linux-kernel - Re: [PATCH 3/3] net: j2: Introduce J-Core EMAC

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Message-ID: <9eab7a4ff3a72117a1a832b87425130f@artur-rojek.eu>
Date: Sat, 16 Aug 2025 15:40:57 +0200
From: Artur Rojek <contact@...ur-rojek.eu>
To: Andrew Lunn <andrew@...n.ch>
Cc: Rob Landley <rob@...dley.net>, Jeff Dionne <jeff@...esemi.io>, John Paul
 Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, Geert Uytterhoeven
 <geert+renesas@...der.be>, Andrew Lunn <andrew+netdev@...n.ch>, "David S .
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, netdev@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] net: j2: Introduce J-Core EMAC

On 2025-08-16 02:18, Andrew Lunn wrote:
>> Yes, it's an IC+ IP101ALF 10/100 Ethernet PHY [1]. It does have both 
>> MDC
>> and MDIO pins connected, however I suspect that nothing really
>> configures it, and it simply runs on default register values (which
>> allow for valid operation in 100Mb/s mode, it seems). I doubt there is
>> another IP core to handle MDIO, as this SoC design is optimized for
>> minimal utilization of FPGA blocks. Does it make sense to you that a 
>> MAC
>> could run without any access to an MDIO bus?
> 
> It can work like that. You will likely have problems if the link ever
> negotiates 10Mbps or 100Mbps half duplex. You generally need to change
> something in the MAC to support different speeds and duplex. Without
> being able to talk to the PHY over MDIO you have no idea what it has
> negotiated with the link peer.

Thanks for the explanation. I just confirmed that there is no activity
on the MDIO bus from board power on, up to the jcore_emac driver start
(and past it), so most likely this SoC design does not provide any
management interface between MAC and PHY. I guess once/if MDIO is
implemented, we can distinguish between IP core revision compatibles,
and properly switch between netif_carrier_*()/phylink logic.

Cheers,
Artur

> 
> 	Andrew