Ethernet Switch Framework

[Warner Losh]

On Jan 28, 2012, at 4:00 PM, Juli Mallett wrote:
> It makes me wonder if the understanding of the relationship in FreeBSD
> isn't backwards.  Yes, the MAC sits on a bus and is memory-mapped, but
> you can conceptualize of it as a child of the PHY, rather than the
> parent of it, especially in systems with switch chipsets.  Especially
> in systems where there is a switch chipset attached to multiple MACs.
> 
> In that model, it makes sense to semi-generically attach a
> CPU-to-switch port's pseudo-PHY (or actual PHY, depending on hardware)
> to a MAC generically, but that doesn't meant that the switch itself is
> attached generically to the MAC.

I think that the main issue here is that we have an assumption that we have a tree structure.  However, it is more of a DAG across different domains.  The hierarchy works well when each device owns all the devices below it and only interacted with them.  Most devices are that way.  However, in the embedded world, there's lots of reach-accrosses that are expected that break the model.

Plus, MDIO is more than what we call mii/phy, so there's an imperfect match there.

Warner