Dynamically configured channels, overlap with GPIO, encoder support

["Giedrius Trainavičius" <giedrius@blokas.io>]

Hello,

I am developing an extension board for Raspberry Pi, it has a
microcontroller on it and I'm trying to expose its pins as a I/O
expander via I²C bus. I've recently successfully implemented gpiochip
interface as well as irq_chip in a kernel module, and now I'm looking
at adding ADC support, Industrial IO seems like a good candidate for
exposing it, but I have a couple of questions:

1. Can the IIO channels be configured dynamically? On the
microcontroller, the same pins can be used for GPIO, ADC, etc... - can
things like the channel direction, the function (simple high or low
GPIO pin, ADC, PWM output) be configured by userspace programs? Can it
be configured within a kernel module, if I provide my own sysfs
interface for function setup?

2. Can IIO channels be appended and removed to/from the list during runtime?

3. Are encoders supported by IIO? I'd like to decode encoders within
the firmware of the microcontroller, and provide only
increments/decrements to the kernel module via I²C, can encoders built
in such a way be exposed via IIO? I've seen some patches on the
internet adding 'counter' interface to IIO, but it seems it never made
it to be within IIO, and instead the 'counter' in its own subsystem.

4. How does IIO interact with gpiochip? As I'm implementing gpiochip
interface, I could simply return -EBUSY for pins already used by the
other subsystem.

Thank you!
Giedrius.