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

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Message-ID: <94e3d09a-e6a4-4808-bc29-3f494b65e170@gmail.com>
Date: Fri, 15 Mar 2024 10:26:41 -0700
From: Florian Fainelli <f.fainelli@...il.com>
To: arinc.unal@...nc9.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 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.

LGTM otherwise!
-- 
Florian