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<body><span class="vcard"><a class="email" href="mailto:lakshminarayana.vudum@intel.com" title="Lakshmi <lakshminarayana.vudum@intel.com>"> <span class="fn">Lakshmi</span></a>
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<a class="bz_bug_link
bz_status_NEW "
title="NEW - Brightness control inversion from VBT table is not taken into account in Ubuntu 18.10"
href="https://bugs.freedesktop.org/show_bug.cgi?id=111475">bug 111475</a>
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<th>What</th>
<th>Removed</th>
<th>Added</th>
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<td style="text-align:right;">CC</td>
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<td>jani.nikula@intel.com
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<td style="text-align:right;">Status</td>
<td>NEEDINFO
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<td>NEW
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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Brightness control inversion from VBT table is not taken into account in Ubuntu 18.10"
href="https://bugs.freedesktop.org/show_bug.cgi?id=111475#c7">Comment # 7</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Brightness control inversion from VBT table is not taken into account in Ubuntu 18.10"
href="https://bugs.freedesktop.org/show_bug.cgi?id=111475">bug 111475</a>
from <span class="vcard"><a class="email" href="mailto:lakshminarayana.vudum@intel.com" title="Lakshmi <lakshminarayana.vudum@intel.com>"> <span class="fn">Lakshmi</span></a>
</span></b>
<pre>(In reply to Szymon from <a href="show_bug.cgi?id=111475#c4">comment #4</a>)
<span class="quote">> I'm not sure what do you exactly mean by "BIOS enable the display". For sure
> LVDS display is switched on and I can see the screen. I assume BIOS enabled
> it.
>
> I provided requested files as attachments.
>
> Can you point Intel's document number which describes the content of
> register which should be set by BIOS?
>
> P.S. I'm running Ubuntu from USB stick (without installation).</span >
(In reply to Szymon from <a href="show_bug.cgi?id=111475#c5">comment #5</a>)
<span class="quote">> Today I performed another tests a here are the results:
>
> 1. Confirmed that Linux does not take VBT backlight active low bit into
> consideration. If this is the bug that is to be decided by Linux graphic
> driver developers. NOTE: Windows graphic driver takes this setting into
> consideration.
>
> 2. Once BIOS writes 0xC8250 MMIO register with bit 29, backlight logic is
> inverted correctly. However 10% minimum brightness level defined in VBT
> table is NOT taken into account in this case, i.e. Linux brightness slider
> set at maximum produces complete darkness instead of 10% brightness (as set
> as minimum).
>
> 3. In comparison to point 2: Once backlight logic is inverted by kernel boot
> parameter acpi_backlight=vendor i915.invert_brightness=1, slider at max
> still respects minimum brightness level 10% defined in VBT.</span >
Jani, any further comments?</pre>
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