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<body><span class="vcard"><a class="email" href="mailto:eich@pdx.freedesktop.org" title="Egbert Eich <eich@pdx.freedesktop.org>"> <span class="fn">Egbert Eich</span></a>
</span> changed
<a class="bz_bug_link
bz_status_ASSIGNED "
title="ASSIGNED --- - [snb pch eDP regression] Screen sometimes remains black after mode change - old fast & narrow link is more stable"
href="https://bugs.freedesktop.org/show_bug.cgi?id=65757">bug 65757</a>
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<th>What</th>
<th>Removed</th>
<th>Added</th>
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<td style="text-align:right;">Status</td>
<td>NEEDINFO
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<td>ASSIGNED
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<b><a class="bz_bug_link
bz_status_ASSIGNED "
title="ASSIGNED --- - [snb pch eDP regression] Screen sometimes remains black after mode change - old fast & narrow link is more stable"
href="https://bugs.freedesktop.org/show_bug.cgi?id=65757#c7">Comment # 7</a>
on <a class="bz_bug_link
bz_status_ASSIGNED "
title="ASSIGNED --- - [snb pch eDP regression] Screen sometimes remains black after mode change - old fast & narrow link is more stable"
href="https://bugs.freedesktop.org/show_bug.cgi?id=65757">bug 65757</a>
from <span class="vcard"><a class="email" href="mailto:eich@pdx.freedesktop.org" title="Egbert Eich <eich@pdx.freedesktop.org>"> <span class="fn">Egbert Eich</span></a>
</span></b>
<pre>Thanks to Michal Srb, who took the task to perform this tedious investigation
we came to the following conclusions:
1. Of the eDP specific code paths we only need ironlake_edp_panel_on/off()
and the call to intel_dp_init_panel_power_sequencer_registers() in
intel_dp_init_connector() to make the panel work properly every time.
2. Some WARN() messages are triggered as the VDD enable/disable functions
are not called. This however is harmless as the VDD doesn't seem to be
controlled by the GPU as it seems (the panel works although the
EDP_FORCE_VDD is off all the time).
3. Only enabling ironlake_edp_panel_off() will result in a dark screen
all the time. This allows the conclusion that the panel power is controlled
by the GPU.
If none of the ironlake_edp_panel_on/off() functions are called (as it is in
the DP case) the panel power remains on all the time (preset by the BIOS).
For some reason the panel needs to undergo a power sequence during mode switch
(ie when the DP lanes get retrained). Why this only needs to happen when two
lanes are active is not really clear - it may have to do with a brief loss of
the panel LVDS signaling which may case the panel to blank.
To me there are two conclusions possible:
a. the device should really be treated DEVICE_TYPE_eDP in the eDP BDB of VBT.
or
b. a fix is required for a device outside of the control of the driver (ie. the
Chrontel CH7511B (e)DP -> LVDS converter).</pre>
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