netdev - Re: [PATCH RFC net-next 3/6] net: dsa: sja1105: use .mac_select

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Date:   Fri, 25 Feb 2022 13:25:50 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Marek Beh__n <kabel@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next 3/6] net: dsa: sja1105: use
 .mac_select_pcs() interface

On Fri, Feb 25, 2022 at 10:57:40AM +0000, Russell King (Oracle) wrote:
> > > -	.phylink_mac_config	= sja1105_mac_config,
> > 
> > Deleting sja1105_mac_config() here is safe not because
> > phylink_mac_config() stops calling pl->mac_ops->mac_config(), but
> > because dsa_port_phylink_mac_config() first checks whether
> > ds->ops->phylink_mac_config is implemented, and that is purely an
> > artefact of providing a phylib-style ds->ops->adjust_link, right?
> 
> Yes and no.
> 
> We already have a several DSA drivers that have NULL phylink_mac_config
> and that don't provide an adjust_link function. Even if adjust_link was
> eventually killed off, the test in dsa_port_phylink_mac_config() would
> still be necessary unless all these DSA drivers are updated with a stub
> function for it.
> 
> Consequently, I view phylink_mac_config in DSA as entirely optional and
> that optionality is already very much a part of the DSA interface, even
> though that is not the case with the corresponding phylink_mac_ops
> .mac_config method.
> 
> Moreover, this optionality is a common theme in DSA switch operations
> methods.
> 
> > Maybe it's worth mentioning.
> 
> Given that .phylink_mac_config is already established as being optional
> in DSA, does the addition of one more instance need to be explicitly
> mentioned?

I am aware of that, I am just pointing out that this is an unintended
side effect of the existence of adjust_link, and non-DSA phylink drivers
still need the mac_config stub. When going back and forth between a DSA
and a non-DSA driver, this is not obvious until you take into account
the dsa_port_phylink_mac_config() trampoline. Anyway, don't mention it
if you don't think it is necessary.