linux-kernel - Re: [PATCH 1/2] arm64: dts: mediatek: mt7622: set PHY address of MT7531 switch to 0x1f

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Message-ID: <62d128f1-11ac-4669-90ff-e9cdd0ec5bd9@arinc9.com>
Date: Sat, 16 Mar 2024 10:43:40 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: Florian Fainelli <f.fainelli@...il.com>, Rob Herring
 <robh+dt@...nel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>,
 Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: mithat.guner@...ont.com, erkin.bozoglu@...ont.com,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 1/2] arm64: dts: mediatek: mt7622: set PHY address of
 MT7531 switch to 0x1f

On 15.03.2024 20:26, Florian Fainelli wrote:
> On 3/14/24 05:20, Arınç ÜNAL via B4 Relay wrote:
>> From: Arınç ÜNAL <arinc.unal@...nc9.com>
>>
>> The MT7531 switch listens on PHY address 0x1f on an MDIO bus. I've got two
>> findings that support this. There's no bootstrapping option to change the
>> PHY address of the switch. The Linux driver hardcodes 0x1f as the PHY
>> address of the switch. So the reg property on the device tree is currently
>> ignored by the Linux driver.
>>
>> Therefore, describe the correct PHY address on boards that have this
>> switch.
> 
> Can we call it a pseudo PHY to use a similar terminology as what is done through drivers/net/dsa/{bcm_sf2,b53}*?
> 
> This is not a real PHY as in it has no actual transceiver/digital signal processing logic, this is a piece of logic that snoops for MDIO transactions at that specific address and lets you access the switch's internal register as if it was a MDIO device.

I can get behind calling the switch a psuedo-PHY in the context of MDIO.
However, as described on "22.2.4.5.5 PHYAD (PHY Address)" of "22.2.4.5
Management frame structure" of the active standard IEEE Std 802.3™‐2022,
the field is called "PHY Address". The patch log doesn't give an identifier
as to what a switch is in the context of MDIO. Only that it listens on a
certain PHY address which the term complies with IEEE Std 802.3™‐2022.

So I don't see an improvement to be made on the patch log. Feel free to
elaborate further.

Arınç