Re: [PATCH net-next 0/5] net: phy: C45-over-C22 access

[Michael Walle <michael@walle.cc>]

>> The problem is in the middle.  get_phy_c45_devs_in_pkg() uses
>> mdiobus_c45_read(). Does mdiobus_c45_read() mean perform a C45 bus
>> transaction, or access the C45 address space? I would say it means
>> perform a C45 bus transaction. It does not take a phydev, so we are
>> below the concept of PHYs, and so C45 over C22 does not exist at this
>> level.
> 
> C45-over-C22 is a PHY thing, it isn't generic. We shouldn't go poking
> at the PHY C45-over-C22 registers unless we know for certain that the
> C22 device we are accessing is a PHY, otherwise we could be writing
> into e.g. a switch register or something else.
> 
> So, the mdiobus_* API should be the raw bus API. If we want C45 bus
> cycles then mdiobus_c45_*() is the API that gives us that, vs C22 bus
> cycles through the non-C45 API.
> 
> C45-over-C22 being a PHY thing is something that should be handled by
> phylib, and currently is. The phylib accessors there will use C45 or
> C45-over-C22 as appropriate.

I think the crux is get_phy_device(). It is used for two different
cases:
  (1) to scan the mdio bus
  (2) to add a c45 phy, i.e. in the DT/fwnode case

For (1) we must not use indirect access. And for (2) we know for
a fact that it must be a PHY and thus we can (and have to) fall back
to c45-over-c22.

Btw. for the DT case, it seems we need yet another property
to indicate broken MDIO busses.

-michael