[U-Boot] U-Boot Device Driver Development Guide

[jerroldm at blackmagicdesign.com]

Dear Sir,
 
I am considering using U-Boot as a software platform to bring up a hardware platform that am developing.  In doing so, I may need to develop a couple of Device Drivers.  I was wondering if anyone could point me to a document or a website that might help guide me to do this in the correction fashion.
 
To be a bit more specific, I have a custom UHS-II SD Card Host Controller which I would like to access through FAT and EXFAT commands.  I am using a Zynq FPGA as a platform.
 
Thank you,
 
Jerrold