Well,
The way to find out if your module loaded is to run lsmod
lsmod | grep rotaryfor example, will list any mods already loaded and contain the name "rotary".
If its there, after your insmod you can rest assured it’s installed correctly.
This does not mean however that our little configuration line bus0= was correct necessarily.
After loading it, run dmesg, perhaps grep that too for " rotary" and look in syslog for any output it may have logged, such as errors.
So, I wired up an encoder and loaded up the kernel modules. Unfortunately, I can’t find the necessary device from the rotary-gpio-custom module after loading it to bind to the rotary driver. When you have a platform device driver like the rotary one above, with “bind” you need to bind device to it.
From what I can find on the net, you need GPIO IRQs and I don’t know if the MT300N supports them.
I can see no way to use the rotary without some input from more experienced kernel/platform device developers or the developers of the modules.