[Bug 108826] [GLK DSI] Black screen after grub - Ubuntu 18.04 - kernel latest tip 21.11.2018

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108826

--- Comment #128 from Stanislav Lisovskiy <stanislav.lisovskiy at intel.com> ---
(In reply to Mark Wynn Garcia from comment #126)
> 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()
> (https://github.com/torvalds/linux/blob/master/drivers/gpio/gpiolib.c#L3335).
> 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!

This would probably make almost all panels unusable :) Also even for this
tablet backlight is working as expected..

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