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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - [CHV] Backlight init fails on Surface 3 if module load order is wrong"
href="https://bugs.freedesktop.org/show_bug.cgi?id=96571#c10">Comment # 10</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - [CHV] Backlight init fails on Surface 3 if module load order is wrong"
href="https://bugs.freedesktop.org/show_bug.cgi?id=96571">bug 96571</a>
from <span class="vcard"><a class="email" href="mailto:viric@viric.name" title="viric@viric.name">viric@viric.name</a>
</span></b>
<pre>I guess that the pwm driver patches are OK, as they were in this my LPSS:
<a href="http://www.spinics.net/lists/intel-gfx/msg92110.html">http://www.spinics.net/lists/intel-gfx/msg92110.html</a>
But the problem is that there is no glue between any PWM and i915 other than
drivers/video/backlight/pwm_bl.c. It only adds support for *some* PWM devices
to be used as backlight, and only in CONFIG_OF (embedded x86, with devicetree,
non-ACPI).
So, PWM works, i915 works, but the pwm-backlight glue called by i915 is not
present in x86 ACPI.
<a href="http://lxr.free-electrons.com/source/drivers/video/backlight/pwm_bl.c#L195">http://lxr.free-electrons.com/source/drivers/video/backlight/pwm_bl.c#L195</a>
See how pwm_backlight_probe() calls just pwm_backlight_parse_dt(), that for
non-CONFIG_OF just returns -ENODEV. Then, i915 never finds a backlight pwm for
an ACPI (non-CONFIG_OF) system).</pre>
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