netdev - Re: DSA driver - how to glue to a PCI based NIC's mdio?

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Message-ID: <CAJ+vNU2SUpsQ+7dwPfR6EHVofpvVFF42KO=YUDaarLaDwWvXFw@mail.gmail.com>
Date:	Wed, 30 Sep 2015 14:27:19 -0700
From:	Tim Harvey <tharvey@...eworks.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: Re: DSA driver - how to glue to a PCI based NIC's mdio?

On Wed, Sep 30, 2015 at 2:12 PM, Andrew Lunn <andrew@...n.ch> wrote:
> On Wed, Sep 30, 2015 at 01:44:52PM -0700, Tim Harvey wrote:
>> Greetings,
>>
>> I'm working on adding DSA support for a PCIe expansion card (designed
>> by us) that has common PCIe NIC connected via its mii-bus to a Marvell
>> MV88E6171. Because the NIC is a PCIe device, it has no device-tree
>> representation of its NIC or its mdio bus, but does register its mdio
>> bus with Linux.
>
> It is possible to represent PCIe devices in device tree. Take a look
> at ePAPR. Is the PCIe host in DT?

It is possible to represent PCI devices in device-tree however not in
a dynamic or plug-able fashion - they have to be nested per bus/slot
which defeats the purpose of dynamic enumeration.

>
>> Perhaps the right approach is to program the NIC's EEPROM on our board
>> with a PCI_ID/DEVICE_ID of ours, add support for those ID's to the
>> NIC's driver, and within the NIC's driver create and register dsa
>> platform device when our ID is encountered?
>
> This sounds sensible. But i doubt you can add your DSA platform
> information to the NIC's device driver. Better would be to have a
> small shim driver which is loaded on your PCI_ID/DEVICE_ID. That would
> instantiate the NIC driver, and insert a DSA platform device.

I was thinking of this as well, but then I would still need that shim
to know the netdevice that the driver I'm shimming creates so I can't
figure a way to do it without touching the PCI driver.

Tim
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