Re: Circular dependency between DSA switch driver and tagging protocol driver

On 9/8/2021 5:26 PM, Vladimir Oltean wrote:

On Wed, Sep 08, 2021 at 03:14:51PM -0700, Florian Fainelli wrote:

quoted

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Where is the problem?

I'd say with 994d2cbb08ca, since the tagger now requires visibility into
sja1105_switch_ops which is not great, to say the least. You could solve
this by:

- splitting up the sja1150 between a library that contains
sja1105_switch_ops and does not contain the driver registration code

I've posted patches which more or less cheat the dependency by creating
a third module, as you suggest. The tagging protocol still depends on
the main module, now sans the call to dsa_register_switch, that is
provided by the third driver, sja1105_probe.ko, which as the name
suggests probes the hardware. The sja1105_probe.ko also depends on
sja1105.ko, so the insmod order needs to be:

insmod sja1105.ko
insmod tag_sja1105.ko
insmod sja1105_probe.ko

I am not really convinced that this change contributes to the overall
code organization and structure.

Yes, I don't really like it either, maybe we do need to resolve the other dependency created with 566b18c8b752 with a function pointer/indirect call that gets resolved at run-time, assuming the overhead is acceptable.

quoted

- finding a different way to do a dsa_switch_ops pointer comparison, by
e.g.: maintaining a boolean in dsa_port that tracks whether a particular
driver is backing that port

Maybe I just don't see how this would scale. So to clarify, are you
suggesting to add a struct dsa_port :: bool is_sja1105, which the
sja1105 driver would set to true in sja1105_setup?

Not necessarily something that is sja1105 specific, but something that indicates whether the tagger is operating with its intended switch driver, or with a "foreign" switch driver (say: dsa_loop for instance).

If this was not a driver I would be maintaining, just watching as a
reviewer, I believe "no" is what I would say to that.

-- 
Florian