Re: [Qemu-devel] [PATCH 1/2] hw/net: add support for Allwinner EMAC Fast Ethernet controller

[Beniamino Galvani <b.galvani@gmail.com>]

On Mon, Jan 06, 2014 at 02:12:27PM +0800, Stefan Hajnoczi wrote:
> > >> More a comment for net in general, but I think sooner or later we need
> > >> to move towards a split between phy and mac on the device level.
> > >> continuing the phy-within-mac philosophy is going to make the
> > >> socification efforts awkward. Are MII and friends a busses (as in
> > >> TYPE_BUS) in their own right, and connection of mac and phy has to
> > >> happen on the board level?
> > >
> > > I see PHY and MAC split as advantageous because it allows code reuse and
> > > better testing.  The main thing I'd like to see is PHY device tests
> > > using tests/libqtest.h.
> > >
> > > If someone wants to implement it, great.  It would make it easier to add
> > > more NIC models in the future.
> > >
> > > Regarding SOCification and busses, I'm not sure.  Is it okay to just say
> > > a NIC has-a PHY (i.e. composition)?
> > >
> > 
> > Generally speaking, in the (ARM) SoCification the MAC is part of the
> > SoC which in the latest styling guidelines is a composite device. This
> > composite is supposed to reflect the self contained SoC product which
> > the PHY is usually not a part of. So we have two opposing compositions
> > here:
> > 
> > NIC = MAC + PHY
> > SOC = CPUs + MAC + ...
> > 
> > MAC can't be in both. So for SoCs the NIC concept needs to abandoned.
> > After all the expansion of NIC as "Network Interface Card" is a little
> > bit PCish. Your average SoC networking solution has no such "card".
> > Just an on chip MAC (same pacakge/die as CPU etc) connecting to a PHY
> > via PCB traces.
> > 
> > So I think long term, MII has to be a TYPE_BUS that is visible on the
> > top level SoC device. Self contained NICs (as we know them today) are
> > then also implementable as container devices (of MAC and PHY) that use
> > this bus internally (in much the same way the SoC boards would attach
> > external PHY to SoC).
> 
> Okay, that makes sense.  Given the amount of emulated hardware in QEMU
> today, I think it would be okay to simply add new MAC/PHYs while still
> supporting the NICs of old.  If someone is enthusiastic about
> refactoring and testing existing NICs then great.  But I think it's more
> pragmatic to simply start working with a split MAC/PHY where that is
> beneficial.

Regarding the patch, can I resubmit it with MAC and PHY modeled as a
single device? Or it's better to start thinking on how to implement
proper MAC/PHY split?

Beniamino