Re: [PATCH net-next v7 4/9] net: dsa: lan9645x: add basic dsa driver for LAN9645X

[Jens Emil Schulz Ostergaard <jensemil.schulzostergaard@microchip.com>]

On Mon, 2026-06-08 at 20:00 +0200, Andrew Lunn wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> > +     dsa_switch_for_each_user_port(dp, ds) {
> > +             if (dp->cpu_dp->ds != ds) {
> > +                     dev_err(ds->dev,
> > +                             "NPI port on a remote switch is not supported\n");
> > +                     return -EINVAL;
> > +             }
> > +
> > +             if (first_cpu_dp && dp->cpu_dp != first_cpu_dp) {
> > +                     dev_err(ds->dev, "Multiple NPI ports not supported\n");
> > +                     return -EINVAL;
> > +             }
> > +
> > +             first_cpu_dp = dp->cpu_dp;
> 
> The reason i asked about NPI ports is because this is looping over
> user ports. Yet you say one of these user ports is a CPU port. That
> cannot be correct.
> 
> The first port returned by dsa_tree_for_each_cpu_port() would be
> first_cpu_dp.
> 
>         Andrew


I tried to mimic the approach in drivers/net/dsa/ocelot/felix.c:

static int felix_tag_npi_setup(struct dsa_switch *ds)
{
	struct dsa_port *dp, *first_cpu_dp = NULL;
	struct ocelot *ocelot = ds->priv;

	dsa_switch_for_each_user_port(dp, ds) {
		if (first_cpu_dp && dp->cpu_dp != first_cpu_dp) {
			dev_err(ds->dev, "Multiple NPI ports not supported\n");
			return -EINVAL;
		}

		first_cpu_dp = dp->cpu_dp;
	}

	if (!first_cpu_dp)
		return -EINVAL;

	felix_npi_port_init(ocelot, first_cpu_dp->index);

	return 0;
}

Perhaps I misunderstand you, but there could be confusion about
terminology. The chip designers have a concept of CPU port, which is
used liberally in the datasheet, and in this driver code.

However, the concept is different from the DSA concept of a CPU port.
Let us call the first switch CPU port, and the second DSA CPU port.

The port we want to use as a DSA CPU port, i.e. the port with the
'ethernet = <&host_port>;' property in the device tree, will be
configured to be an NPI port for injection/extraction for the switch CPU
port (which is not a physical port on the device).

Therefore, this NPI port is not iterated by
dsa_switch_for_each_user_port. The switch CPU port (index 9) is also not
iterated by it. It is a chip internal construct with no representation
in the device tree, and no struct dsa_port.


Thanks,
Emil