Refine I2C error outcomes - e.g. expose NACK separately somehow.

[bscarlet]

Some I2C devices communicate important state with I2C NACK - e.g. an EEPROM (such as the Microchip 24AA02E48) might report NACK while it's busy completing a write operation. The current Zephyr I2C API does not distinguish NACK from other non-success conditions, such as loss of arbitration - the different cases are all reported with a return code of -EIO. This makes writing a driver for such devices awkward, as to wait and retry when getting a NACK one apparently must react to more serious errors the same way.

I request that more fine-grained information about I2C errors be exposed somehow. For example, NACK in particular might be handled by returning a different return code - perhaps -EAGAIN. Alternately, the current API could be extended with a new function to return a more fine-grained I2C specific enum after an error occurs.

[henrikbrixandersen]

I believe Linux uses -ENXIO for I2C NACK. I think -EAGAIN should be reserved for situations that are universally retryable.

[zephyrbot]

Hi @teburd,

This issue, marked as an Enhancement, was opened a while ago and did not get any traction. It was just assigned to you based on the labels. If you don't consider yourself the right person to address this issue, please re-assing it to the right person.

Please take a moment to review if the issue is still relevant to the project. If it is, please provide feedback and direction on how to move forward. If it is not, has already been addressed, is a duplicate, or is no longer relevant, please close it with a short comment explaining the reason.

@bscarlet you are also encouraged to help moving this issue forward by providing additional information and confirming this request/issue is still relevant to you.

Thanks!