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Date:   Wed, 24 May 2023 20:35:10 +0300
From:   Vladimir Oltean <olteanv@gmail.com>
To:     arinc9.unal@gmail.com
Cc:     Sean Wang <sean.wang@mediatek.com>,
        Landen Chao <Landen.Chao@mediatek.com>,
        DENG Qingfang <dqfext@gmail.com>,
        Daniel Golle <daniel@makrotopia.org>,
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        Florian Fainelli <f.fainelli@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Russell King <linux@armlinux.org.uk>,
        =?utf-8?B?QXLEsW7DpyDDnE5BTA==?= <arinc.unal@arinc9.com>,
        Richard van Schagen <richard@routerhints.com>,
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        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
Subject: Re: [PATCH net-next 06/30] net: dsa: mt7530: improve code path for
 setting up port 5
Message-ID: <20230524173510.xvq434ekaee4664m@skbuf>
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On Mon, May 22, 2023 at 03:15:08PM +0300, arinc9.unal@gmail.com wrote:
> From: Arınç ÜNAL <arinc.unal@arinc9.com>
> 
> 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.