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

[Peter Crosthwaite]

On Mon, Jan 6, 2014 at 1:27 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Thu, Jan 02, 2014 at 08:25:10PM +1000, Peter Crosthwaite wrote:
>> Hi Beniamino,
>>
>> On Thu, Jan 2, 2014 at 7:18 PM, Beniamino Galvani <address@hidden> wrote:
>> > This patch adds support for the Fast Ethernet MAC found on Allwinner
>> > SoCs, together with a basic emulation of Realtek RTL8201CP PHY.
>> >
>>
>> 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).

Regards,
Peter

> Stefan
>