linux-kernel - Re: [PATCH net-next v2] net: dsa: mt7530: detect PHY muxing when PHY is defined on switch MDIO bus

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Date: Tue, 7 May 2024 10:25:57 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: Daniel Golle <daniel@...rotopia.org>
Cc: 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>,
 Bartel Eerdekens <bartel.eerdekens@...stell8.be>, mithat.guner@...ont.com,
 erkin.bozoglu@...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 v2] net: dsa: mt7530: detect PHY muxing when PHY
 is defined on switch MDIO bus

On 06/05/2024 14:24, Daniel Golle wrote:
> On Tue, Apr 30, 2024 at 08:01:33AM +0300, Arınç ÜNAL via B4 Relay wrote:
>> From: Arınç ÜNAL <arinc.unal@...nc9.com>
>>
>> Currently, the MT7530 DSA subdriver configures the MT7530 switch to provide
>> direct access to switch PHYs, meaning, the switch PHYs listen on the MDIO
>> bus the switch listens on. The PHY muxing feature makes use of this.
>>
>> This is problematic as the PHY may be attached before the switch is
>> initialised, in which case, the PHY will fail to be attached.
>>
>> Since commit 91374ba537bd ("net: dsa: mt7530: support OF-based registration
>> of switch MDIO bus"), we can describe the switch PHYs on the MDIO bus of
>> the switch on the device tree. Extend the check to detect PHY muxing when
>> the PHY is defined on the MDIO bus of the switch on the device tree.
>>
>> When the PHY is described this way, the switch will be initialised first,
>> then the switch MDIO bus will be registered. Only after these steps, the
>> PHY will be attached.
>>
>> Signed-off-by: Arınç ÜNAL <arinc.unal@...nc9.com>
> 
> Reviewed-by: Daniel Golle <daniel@...rotopia.org>
> 
>> ---
>> Changes in v2:
>> - Address the terminology on the patch log.
>> - Link to v1: https://lore.kernel.org/r/20240429-b4-for-netnext-mt7530-use-switch-mdio-bus-for-phy-muxing-v1-1-1f775983e155@arinc9.com
>> ---
>>   drivers/net/dsa/mt7530.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
>> index 2b9f904a98f0..6cf21c9d523b 100644
>> --- a/drivers/net/dsa/mt7530.c
>> +++ b/drivers/net/dsa/mt7530.c
>> @@ -2483,7 +2483,8 @@ mt7530_setup(struct dsa_switch *ds)
>>   			if (!phy_node)
>>   				continue;
>>   
>> -			if (phy_node->parent == priv->dev->of_node->parent) {
>> +			if (phy_node->parent == priv->dev->of_node->parent ||
>> +			    phy_node->parent->parent == priv->dev->of_node) {
> 
> I had some concerns about missing check for phy_node->parent != NULL,
> but it's impossible in practise. If phy_node exists, it will have a parent
> node as well.
> 
> To be super extra safe, maybe doing
> phy_node->parent && phy_node->parent->parent == priv->dev->of_node
> would be better.

At the current state of this driver where the hardware probes on OF, I
don't see any benefit of doing this so I'm going to pass on this for now.

Arınç