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<b><a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [GLK DSI] Black screen after grub - Ubuntu 18.04 - kernel latest tip 21.11.2018"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108826#c128">Comment # 128</a>
on <a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [GLK DSI] Black screen after grub - Ubuntu 18.04 - kernel latest tip 21.11.2018"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108826">bug 108826</a>
from <span class="vcard"><a class="email" href="mailto:stanislav.lisovskiy@intel.com" title="Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>"> <span class="fn">Stanislav Lisovskiy</span></a>
</span></b>
<pre>(In reply to Mark Wynn Garcia from <a href="show_bug.cgi?id=108826#c126">comment #126</a>)
<span class="quote">> Stani. I think I know the problem. I'm still at work so I couldn't test it.
>
> I think it's because of the call to devm_gpiod_get_index() is only done
> once, with the first call's value.
>
> gpio_desc = devm_gpiod_get_index(dev_priv->drm.dev,
> NULL, gpio_index,
> value ? GPIOD_OUT_LOW : GPIOD_OUT_HIGH);
>
> The look at gpiod_set_value() -> gpiod_set_value_nocheck()
> (<a href="https://github.com/torvalds/linux/blob/master/drivers/gpio/gpiolib.c#L3335">https://github.com/torvalds/linux/blob/master/drivers/gpio/gpiolib.c#L3335</a>).
> It flips the value if it's flagged as low. See also gpiod_configure_flags().
> So if it happens that the initial call sets the GPIOD_OUT_LOW flag, then
> every subsequent calls will have the value flipped. So it can never set the
> GPIO to 1/true!</span >
This would probably make almost all panels unusable :) Also even for this
tablet backlight is working as expected..</pre>
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