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Message-ID: <CAN9vWDJvD9TZAwKUu8NSfbLZTLkNga8AR7LQ4qTTwEDxLr8brw@mail.gmail.com> Date: Sun, 16 Nov 2025 10:13:15 +0100 From: Michael Zimmermann <sigmaepsilon92@...il.com> To: Heiner Kallweit <hkallweit1@...il.com> Cc: nic_swsd@...ltek.com, 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>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: RTL8127AF doesn't get a link over SFP+ DAC On Thu, Nov 13, 2025 at 8:54 PM Heiner Kallweit <hkallweit1@...il.com> wrote: > > On 11/13/2025 6:30 PM, Michael Zimmermann wrote: > > Hi, > > > > I have a RT8127AF card from DIEWU: > > https://24wireless.info/diewu-txa403-and-txa405 . > > The card is detected just fine: > > [125201.683763] r8169 0000:08:00.0 eth1: RTL8127A, xx:xx:xx:xx:xx:xx, > > XID 6c9, IRQ 143 > > [125201.683770] r8169 0000:08:00.0 eth1: jumbo features [frames: 16362 > > bytes, tx checksumming: ko] > > [125201.688543] r8169 0000:08:00.0 enp8s0: renamed from eth1 > > [125201.715519] Realtek Internal NBASE-T PHY r8169-0-800:00: attached > > PHY driver (mii_bus:phy_addr=r8169-0-800:00, irq=MAC) > > [125202.277034] r8169 0000:08:00.0 enp8s0: Link is Down > > > > This is what ethtool shows: > > Settings for enp8s0: > > Supported ports: [ TP MII ] > > Supported link modes: 10baseT/Half 10baseT/Full > > 100baseT/Half 100baseT/Full > > 1000baseT/Full > > 10000baseT/Full > > 2500baseT/Full > > 5000baseT/Full > > Supported pause frame use: Symmetric Receive-only > > Supports auto-negotiation: Yes > > Supported FEC modes: Not reported > > Advertised link modes: 10baseT/Half 10baseT/Full > > 100baseT/Half 100baseT/Full > > 1000baseT/Full > > 10000baseT/Full > > 2500baseT/Full > > 5000baseT/Full > > Advertised pause frame use: Symmetric Receive-only > > Advertised auto-negotiation: Yes > > Advertised FEC modes: Not reported > > Speed: Unknown! > > Duplex: Unknown! (255) > > Auto-negotiation: on > > master-slave cfg: preferred slave > > master-slave status: unknown > > Port: Twisted Pair > > PHYAD: 0 > > Transceiver: internal > > MDI-X: Unknown > > Supports Wake-on: pumbg > > Wake-on: d > > Link detected: no > > > > and `ip a`: > > 10: enp8s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc > > fq_codel state DOWN group default qlen 1000 > > link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff > > altname enxXXXXXXXXXXXX > > > > And that's it, the link never comes up. The 10G Mikrotik switch on the > > other side sees that the module is inserted on its side, but doesn't > > show any change when I plug in the RTL8127AF. > > > > It works in Windows 11 and it also works with the r8127 Linux driver > > downloaded from Realteks website: > > https://www.realtek.com/Download/List?cate_id=584 : > > > > [129318.976134] r8127: This product is covered by one or more of the > > following patents: US6,570,884, US6,115,776, and US6,327,625. > > [129318.976175] r8127 Copyright (C) 2025 Realtek NIC software team > > <nicfae@...ltek.com> > > This program comes with ABSOLUTELY NO WARRANTY; for > > details, please see <http://www.gnu.org/licenses/>. > > This is free software, and you are welcome to > > redistribute it under certain conditions; see > > <http://www.gnu.org/licenses/>. > > [129318.988293] r8127 0000:08:00.0 enp8s0: renamed from eth1 > > [129318.997092] enp8s0: 0xffffd49ec9140000, xx:xx:xx:xx:xx:xx, IRQ 137 > > [129319.421629] r8127: enp8s0: link up > > > > ethtool with realteks driver shows something quite interesting: > > Settings for enp8s0: > > Supported ports: [ TP ] > > Supported link modes: 1000baseT/Full > > 10000baseT/Full > > Supported pause frame use: No > > Supports auto-negotiation: No > > Supported FEC modes: Not reported > > Advertised link modes: 1000baseT/Full > > 10000baseT/Full > > Advertised pause frame use: No > > Advertised auto-negotiation: No > > Advertised FEC modes: Not reported > > Speed: 10000Mb/s > > Duplex: Full > > Auto-negotiation: off > > Port: Twisted Pair > > PHYAD: 0 > > Transceiver: internal > > MDI-X: on > > Supports Wake-on: pumbg > > Wake-on: g > > Current message level: 0x00000033 (51) > > drv probe ifdown ifup > > Link detected: yes > > > > auto-negotiation is off, even though it's enabled on my Mikrotik > > switch. "ethtool -s enp8s0 autoneg on" (or off) on the realtek driver > > succeeds but doesn't change what ethtools status shows. "ethtool -s > > enp8s0 autoneg off" on the mainline driver does fail with: > > netlink error: link settings update failed > > netlink error: Invalid argument > > > > So while I have no idea why things are not working, my best theory is > > that auto-negotiation isn't supported (properly) and the mainline > > driver doesn't support disabling it. > > > Realtek uses a proprietary way to deal with the SFP and hides it > behind the internal PHY. The SFP signals aren't exposed. > When in fiber mode the internal PHY doesn't behave fully compliant > with clause 22 any longer. E.g. link status isn't reported by the > PHY, but only via a proprietary register. > To cut a long story short: Fiber mode isn't supported by r8169 > at the moment. > > > Thanks > > Michael > Thanks for the hint. I've spent some time understanding and comparing both drivers and testing a couple of things and was actually able to get it working with r8169. After some more testing and code cleanup I'll send a patch.
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