[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 #145 from Mark Wynn Garcia <markwynngarcia at outlook.com> ---
Hello Stanislav. I have some questions and observations with regards to
pinctrl/gpio.

Based on
https://github.com/torvalds/linux/blob/28e8c4bc8eb483c22d977e147a0b98fc63efadf7/drivers/pinctrl/intel/pinctrl-geminilake.c
, is it correct for me to say PANEL0_VDDEN corresponds to GPIO index 3 in the
VBT, and PANEL0_BKLTEN would be GPIO index 4? There's some evidence in
https://www.intel.ca/content/dam/www/public/us/en/documents/datasheets/pentium-celeron-n-series-j-series-datasheet-vol-1.pdf
which is for Apollo Lake, but it describes VDDEN and BKLTEN as for panel and
backlight enable, respectively.

So I checked further and found in
/sys/kernel/debug/pinctrl/INT3453:01/pinmux-pins the following:

...
pin 46 (PCIE_CLKREQ2_B): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 47 (PCIE_CLKREQ3_B): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 48 (HV_DDI0_DDC_SDA): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 49 (HV_DDI0_DDC_SCL): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 50 (HV_DDI1_DDC_SDA): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 51 (HV_DDI1_DDC_SCL): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 52 (PANEL0_VDDEN): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 53 (PANEL0_BKLTEN): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 54 (PANEL0_BKLTCTL): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 55 (HV_DDI0_HPD): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 56 (HV_DDI1_HPD): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 57 (HV_EDP_HPD): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 58 (GPIO_134): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 59 (GPIO_135): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 60 (GPIO_136): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 61 (GPIO_137): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 62 (GPIO_138): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 63 (GPIO_139): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 64 (GPIO_140): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 65 (GPIO_141): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 66 (GPIO_142): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 67 (GPIO_143): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 68 (GPIO_144): (MUX UNCLAIMED) INT3453:01:420
pin 69 (GPIO_145): (MUX UNCLAIMED) INT3453:01:421
pin 70 (GPIO_146): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 71 (LPC_ILB_SERIRQ): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 72 (LPC_CLKOUT0): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 73 (LPC_CLKOUT1): (MUX UNCLAIMED) (GPIO UNCLAIMED)
...

Take a look at pins 52 and 53, then at 68 and 69. I also did the following:

# cat /sys/kernel/debug/gpio
gpiochip3: GPIOs 297-331, parent: platform/INT3453:03, INT3453:03:

gpiochip2: GPIOs 332-351, parent: platform/INT3453:02, INT3453:02:
 gpio-336 (                    |0000:00:02.0        ) out hi 

gpiochip1: GPIOs 352-431, parent: platform/INT3453:01, INT3453:01:
 gpio-420 (                    |0000:00:02.0        ) out hi 
 gpio-421 (                    |0000:00:02.0        ) out hi 

gpiochip0: GPIOs 432-511, parent: platform/INT3453:00, INT3453:00:

(420-352 == 68)

I think that somehow the device we use devm_gpiod_get_index() on probably has a
wrong "base GPIO index" (just a hunch, if that exists at all).

I also tried manually writing to pins 52 and 53 using sysfs, which
unfortunately does nothing. I think, at least for my device, it's important to
do this in conjunction with MIPI_SEQ_DISPLAY_ON/MIPI_SEQ_DISPLAY_OFF.

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