Re: [PATCH V2 1/3] Documentation: devicetree: add multiple cpu port DSA binding

[Florian Fainelli <f.fainelli@gmail.com>]

On 06/07/2017 02:10 PM, Rob Herring wrote:
> On Tue, May 30, 2017 at 02:32:29PM -0700, Florian Fainelli wrote:
>> On 05/30/2017 03:44 AM, John Crispin wrote:
>>> Extend the DSA binding documentation, adding the new property required
>>> when there is more than one CPU port attached to the switch.
>>>
>>> Cc: Rob Herring <robh+dt@kernel.org>
>>> Cc: devicetree@vger.kernel.org
>>> Signed-off-by: John Crispin <john@phrozen.org>
>>> ---
>>>  Documentation/devicetree/bindings/net/dsa/dsa.txt | 61 ++++++++++++++++++++++-
>>>  1 file changed, 60 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/net/dsa/dsa.txt b/Documentation/devicetree/bindings/net/dsa/dsa.txt
>>> index cfe8f64eca4f..c164eb38ccc5 100644
>>> --- a/Documentation/devicetree/bindings/net/dsa/dsa.txt
>>> +++ b/Documentation/devicetree/bindings/net/dsa/dsa.txt
>>> @@ -55,6 +55,11 @@ A user port has the following optional property:
>>>  - label			: Describes the label associated with this port, which
>>>                            will become the netdev name.
>>>  
>>> +- cpu			: Option for non "cpu"/"dsa" ports. A phandle to a
>>> +			  "cpu" port, which will be used for passing packets
>>> +			  from this port to the host. If not present, the first
>>> +			  "cpu" port will be used.
>>
>> So this option essentially allow us to "partition" the switch between
>> vectors of ports and their upstream/CPU port.
> 
> Could this be more generic? This is basically saying route all packets 
> on this port to another port. Maybe there's some usecase to route to 
> non-cpu ports?

Yes, we absolutely want it to be more generic. The "problem" is that
before an user has a chance to come in and type some commands that
reconfigure the switch, there is a default state in which we need to
assume one particular CPU/management port is going to be used to receive
traffic. This can be pushed as a driver decision as to which of the
multiple CPU ports is the most suitable IMHO.

> 
>> While using Device Tree is an obvious choice for making the initial
>> partitioning, it seems like we are missing a configuration mechanism
>> whereby we can properly assign ports to a specific upstream CPU port.
> 
> What determines how things are routed/partitioned? If it is purely user 
> choice then I don't think this should be in DT.

Right now we don't have any mechanism, and statically doing this from
Device Tree is too inflexible. I have been working on a parallel path
where we use the bridge (which is already accelerated when there is a
switch) in order to define groups of ports, the idea would be do to e.g:

brctl addbr br-lan
brctl addbr br-lan eth0
brctl addbr br-lan lan1
...
brctl addbr br-lan lan4

brctl addbr br-wan
brctl addbr br-wan eth1
brctl addbr br-wan wan

Assuming that lan1-lan4 are your LAN ports, and wan is your WAN port and
you have two CPU ports.

Until we configure these bridges though, we would be in the same state
that we currently are, which is that traffic is only possible between
lan1 <-> eth0, lan2 <-> eth0 and so on (every port is isolated from each
other).
-- 
Florian