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

Tobias Waldekranz
2021-04-06T09:07:38Z

On Sun, Mar 28, 2021 at 17:24, Andrew Lunn <andrew@lunn.ch> wrote:
> 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

Since DSA is supported on all devices, perhaps we should just have:

enum mv88e6xxx_edsa_support {
MV88E6XXX_EDSA_UNSUPPORTED,
MV88E6XXX_EDSA_UNDOCUMENTED,
MV88E6XXX_EDSA_SUPPORTED,
};

?

Do we also want to default to DSA on all devices unless there is a
DT-property saying something else? Using EDSA does not really give you
anything over bare tags anymore. You have fixed the tcpdump-issue, and
the tagger drivers have been unified so there should be no risk of any
regressions there either.