[PORT] Help Porting U-BOOT master branch to GT90X V4 sun7i a20 tablet board

[Koray Bilir]

hello to the u-boot community, last week i wanted to do some hardware
hacking and came across one of my nameless chinese brand sun7i a20 tablets
poked around in adb shell, mounted the NANDA partition and to my surprise
it was running u-boot v2011 , so i wanted to put a linux kernel on there to
see if it would boot
unfortunately the u-boot was outdated and couldn't boot it, tl dr; i am
trying to write a device tree file so i can successfully port U-BOOT
v2021.07-rc2-00238-geb53b943be-dirty.
So far I have "successfully" compiled a u-boot.bin although binman gives an
error of "cant find u-boot.dtb" the u-boot.bin works fine on the device.
Sorry for my rambling. I just wanna give the most information in one post.
so far I was able to write a simple .dts file for my board to get the debug
uart ports working. luckily I discovered some test points on the board that
were for uart tx rx.
I got the uart interface working. I don't have an ftdi at the moment so i'm
using an arduino as an usb to serial passthrough long story short i was
able to get the u boot shell working
and I was able to interface with the device. since its my first time cross
compiling, u-boot and also device tree files i need some guidance to where
should i look, one question that i have is
Is there any pre-made building environments that I can just run on a
virtual machine, im currently using my laptop which has debian 10 on it to
compile and i'm not sure if I did everything right to get my build
environment working. I have access to the stock rom of my device so i cant
brick it and also i have access to the source code of the u-boot 2011
version that was on the board from
the factory. unfortunately this device has android 4.2.2 installed on it
and i couldn't find any device tree files on it, i have the sysconfig.fex
file that has the pinouts and config data on it
So basically I'm trying to convert the sysconfig.fex to a dts file.

my objectives right now are:
setup ram correctly
get nand working
get sd/mmc working
get usb working
get 24bit lvds panel working
get touchscreen working
get audio working
and finally get some sensors working that the board has

I'm having no luck getting the nand and lvds panel working. I haven't tried
sd/mmc , audio and touchscreen but i had usb working with some settings, i
disabled it when i was debugging for other stuff.
This gt90x v4 board is found in many nameless chinese tablets so I'm hoping
this little project of mine can help others.
also i see an unpopulated place that could take another nand chip , i'll
have to try to see if it would work
if any of you are interested in this or want to look at everything i got i
can for the u-boot repository and commit my changes there and if any of you
want to help you are more than welcome since
this is my first time doing embedded stuff im learning as i go along so
feel free to correct me.
I can provide the source code of the 2011 u-boot that had everything
working on the device and I can provide everything I have mentioned earlier
(file wise).

Let's get to the board details.

ALLWINNER A20 SUN7I DUAL CORE CPU
2x NANYA MTT 256X16DDR3 V 1330 RAM CHIPS (device supposedly has 1gb of ram)
TOSHIBA JP5415 TAIWAN 13359 A E / TC58TEG6DCJTA00 (8GB NAND)
AXP209 0448CB 66K1
GSL3680 64A0D4281N
REALTEK RTL8188ETV D700331 GD27
E203460 9INCH 1024X600 24BIT  LVDS PANEL

Thats all of the major components on the board that i can see, i'll have an
image of the board down below.
https://drive.google.com/drive/folders/17zZTsgPHKktV4VARHAxR8tpHS4P04U7x?usp=sharing

I would be super happy if anyone is able to point me in the right direction
or help me.

-Koray