issue before in the radeon driver, there's actually a (resolved)
bug report about it at <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - (bisected) 32bit corruption with PIPE_USAGE_STREAM reverted"
href="show_bug.cgi?id=84627">https://bugs.freedesktop.org/show_bug.cgi?id=84627</a>.
Back then, the bug was fixed in the kernel in
linux/drivers/gpu/drm/radeon/radeon_object.c. Here's the relevant section (from
radeon_bo_create()):
#ifdef CONFIG_X86_32
/* XXX: Write-combined CPU mappings of GTT seem broken on 32-bit
* See <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - (bisected) 32bit corruption with PIPE_USAGE_STREAM reverted"
href="show_bug.cgi?id=84627">https://bugs.freedesktop.org/show_bug.cgi?id=84627</a>
*/
bo->flags &= ~RADEON_GEM_GTT_WC;
I'm not into this stuff enough, but I believe that in contrast to the radeon
driver, the amdgpu driver does not disable write-combined CPU mappings on 32
bit kernels. The question is: Would it be possible and reasonable to change
amdgpu to follow radeon in this regard and thus - hopefully - fix the garbled
screen problem on 32 bit?
As a side note, the problem goes away when disabling hardware acceleration:
Option "NoAccel" "true"
Screen output looks good then. Still, this is probably not the best solution.</pre>
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