netdev - Re: [PATCH netnext 8/8] net: dsa: mt7530: simplify link operations and force link down on all ports

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Date: Fri, 16 Feb 2024 20:23:01 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Daniel Golle <daniel@...rotopia.org>, DENG Qingfang <dqfext@...il.com>,
 Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
 Florian Fainelli <f.fainelli@...il.com>, Vladimir Oltean
 <olteanv@...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>,
 mithat.guner@...ont.com, erkin.bozoglu@...ont.com,
 Bartel Eerdekens <bartel.eerdekens@...stell8.be>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH netnext 8/8] net: dsa: mt7530: simplify link operations
 and force link down on all ports

On 16.02.2024 18:43, Russell King (Oracle) wrote:
> On Thu, Feb 08, 2024 at 08:51:36AM +0300, Arınç ÜNAL via B4 Relay wrote:
>> From: Arınç ÜNAL <arinc.unal@...nc9.com>
>>
>> Currently, the link operations for switch MACs are scattered across
>> port_enable, port_disable, phylink_mac_config, phylink_mac_link_up, and
>> phylink_mac_link_down.
>>
>> port_enable and port_disable clears the link settings. Move that to
>> mt7530_setup() and mt7531_setup_common() which set up the switches. This
>> way, the link settings are cleared on all ports at setup, and then only
>> once with phylink_mac_link_down() when a link goes down.
>>
>> Enable force mode at setup to apply the force part of the link settings.
>> This ensures that only active ports will have their link up.
> 
> I think we may have a different interpretation of what phylink's
> mac_link_down() and mac_link_up() are supposed to be doing here.
> Of course, you have read the documentation of these methods so are
> fully aware of what they're supposed to do. So you are aware that
> when inband mode is being used, forcing the link down may be
> counter-productive depending on how the hardware works.

No, I haven't read the documentation [1] until your response here. My patch
here doesn't touch mt753x_phylink_mac_link_down(), it is already the case
with the driver that falls short of not forcing link down when inband mode
is being used.

That said, what I explain on the patch log does not properly describe the
driver behaviour. This should explain it correctly:

Enable force mode at setup to apply the force part of the link settings.
This ensures that the ports that were never active will have their link
down.

I could, in the future, study this thoroughly to make the driver fully
conform to the documentation.

[1] https://docs.kernel.org/networking/kapi.html#phylink

Arınç