netdev - Re: [net-next PATCH 3/8] net: phy: Add 25G-CR, 50G-CR, 100G-CR2 support to C45 genphy

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Message-ID: <c06dc4a6-85b4-41e9-9060-06303f7bbdbc@bootlin.com>
Date: Tue, 28 Oct 2025 08:32:03 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Alexander Duyck <alexander.duyck@...il.com>, netdev@...r.kernel.org
Cc: kuba@...nel.org, kernel-team@...a.com, andrew+netdev@...n.ch,
 hkallweit1@...il.com, linux@...linux.org.uk, pabeni@...hat.com,
 davem@...emloft.net
Subject: Re: [net-next PATCH 3/8] net: phy: Add 25G-CR, 50G-CR, 100G-CR2
 support to C45 genphy

Hi Alexander,

On 24/10/2025 22:40, Alexander Duyck wrote:
> From: Alexander Duyck <alexanderduyck@...com>
> 
> Add support for 25G-CR, 50G-CR, 50G-CR2, and 100G-CR2 the c45 genphy. Note
> that 3 of the 4 are IEEE compliant so they are a direct copy from the
> clause 45 specification, the only exception to this is 50G-CR2 which is
> part of the Ethernet Consortium specification which never referenced how to
> handle this in the MDIO registers.
> 
> Since 50GBase-CR2 isn't an IEEE standard it doesn't have a value in the
> extended capabilities registers. To account for that I am adding a define
> that is aliasing the 100GBase-CR4 to represent it as that is the media type
> used to carry data for 50R2, it is just that the PHY is carrying two 2 with
> 2 lanes each over the 4 lane cable. For now I am representing it with ctrl1
> set to 50G and ctrl2 being set to 100R4, and using the 100R4 capability to
> identify if it is supported or not.I

If 50GBase-CR2 isn't part of IEEE standards and doesn't appear in the
C45 ext caps, does it really belong in a genphy helper ?

You should be able to support it through the .config_anef() callback in
the PHY driver. I'm absolutely not familiar with these high-speed interfaces,
so maybe this is very common...

Maxime