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

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Date: Thu, 25 May 2023 09:42:39 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Sean Wang <sean.wang@...iatek.com>, Landen Chao
 <Landen.Chao@...iatek.com>, DENG Qingfang <dqfext@...il.com>,
 Daniel Golle <daniel@...rotopia.org>, Andrew Lunn <andrew@...n.ch>,
 Florian Fainelli <f.fainelli@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Russell King <linux@...linux.org.uk>,
 Richard van Schagen <richard@...terhints.com>,
 Richard van Schagen <vschagen@...com>,
 Frank Wunderlich <frank-w@...lic-files.de>,
 Bartel Eerdekens <bartel.eerdekens@...stell8.be>, erkin.bozoglu@...ont.com,
 mithat.guner@...ont.com, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next 06/30] net: dsa: mt7530: improve code path for
 setting up port 5

On 24.05.2023 20:35, Vladimir Oltean wrote:
> On Mon, May 22, 2023 at 03:15:08PM +0300, arinc9.unal@...il.com wrote:
>> From: Arınç ÜNAL <arinc.unal@...nc9.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.

True.

> 
> 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.

I will add this to the patch log:

This driver isn't in the dsa_switches_apply_workarounds[] array so 
phylink will always be present.

> 
>> 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.

Will do.

Arınç