On 3/7/21 8:37 PM, Chris Packham wrote:
[ ... ]

quoted

That's from -ENXIO which is used in only one place in i2c-mpc.c. I'll 
enable some debug and see what we get.

For the errant readings there was nothing abnormal reported by the driver.

For the "No such device or address" I saw "mpc-i2c ffe119000.i2c: No 
RXAK" which matches up with the -ENXIO return.

Id suggest to check the time until not busy and stop in mpc_xfer().
Those hot loops are unusual, and may well mess up the code especially
if preempt is enabled. Also, are you using interrupts or polling in
your system ? The interrupt handler looks a bit odd, with "Read again
to allow register to stabilise".

Do you have fsl,timeout set in the devicetree properties and, if so,
have you played with it ?

Other than that, the only other real idea I have would be to monitor
the i2c bus.

Guenter