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Date:      Sun, 29 Jan 2012 00:05:50 -0700
From:      Warner Losh <imp@bsdimp.com>
To:        Juli Mallett <jmallett@FreeBSD.org>
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
Message-ID:  <DBAB0C5C-5B2D-4430-8096-9E4DC7233961@bsdimp.com>
In-Reply-To: <CACVs6=-U9rr7cpeJ%2BVUgP3Xq1yRB=Xk1GjuzEOuXiEUoqGFq_Q@mail.gmail.com>
References:  <20120120221319.ca8b631f.ray@freebsd.org> <30A45A1E-CA13-4AC8-86FB-F8E06301D1F6@lassitu.de> <20120122195130.360261ce.ray@freebsd.org> <CAJ-VmokTh2q0ZH=kwU6GzJm5Mr4k7geJiFsoX_A9hcLhMZNxsg@mail.gmail.com> <0E31FEC4-963D-4AC8-9AB7-EE6D6D7F86EE@lassitu.de> <CAJ-Vmo=GRKRf%2BYsFqNm9d_T3Tq583uV_pabMV6ozuaytSRLivg@mail.gmail.com> <20120129001251.7e4cfe83.ray@ddteam.net> <CACVs6=-U9rr7cpeJ%2BVUgP3Xq1yRB=Xk1GjuzEOuXiEUoqGFq_Q@mail.gmail.com>

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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




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