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<th>Priority</th>
<td>medium
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [Intel GM45] xrandr --output <output> --mode <prev_mode> is not able to light up an output that has been disabled with xrandr --off."
href="https://bugs.freedesktop.org/show_bug.cgi?id=64178">64178</a>
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<th>Assignee</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
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<th>Summary</th>
<td>[Intel GM45] xrandr --output <output> --mode <prev_mode> is not able to light up an output that has been disabled with xrandr --off.
</td>
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<th>QA Contact</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Classification</th>
<td>Unclassified
</td>
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<th>OS</th>
<td>Linux (All)
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<th>Reporter</th>
<td>eich@pdx.freedesktop.org
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<th>Hardware</th>
<td>x86-64 (AMD64)
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<th>Status</th>
<td>NEW
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<th>Version</th>
<td>unspecified
</td>
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<th>Component</th>
<td>DRM/Intel
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<th>Product</th>
<td>DRI
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=78802" name="attach_78802" title="Proposed Fix.">attachment 78802</a> <a href="attachment.cgi?id=78802&action=edit" title="Proposed Fix.">[details]</a></span>
Proposed Fix.
This issue has been found on a Intel GM45 (0x8086 0x2a42) (among others):
1. Start an Xserver on a system with multiple outputs attached.
2. Ensure all outputs are lit.
3. Disable one output with 'xrandr --output <output_ID> --off
4. Observe this output become blank and enter power saving state.
5. Issue xrandr --output <output_ID> --mode <previous_mode>
=> One will observe that this output will remain blank.
Investigation results:
The problem is an asymetric behavior in intel_crtc_set_config(): If a full mode
set is required any encoders in power save state are activated as a side
effect. Otherwise they are simply left in their provious state.
This asymetry in behavior can cause a surprising and unexpected behavior.
The attached patch will fix this problem. There are possibly other ways to fix
the issue - to me this seemed to be the simplest.
Ticket opened to put the patch up for discussion.</pre>
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