Re: Dynamically configured channels, overlap with GPIO, encoder support

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Tue, Jun 28, 2022 at 12:06 PM Giedrius Trainavičius
<giedrius@blokas.io> wrote:
>
> 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.

We have a DLN2 adapter that provides 4 interfaces with overlapped GPIO
pins, I don't remember how they solved this. Perhaps the
microcontroller itself refuses GPIO line acquisition when it's in use
for other functions.

Hence, I recommend looking into the drivers for Diolan DLN2.


-- 
With Best Regards,
Andy Shevchenko