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

From: Florian Fainelli <[email-masked]>
Date: Wed, 30 Sep 2015 14:33:42 -0700

On 30/09/15 14:27, Tim Harvey wrote:
> On Wed, Sep 30, 2015 at 2:12 PM, Andrew Lunn <[email-masked]> 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.

Even though a bus is completely auto-discoverable, if there is
additional information needed to supplement that topology, having things
be represented in Device Tree is typically accepted.

> 
>>
>>> 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.

You can register a network device notifier, and try to extract that
information about this network device you need once you see that device
being registered. As an example, there is a loopback/fake DSA switch
driver here which uses the loopback interface as a parent network device
(NB: this is using the network device name, which is pretty lame, but
that does the job):

https://github.com/ffainelli/linux/commit/67d1db45d17f8cc3b32d7a46c49d5df736cee56c
-- 
Florian