On Mon, Feb 29, 2016 at 04:43:16PM -0500, Murali Karicheri wrote:

Hi Murali

Please can you get your email client to wrap lines at ~ 75 characters.

TI Keystone netcp h/w has a switch. It has n slave ports and 1 host
port. Currently the netcp driver disables the switch functionality
which makes them appear as n nic ports. However we have requirement
to add switch support in the driver. I have reviewed the
experimental driver documentation
Documentation/networking/switchdev.txt and would like to understand
it better so that I can add this support to keystone netcp driver.

NetCP h/w has a 1 (host port) x n (slave port) switch. It can do
layer 2 forwarding between ports. In the switch mode, host driver
provides the frame to the switch and switch uses the filter data
base (AKA ALE table, Address Learning Engine table) to forward the
packet. There is a piece of information available per frame (meta
data) to decide if frame to be forwarded to a particular port or use
the fdb for forward decisions.

This makes is sound like a good fit for DSA.

Documentation/networking/dsa/dsa.txt.

You probably need to implement a new tagging protocol in
net/dsa/tag_*.c and a driver in drivers/net/dsa/

1. How does port netdev differ from regular netdev that carries data
   when registering netdev? Any example you can point to?

They don't differ at all. You consider each port of the switch to be a
normal Linux interface.

2. I assume port netdev will appear as an interface in ifconfig -a
   command and it is not assigned an IP address. Correct?

The user can assign an address, if they want. It is a normal Linux
interface. They can also create a bridge, and add the interface to the
bridge. An advanced DSA driver will keep track of which interfaces are
in which bridge, and if possible, offload the bridge to the hardware.

3. with 1xn switch, so we have n + 1 netdev registered with net
   core? I assume, only 1 netdev is for data plane and the rest are
   control plane. Is this correct?

No. You only have netdev devices for the external ports of the
switch. The other port is known as the cpu port, and does not have a
netdev.

4. We have bunch of port specific configuration that we would like
to control or configure from use space using standard tools. For
example, switch port state, flow control etc. Is that possible to
add using this framework? ethtool update needed for this?

The whole idea here is that the switch ports are normal Linux
interface. You use normal linux APIs to configure them. You probably
don't need to add any new features.

One key things to get your head around. The switch is a hardware
accelerator for the Linux stack. You have to think how you can make
your switch accelerate the Linux stack. It takes people a while to get
this.

      Andrew