[Driver + Guide] Termux + RaspberryPi headless on OOS 11 / Serial Connection - OnePlus 7 & 7 Pro Cross Device Development

This thread is about on how to connect your OnePlus7 to an USB Serial device in order to use it headless.
Disclaimer
I am not responsible for any damage that may occure by following any instruction from here.
Dependencies:
Root. On OOS11 we don't lose anything by doing so... here is my guide
Kernel with version msm-4.14.190 (OOS 11.0.1.1 and older 11 OOS) (You can get your version in Settings -> Status -> Kernel-Version or type uname -r into a terminal emu)
Download
msm-4.14.190 serial module
Install and use
Install a custom kernel using 4.14.190. I've used blue_spark and installed it with franco kernel manager cause TWRP is not there yet. I paid it with the money i did not spend on Coffe2Go during the pandemic (Why? Because the modules compiled by me are not signed and the default kernel compiled by OnePlus does not allow them to be loaded)
Install Busybox for Android NDK in Magisk
Install Termux from F-Droid (Highly recommend F-Droid cause i had problems with the PlayStore version because the releases there are behind)
Load the drivers in Termux with su
insmod /sdcard/usbserial.ko
insmod /sdcard/ftdi_sio.ko or insmod /sdcard/ch341.ko depending on your serial converter chip
(After a reboot this needs to be done again)
(Unload: Currently only a reboot unloads the drivers. There is however no need for it)
Connect with microcom -s 115200 /dev/ttyUSB0
Replace 115200 with the speed you need
Fixing the terminal size
When connected, your terminal will be too small. We need to tell which size we need. So outside your serial type stty size. First number are the rows, secondly the columns. Then in your serial adopt them with stty rows * columns *. You could of course create a script that reads this value and sends the command automatic when connecting.
Baud speed
Support up to 1 Mbp/s (1000000 as baud argument) *as far as i know. I had problems using more. At baud speeds higher than 4 Mbp/s (4000000) also Microcom does not accept it.
Also great
You could now connect a bluetooth keyboard or make a hotspot (Internet access not needed) and / or start an ssh server. Then you could connect to it with another device like an iPad or any ssh capable device.
Raspberry + Serial connection example
On Raspberry boot/config add enable_uart=1
Make sure the jumper is set to 3.3V
Connect:
GND (Raspi) -> GNU (FTDI)
Tx (Raspi) -> Rx (FTDI)
Rx (Raspi) -> Tx (FTDI)
Connect the Serial converter to your phone (using USB-C adapter)
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Source
https://github.com/trueToastedCode/android_kernel_oneplus7_sm8150