netdev - Re: Quirks for exotic SFP module

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Message-ID: <561dff8e-8a12-4f99-86e2-b5cdc8632d4a@lunn.ch>
Date: Sat, 6 May 2023 15:35:42 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Lorenz Brun <lorenz@...n.one>
Cc: netdev@...r.kernel.org, Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: Quirks for exotic SFP module

> Oh, so you're talking about signalling on the AR8033 <-> Linux Host part of
> the link. I actually wasn't aware that 1000Base-X did in-band signalling,
> TIL. Since the I2C bus is connected to the modem SoC it would have to
> forward any MDIO to the AR8033 transceiver, right? This would also be a bit
> weird as the AR8033 is connected "backwards", i.e. with RGMII facing towards
> the Modem SoC and 1000Base-X towards the Linux host.

I2C allows for there to be multiple devices on the bus. So a PHY which
supports I2C could be placed on the bus along side the SoC
implementing the modem.

However, Russell indicated that the Atheros PHY does not have native
I2C. So it is unlikely to be on the bus. This is probably why the
Marvell PHY is used a lot, not many PHYs do have I2C.

	Andrew