Hello Parvaneh, (sorry if I got your name wrong on my first response)
I'm using Beaglebone black board for my demo. It seems that there is not GPIO driver for this platform. I wanted to know is there any documentation of GPIO driver for me to understand the other platforms driver and write the driver code for am335x?
As far as I know, each platform has its own programming model and quirks, and is very different from each other. So basing your GPIO driver on another platform might not be a very good idea, unless of course they share the same designer and are pretty similar. However, I believe we don't have the GPIO drivers for platforms similar to the am335x, so the best option would be to either consult the technical reference manual for the am335x or look at the U-Boot or Linux sources for an example. Sincerely, Damon