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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - [LPT SPT KBP] Acer V3-772G screen brightness cannot be adjusted with i915.fastboot enabled"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108225#c26">Comment # 26</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - [LPT SPT KBP] Acer V3-772G screen brightness cannot be adjusted with i915.fastboot enabled"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108225">bug 108225</a>
from <span class="vcard"><a class="email" href="mailto:cevelnet@gmail.com" title="Tolga Cakir <cevelnet@gmail.com>"> <span class="fn">Tolga Cakir</span></a>
</span></b>
<pre>(In reply to Jani Nikula from <a href="show_bug.cgi?id=108225#c22">comment #22</a>)
<span class="quote">> Do you have LynxPoint (LPT) PCH? Look for something like this in the dmesg:
>
> [ 5.224781] [drm:intel_pch_type [i915]] Found LynxPoint PCH
>
> Does the trick from <a href="show_bug.cgi?id=108225#c12">comment #12</a> help? What's the output of the intel_reg
> reads in the two scenarios? (See <a href="show_bug.cgi?id=108225#c13">comment #13</a> for example.)</span >
My platform is Lynx Point (Intel HM87 chipset, Intel Core i7-4702HQ),
eventhough I don't see that specific line. I've done the tests on an Arch Linux
system, kernel 4.19.2.
After running the mentioned xrandr commands, my screen turns off for a second,
comes back on and backlight control works again. My output intel_reg read
output:
Fresh boot w/ fastboot (non-working backlight control):
BLC_PWM_PCH_CTL1 (0x000c8250): 0x80000000 (enable 1, override 0, inverted
polarity 0)
(0x000c2004): 0x00000004
BLC_PWM_PCH_CTL2 (0x000c8254): 0x131203b1 (freq 4882, cycle 945)
(0x00061250): 0x00000000
(0x00061254): 0x00000000
After running xrandr command (backlight control working):
BLC_PWM_PCH_CTL1 (0x000c8250): 0xc0000000 (enable 1, override 1, inverted
polarity 0)
(0x000c2004): 0x00000004
BLC_PWM_PCH_CTL2 (0x000c8254): 0x131203b1 (freq 4882, cycle 945)
(0x00061250): 0x00000000
(0x00061254): 0x00000000
@Maarten Lankhorst: Thanks for the patches in <a href="show_bug.cgi?id=108225#c23">comment #23</a> #24 #25! I'm setting
up a testing environment and will report back asap.</pre>
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