Hello Andrew and all,
I was recently debugging an issue in the FEC driver, about 2% of the
time the driver is failing with "MDIO read timeout" at boot on a 5.4
kernel.

This issue is not new and from time to time appear again, it seems that
the previous interrupt based mechanism is somehow easy to break.

I backported your patch
f166f890c8f0 (net: ethernet: fec: Replace interrupt driven MDIO with polled IO, 2020-05-02)
to kernel 5.4 and it seems that it fixes the issue (I was able to do 470
power cycles, while before it was failing after a couple of hundreds
cycles best case).

Shouldn't this patch be backported to kernel 5.4? 

Francesco