I am trying to access GPIOs on IMX 8M Plus EVK the SPF-46370_A3.pdf has some information on GPIOs.. Attached a snapshot from page 18. Image shows GPIO available but what GPIO bank they belong to and what is the number is not clear. Pls refer attached image GPIO21 to 29 but how do I know which GPIO bank they belong to and number so that I can use Linux Sysfs commands and verify the GPIOs.
You need to track down the signals to know where they come from and use the config tools or the reference manual to know which bank of memory they belong, from your example (GPIO21 to 29) the first 3 GPIO's correspond to an i2c expander, so they are controlled with that expander, let's look at the GPIO25.
If you look at the schematic this come from a Dual-Supply Translating Transceiver, basically, the function is like a buffer:
So considering this you can see that comes from SAI5_RXD1, so if you look at this on the config tools, here you have the connection to that pin and GPIO bank they belong to:
But as I said earlier you could also use the reference manual, please see below:
I left the links from the config tools and the reference manual:
Config Tools for i.MX Applications Processors
i.MX 8M Plus Applications Processor Reference Manual
Hope this helps you.