[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 #114 from Stanislav Lisovskiy <stanislav.lisovskiy at intel.com> ---
There seem to be some issue with gpio pins used in vbt sequences used for
Microtech Etab. 
I see that backlight gpio pin index 4 works as supposed, while accessing others
actually breaks the display. That explains also why initially it did work
without
geminilake_pinctrl - it simply couldn't access those, which was visible in the
log.

I confirmed this also by adding small hack to mipi_exec_gpio function so that
it doesn't touch pins 3, 6 which used for power_on and reset respectively. 
Then my etab works with geminilake_pinctrl, also I can see the backlight
switching on/off during suspend/resume. However display still stays blank. To
me it looks like either there is something wrong with the vbt sequence or those
pins are misconfigured somehow.

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