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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Dell TB16 external displays blank in kernel 4.14.4+"
href="https://bugs.freedesktop.org/show_bug.cgi?id=104425">104425</a>
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<th>Summary</th>
<td>Dell TB16 external displays blank in kernel 4.14.4+
</td>
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<th>Product</th>
<td>DRI
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>Other
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>DRM/Intel
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<th>Assignee</th>
<td>intel-gfx-bugs@lists.freedesktop.org
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<th>Reporter</th>
<td>arequipeno@gmail.com
</td>
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<th>QA Contact</th>
<td>intel-gfx-bugs@lists.freedesktop.org
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<th>CC</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
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<pre>Created <span class=""><a href="attachment.cgi?id=136464" name="attach_136464" title="dmesg from working kernel (commit 56350fb8978bbf4aafe08f21234e161dd128b417)">attachment 136464</a> <a href="attachment.cgi?id=136464&action=edit" title="dmesg from working kernel (commit 56350fb8978bbf4aafe08f21234e161dd128b417)">[details]</a></span>
dmesg from working kernel (commit 56350fb8978bbf4aafe08f21234e161dd128b417)
TL;DR - Commit a45b30a6c5db631e2ba680304bd5edd0cd1f9643 breaks external
displays attached to a Dell TB16 dock.
Hardware is a Dell Precision 5520 "developer edition" laptop attached to a Dell
TB16 (Thunderbolt 3) dock. This laptop does not have a separate discrete GPU,
only the GPU integrated into its Core i5 processor.
OS is Fedora 27, but dmesg files in this bug are from mainline kernel.
When the laptop is docked, it is closed, and I use *only* the displays (and
keyboard, etc.) attached to the TB16. This works fine up through commit
56350fb8978bbf4aafe08f21234e161dd128b417, but commit
a45b30a6c5db631e2ba680304bd5edd0cd1f9643 causes the displays to be disabled as
soon as the i915 module is loaded, leaving no working display at all.
I had a heck of a time preventing the i915 module from being loaded, so the two
dmesg files were produced with the following sequence:
* Blacklist the i915 module in /etc/modprobe.d and rebuild the initramfs
* Rename the i915.ko file under /lib/modules/...
* Reboot to multi-user.target
* Remove the drm modules that somehow got auto-loaded
- modprobe -r drm_kms_helper
- modprobe -r drm
* Rename i915.ko back to its correct file name
* Load the drm and i915 modules with debugging enabled
- modprobe drm debug=0x0f
- modprobe i915</pre>
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