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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 - Unexpected screen flicker during i915 initialization"
href="https://bugs.freedesktop.org/show_bug.cgi?id=112178">112178</a>
</td>
</tr>
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<th>Summary</th>
<td>Unexpected screen flicker during i915 initialization
</td>
</tr>
<tr>
<th>Product</th>
<td>DRI
</td>
</tr>
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<th>Version</th>
<td>XOrg git
</td>
</tr>
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<th>Hardware</th>
<td>x86-64 (AMD64)
</td>
</tr>
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<th>OS</th>
<td>Linux (All)
</td>
</tr>
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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>not set
</td>
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<th>Component</th>
<td>DRM/Intel
</td>
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<th>Assignee</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
</tr>
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<th>Reporter</th>
<td>chiu@endlessm.com
</td>
</tr>
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<th>QA Contact</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
</tr>
<tr>
<th>CC</th>
<td>intel-gfx-bugs@lists.freedesktop.org
</td>
</tr></table>
<p>
<div>
<pre>We have 2 laptops, ASUS Z406MA and Acer TravelMate B118, both powered by the
same Intel N5000 GemniLake CPU. On the Acer laptop, the panel will blink once
during boot which never happens on the ASUS laptop. It caught my attention and
I find the difference between them but I need help for more information,
The major difference happens in bxt_sanitize_cdclk() on the following
condition check.
if (cdctl == expected)
/* All well; nothing to sanitize */
return;
On the problematic Acer laptop, the value of cdctl is 0x27a while the same
cdctl is 0x278 on ASUS machine. Due to the 0x27a is not equal to the expected
value 0x278 so it needs to be sanitized by assigning -1 to
dev_priv->cdclk.hw.vco. Then the consequent bxt_set_cdclk() will force the full
PLL disable and enable. And that's the flicker (blink) we observed during boot.
Although I can't find the definition of the BIT(2) of CDCLK_CTL which
causes this difference. I reproduced this bug on latest 5.3 mainline and also
kernel built from <a href="https://github.com/freedesktop/drm-intel">https://github.com/freedesktop/drm-intel</a>. But I think it's
not really about i915 driver if the content from register CDCLK_CTL is
unexpected. Can anyone suggest what exactly the problem is and how should we
deal with it? Thanks.
Please ref. <a href="https://lkml.org/lkml/2019/10/30/240">https://lkml.org/lkml/2019/10/30/240</a> mail thread here.</pre>
</div>
</p>
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