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From: Warner Losh <imp@bsdimp.com>
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To: Juli Mallett <jmallett@FreeBSD.org>
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Cc: Aleksandr Rybalko <ray@ddteam.net>, Stefan Bethke <stb@lassitu.de>,
	freebsd-net@FreeBSD.org, Adrian Chadd <adrian@FreeBSD.org>,
	Aleksandr Rybalko <ray@FreeBSD.org>, freebsd-arch@FreeBSD.org
Subject: Re: Ethernet Switch Framework
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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.
>=20
> 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