linux-kernel - RE: [PATCH net-next] r8169: add quirk for RTL8116af SerDes

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Message-ID: <c8bf99d9c3fc49958bad7f66863f72c2@realtek.com>
Date: Thu, 17 Jul 2025 17:45:13 +0000
From: Hau <hau@...ltek.com>
To: Andrew Lunn <andrew@...n.ch>
CC: "hkallweit1@...il.com" <hkallweit1@...il.com>,
        nic_swsd
	<nic_swsd@...ltek.com>,
        "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com"
	<edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next] r8169: add quirk for RTL8116af SerDes

> On Mon, Jul 14, 2025 at 03:28:37PM +0000, Hau wrote:
> > >
> > > Can you give us a few more details. What is on the other end of the
> SERDES?
> > > An SGMII PHY? An SFP cage? An Ethernet switch chip?
> > >
> > > A quick search suggests it is used with an SFP cage. How is the I2C
> > > bus connected? What about GPIOs? Does the RTL8116af itself have
> > > GPIOs and an I2C bus?
> > >
> 
> > RTL8116af 's SERDES will connect to a SFP cage. It has GPIO and a I2C
> > bus. But driver did not use it to access SFP cage.  Driver depends on
> > mac io 0x6c (LinkStatus) to check link status.
> 
> You cannot correctly use an SFP cage without using the I2C bus and the
> GPIOs. e.g. A copper SFP module likely needs SGMII, where as a fibre
> module needs 1000BaseX. You need to reprogram the PCS depending on
> what the SFP EEPROM says.
> 
> The kernel has all the code needed to coordinate this, phylink. All you need
> to do is write a standard Linux I2C bus driver, a standard Linux GPIO driver,
> and turn your PCS into a Linux PCS. You can then instantiate an SFP device.
> The txgbe driver does this, you can probably copy the code from there.
> 
> Have you licensed these parts? The txgbe hardware uses synopsys I2C and
> PCS. So all that was needed was a wrapper around the existing drivers.
> 
Thanks for your advice. I will check this internally to see if we can do this on device.

Thanks.