Re: [PATCH net-next 06/30] net: dsa: mt7530: improve code path for setting up port 5

[Vladimir Oltean]

On Mon, May 22, 2023 at 03:15:08PM +0300, arinc9.unal@xxxxxxxxx wrote:
> From: Arınç ÜNAL <arinc.unal@xxxxxxxxxx>
> 
> There're two code paths for setting up port 5:
> 
> mt7530_setup()
> -> mt7530_setup_port5()
> 
> mt753x_phylink_mac_config()
> -> mt753x_mac_config()
>    -> mt7530_mac_config()
>       -> mt7530_setup_port5()
> 
> Currently mt7530_setup_port5() from mt7530_setup() always runs. If port 5
> is used as a CPU, DSA, or user port, mt7530_setup_port5() from
> mt753x_phylink_mac_config() won't run. That is because priv->p5_interface
> set on mt7530_setup_port5() will match state->interface on
> mt753x_phylink_mac_config() which will stop running mt7530_setup_port5()
> again.
> 
> mt7530_setup_port5() from mt753x_phylink_mac_config() won't run when port 5
> is disabled or used for PHY muxing as port 5 won't be defined on the
> devicetree.
> 
> Therefore, mt7530_setup_port5() will never run from
> mt753x_phylink_mac_config().
> 
> Address this by not running mt7530_setup_port5() from mt7530_setup() if
> port 5 is used as a CPU, DSA, or user port. For the cases of PHY muxing or
> the port being disabled, call mt7530_setup_port5() from mt7530_setup().

So TL;DR: mt7530_setup() -> mt7530_setup_port5() short-circuits
mt753x_phylink_mac_config() -> ... -> mt7530_setup_port5() through the
stateful variable priv->p5_interface, such that port 5 is effectively
never configured by phylink, but statically at probe time. The main goal of
the patch is to undo the short-circuit, and let phylink configure port 5.

It is worth stating that we know phylink will always be present, because
mt7530 isn't in the dsa_switches_apply_workarounds[] array. Otherwise
this strategy would have been problematic with some device trees.

> Do not set priv->p5_interface on mt7530_setup_port5(). There won't be a
> case where mt753x_phylink_mac_config() runs after mt7530_setup_port5()
> anymore.

The bulk of the change is difficult enough to follow. I believe this
part could be done through a separate patch, and the rest would still
work.