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<b><a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - i915.fastboot=1 is broken on Thinkpad S1 Yoga (Haswell)"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108773#c19">Comment # 19</a>
on <a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - i915.fastboot=1 is broken on Thinkpad S1 Yoga (Haswell)"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108773">bug 108773</a>
from <span class="vcard"><a class="email" href="mailto:ville.syrjala@linux.intel.com" title="Ville Syrjala <ville.syrjala@linux.intel.com>"> <span class="fn">Ville Syrjala</span></a>
</span></b>
<pre>(In reply to Johannes Krampf from <a href="show_bug.cgi?id=108773#c18">comment #18</a>)
<span class="quote">> Created <span class=""><a href="attachment.cgi?id=144329" name="attach_144329" title="Dmesg of drm-tip with fastboot on T440s">attachment 144329</a> <a href="attachment.cgi?id=144329&action=edit" title="Dmesg of drm-tip with fastboot on T440s">[details]</a></span>
> Dmesg of drm-tip with fastboot on T440s
>
> This is drm-tip version 307cedb7b907ee533bf9e746d0e06bea04f2722b from Thu
> May 23 12:49:55 2019 +1000. I used drm.debug=0xe on the kernel flags as
> requested. Previously I had 0x1e.
>
> The behaviour changed slightly with drm-tip:
>
> On startup, I still get the sub-second flash with boot messages and then the
> screen _including the backlight_ turns off. I can interact with the system
> (wayland+VT), but get no screen output.</span >
OK. I guess we're dealing with a backlight problem at this point.
We do see the telltale signs here:
[ 0.910355] [drm:lpt_setup_backlight] CPU backlight register was enabled,
switching to PCH override
The code was supposed to be fixed so that it can do the CPU->PCH switch but it
looks like it's still not working correctly.</pre>
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