[PATCH] board: sl28: add DSA support for variant 2

[Vladimir Oltean]

On Tue, Feb 16, 2021 at 11:25:25PM +0100, Michael Walle wrote:
> Now that u-boot gained DSA support, and it is already enabled for the
> kontron_sl28 board, add the last missing piece and enable the
> corresponding devices it in the device tree.
> 
> Signed-off-by: Michael Walle <michael at walle.cc>
> ---
>  .../arm/dts/fsl-ls1028a-kontron-sl28-var2.dts | 46 +++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/arch/arm/dts/fsl-ls1028a-kontron-sl28-var2.dts b/arch/arm/dts/fsl-ls1028a-kontron-sl28-var2.dts
> index 1ea1265bcf..39280cd1c7 100644
> --- a/arch/arm/dts/fsl-ls1028a-kontron-sl28-var2.dts
> +++ b/arch/arm/dts/fsl-ls1028a-kontron-sl28-var2.dts
> @@ -15,6 +15,12 @@
>  / {
>  	model = "Kontron SMARC-sAL28 (TSN-on-module)";
>  	compatible = "kontron,sl28-var2", "kontron,sl28", "fsl,ls1028a";
> +
> +	aliases {
> +		eth0 = &mscc_felix_port0;
> +		eth1 = &mscc_felix_port1;
> +		eth2 = &enetc2;

The way DSA is intended to be used is that the alias for the DSA master
(host port) comes first, then the alias for switch ports.

The reasoning is that U-Boot has MAC address inheritance rules. If
ethNaddr (where N is the sequence id of the Ethernet udevice
corresponding to a switch port) is not defined in the env, then the MAC
address is inherited from the master interface.

But the address cannot be inherited unless the master has already been
probed. So it must be probed first, so it needs to have a lower numbered
alias.