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<base href="https://bugs.freedesktop.org/" />
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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 --- - turning off LVDS leads to acpi_video0/brightness:0 on another console"
href="https://bugs.freedesktop.org/show_bug.cgi?id=67025">67025</a>
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<th>Assignee</th>
<td>chris@chris-wilson.co.uk
</td>
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<th>Summary</th>
<td>turning off LVDS leads to acpi_video0/brightness:0 on another console
</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>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
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<th>OS</th>
<td>Linux (All)
</td>
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<th>Reporter</th>
<td>consume.noise@gmail.com
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<th>Hardware</th>
<td>x86-64 (AMD64)
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<th>Status</th>
<td>NEW
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Component</th>
<td>Driver/intel
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<th>Product</th>
<td>xorg
</td>
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<p>
<div>
<pre>First, I thought this was a kernel bug:
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - Vectors and hats are not correctly displayed"
href="show_bug.cgi?id=60545">Bug 60545</a> - acpi_video0/brightness:0 after VT switch
<a href="https://bugzilla.kernel.org/show_bug.cgi?id=60545">https://bugzilla.kernel.org/show_bug.cgi?id=60545</a>
"I'm having an X server configured to use the external monitor only (LVDS off).
If I switch from that X server to a console (or to another X server which uses
the LVDS), then the brightness of the LVDS stays at very low level (text is
unreadable)."
Now, I've figured out that xf86-video-intel is causing this behaviour. (The
affected code in uxa seems to be equal, but I've tested sna only.)
Commenting out the call to sna_output_dpms_backlight() when dpms==DPMSModeOff
in sna_output_dpms() fixed it.
What happens when disabling the LVDS output - the dpms state changes:
- sna_output_dpms(..., dpms=DPMSModeOff)
o sna_output_dpms_backlight(..., mode=DPMSModeOff)
* sna_output_backlight_set(..., 0)
-> writes 0 to $backlight_iface/brightness
o drmModeConnectorSetProperty(..., dpms=DPMSModeOff)
... from libdrm into the kernel ...
* intel_crtc_dpms()
-> disable encoder driving the LVDS connector
So, from what I think sna_output_backlight_set(..., 0) is not necessary as this
lowers the brightness, when the output gets turned off anyways. Maybe calling
sna_output_backlight_set() in the case of dpms!=DPMSModeOff is not necessary
too.
I've tested the patched version (just commenting out the dpms==DPMSModeOff case
in sna_output_dpms()) without the acpi_backlight kernel parameter (acpi_video)
and with acpi_backlight=vendor (thinkpad_screen). Both worked.
But, I'm not sure about the implications on other backlight interfaces, maybe
it's necessary for others or for older kernels. That's why I haven't made it a
patch yet.</pre>
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