I am not talking about PostmarketOS or similar large community projects, just small single person hobby projects.
And are there any resourc guide on creating a simple kernel which shows "Hello world" in the phone boot screen like x86 kernel project guides?
Can anyone share the links for OS development resource in android phones and resource for understanding android mobile hardware?
If truly custom OS/Kernel is what you want, someone was trying to run NuttX RTOS on Pinephone:
1) Booting NuttX: https://lupyuen.github.io/articles/uboot 2) Writing an LCD Driver: https://lupyuen.github.io/articles/dsi2 3) Getting a basic terminal running using LVGL: https://lupyuen.github.io/articles/terminal
I'd still recommend trying to port PostmarketOS/Ubuntu touch/Sailfish OS etc.. to your phone first. That can be a good beginner friendly way to understand what happens on your smart phone: the boot process, software stack etc.. and then you can go deeper by either customizing the software (Boot into a little web browser and call it a web phone etc..)/drivers to your liking (Adding features like double tap to wake)/trying to port mainline kernel to them.
I think reality is somewhere in between. End users of mobile phones are a threat vector to carrier infrastructure. Phones obsoless quickly because electronics manufacture is so fluid.
To put it another way, producing comprehensive technical documentation would probably take longer than the product life cycle of the products documented, and the fat part of the belle-curve of comprehensive documentation use cases is amateur experimentation.
In other words, there's no reasonable business case for giving you ready access to technical documentation and a lot of reasonable business cases against it.
I am not saying this is good. Not saying it is bad. It just is and therefore is not worth having an opinion on because I am not in a position to change it. Probably noone is, it's too complex.