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

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Message-ID: <87v99glnl8.fsf@waldekranz.com>
Date:   Wed, 24 Mar 2021 13:53:39 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     davem@...emloft.net, kuba@...nel.org, vivien.didelot@...il.com,
        f.fainelli@...il.com, olteanv@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: dsa: mv88e6xxx: Allow dynamic reconfiguration of tag protocol

On Wed, Mar 24, 2021 at 01:44, Andrew Lunn <andrew@...n.ch> wrote:
>> This was my initial approach. It gets quite messy though. Since taggers
>> can be modules, there is no way of knowing if a supplied protocol name
>> is garbage ("asdf"), or just part of a module in an initrd that is not
>> loaded yet when you are probing the tree.
>
> Hi Tobias
>
> I don't think that is an issue. We currently lookup the tagger in
> dsa_port_parse_cpu(). If it does not exist, we return
> -EPROBE_DEFER. Either it eventually gets loaded, or the driver core
> gives up. I don't see why the same cannot be done for a DT
> property. If dsa_find_tagger_by_name() does not find the tagger return
> -EPROBE_DEFER. Garbage will result in the switch never loading, and
> the DT writer will go find their typo.
>
>> Even when the tagger is available, there is no way to verify if the
>> driver is compatible with it.
>
> I would of though, calling the switch drivers change_tag_protocol() op
> will that for you. If it comes back with -EINVAL, or -EOPNOTSUPP, you
> know it is not compatible.
>
> So i guess i would keep all the code you are adding here to allow
> dynamic setting of the protocol. And add more code in
> dsa_switch_parse_of() to parse the optional tagging protocol name,
> error out -EPROBE_DEFER if it is not known yet, otherwise store it
> away in something like dst->tag_ops_name. And then probably in
> dsa_switch_setup(), if dst->tag_ops_name is not NULL, invoke the
> dynamic change code to perform the actual change.

Sounds like a plan. I will try it out and get back with a v2. Thanks.