Re: [PATCH net-next 1/3] net: dsa: mv88e6xxx: Allow dynamic reconfiguration of tag protocol

Andrew Lunn
2021-03-28T15:25:50Z

On Fri, Mar 26, 2021 at 11:56:46AM +0100, Tobias Waldekranz wrote:
> All devices are capable of using regular DSA tags. Support for
> Ethertyped DSA tags sort into three categories:
>
> 1. No support. Older chips fall into this category.
>
> 2. Full support. Datasheet explicitly supports configuring the CPU
> port to receive FORWARDs with a DSA tag.
>
> 3. Undocumented support. Datasheet lists the configuration from
> category 2 as "reserved for future use", but does empirically
> behave like a category 2 device.

> +static int mv88e6xxx_change_tag_protocol(struct dsa_switch *ds, int port,
> + enum dsa_tag_protocol proto)
> +{
> + struct mv88e6xxx_chip *chip = ds->priv;
> + enum dsa_tag_protocol old_protocol;
> + int err;
> +
> + switch (proto) {
> + case DSA_TAG_PROTO_EDSA:
> + if (chip->info->tag_protocol != DSA_TAG_PROTO_EDSA)
> + dev_warn(chip->dev, "Relying on undocumented EDSA tagging behavior\n");
> +
> + break;
> + case DSA_TAG_PROTO_DSA:
> + break;
> + default:
> + return -EPROTONOSUPPORT;
> + }

You are handling cases 2 and 3 here, but not 1. Which makes it a bit
of a foot cannon for older devices.

Now that we have chip->tag_protocol, maybe we should change
chip->info->tag_protocol to mean supported protocols?

BIT(0) DSA
BIT(1) EDSA
BIT(2) Undocumented EDSA

Andrew