Embedded switch instead of stadard PHY

[Warner Losh]

On May 9, 2011, at 12:30 AM, Adrian Chadd wrote:

> On 8 May 2011 21:16, Marius Strobl <marius at alchemy.franken.de> wrote:
> 
> [snip]
> 
>> Depends on what you understand by properly. One idea I particularly
>> like is to handle switch ports as pseudo-interfaces hanging off of the
>> the MAC driver parent roughly similar to vlan(4). That way you'd have
>> per port link status and could configure the media.
> 
> The reason I like this is because I realise that these switch PHYs
> tend to have quite a bit of varying but useful functionality, that
> isn't just "multi-port single-VLAN switch PHY."
> 
> Besides there being per-port status, there can also be per-port
> error/packet/byte counts, VLAN setups (tagged/untagged), QoS
> configuration, sometimes some L2 filtering and (even more creepy)
> sometimes L3 filtering/routing.
> 
> They can sometimes hang off the MII bus, but ISTR datasheets which
> show they can hang off an SPI bus too. So although they can look like
> PHYs complete with the register layouts, there's extended commands to
> implement other features as well. There may even be more than one CPU
> ethernet port hooked up - I think the Routerstation Pro has both CPU
> GigE ports wired to the switch PHY and defaults to mapping port 1 ->
> arge0 and Port 2,3,4,5 -> arge1.
> 
> I'd really appreciate it if someone were able to sit down, take the
> existing work done by Luiz and others and flesh out a bare minimum set
> of switch PHY drivers that configure them with some sensible defaults
> (rather than leaving it up to the boot firmware to do it for you) and
> have all of the interface/configuration glue in the kernel. As I said
> earlier, figuring out how to expose all the functionality - including
> per-port error counts and such - can come later.

Yes.  Agreed.  Stated a bit more elegantly than I just did...  Handling non-localized connections is critical here.  The embedded world has a lot of funky interconnects that map poorly into our device model.  Having the association handled at a higher level will help us connect these things.  In the designs I've seen, this can happen both for the switches we're talking about, as well as PHYs.  I believe there are some CPUs where talking to the PHY doesn't go through the MAC....

Warner