Wiring encoder to LinuxCNC + Mesa vs motor controller

Oh! I thought feedback would be required for coordinated motion.

What are the limitations or benefits without/with encoder feedback to LinuxCNC+Mesa?

One advantage, If you have step/dir servos, returning the position information to LinuxCNC
allows LinuxCNC to monitor the actual following error during operation.

How much of an accuracy/performance impact would there be if running LinuxCNC + Mesa without encoder feedback, while having the encoder feedback to the ODrive motor controller?

I depends on the ODrive performance and tuning, It there a tuning program for the drive?
 

Yes, the ODrive (Pro) has extensive options for configuration; PID tuning; torque, velocity, position, and trajectory control modes, etc.

Some initial PID tuning was already done, and the intention is to run it in position control mode, driven by step/dir from Mesa + LinuxCNC.

In my original post in this thread, I linked a forum thread in which an ODrive development engineer didn't see an issue connecting an incremental encoder to both ODrive and Mesa + LinuxCNC. In response to concerns about signal levels or ground loops, his response was that "The [ODrive] Pro has common-mode filtered encoder inputs, so it should be able to withstand some AC-mode ground differential. But you can actually make it fully isolated – if you desolder [a couple of components], it’ll isolate the the A/B/Z and Hall encoder inputs". 

So there are a few possible approaches and I'm trying to understand what makes the most sense:

* Encoder feedback to ODrive with LinuxCNC + Mesa in open loop (simplest but accuracy concerns?)
* Encoder feedback directly to both ODrive and LinuxCNC + Mesa (potential signal/ground loop issues, maybe worth a shot anyway)
* Two separate encoders for independent feedback to ODrive and Mesa + LinuxCNC (added cost in funds and space on machine)