quoted

IMHO adding functions to MMD modification would facilitate further
development (for example LED setup).

We already have some KSZ9477 specific initialization done in the Micrel
PHY driver under drivers/net/phy/micrel.c, can we converge on the PHY
driver which has a reasonable amount of infrastructure for dealing with
workarounds, indirect or direct MMD accesses etc.?

Actually the internal PHY used in the KSZ9897/KSZ9477/KSZ9893 switches
are special and only used inside those switches.  Putting all the switch
related code in Micrel PHY driver does not really help.  When the switch
is reset all those PHY registers need to be set again, but the PHY driver
only executes those code during PHY initialization.  I do not know if
there is a good way to tell the PHY to re-initialize again.
There is also a typo in one of those registers when the code was moved
to the Micrel PHY driver.  A fix will be needed.