Re: (Ab?)use of MII

[Wolfgang Solfrank <Wolfgang%Solfrank.net@localhost>]

Hi Thor,

sorry for the late reply, I was out of town.

>> so I've got NetBSD running on my Banana Pi BPi-R1.
>>
>> With this board, the gigabit net interface on the processor chip is
>> connected via mii to a switch chip (BCM 53125). The 5 external ports
>> of this chip all have their own phys and are brought out for external
>> connection.
> 
> This is an RMII configuration, right, not normal MII?

Yes.

>> With an unmodified BPI kernel, the mii attach code finds all of those
>> phys via the mii bus of the processor's ethernet interface and then
>> enables only one of those.
> 
> That seems exceedingly odd.  I don't know this particular switch chip,
> but, usually, in this kind of reverse-MII setup, the switch chip provides
> one MII per port (or one quad-MII per 4 ports, using quad PHYs, but those
> look logically like 4 MIIs except for a minimal set of shared PHY registers)
> and the CPU is hooked up just like the PHYs for the physical ports.
> 
> I have not seen all the MIIs bridged together as you describe.  Is there a
> different mode for the switch in which it doesn't do this?  I am reasonably
> familiar with the Marvell switch parts and a few others; not so much the
> Broadcoms.

It is possible to access the internal registers of the switch via an
SPI interface.  Or the device can be initialized from some EEPROM.
However, those don't seem to be wired on this board. Alternatively:
"The BCM53125U offers an MDC/MDIO interface for accessing the switch
registers as well as the PHY registers. An external management entity
can access the switch registers through this interface when the SPI
interface is not used.  (That is, when the SPI clock is in idle mode.)
The switch registers are accessed through the Pseudo PHY interface,
and the PHY registers are accessed directly by using PHY addresses."

The 5 PHYs on the external ports are found at addresses 0-4, and the
Pseudo PHY, which addresses the internal registers of the switch, is
found at address 0x1e.

Ciao,
Wolfgang
-- 
Wolfgang%Solfrank.net@localhost				Wolfgang Solfrank