[SRU][R][PATCH 0/1] Realtek RTL8116AF SFP option module fails to get connected

[AceLan Kao]

From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/2116144

[Impact]
LAN does not work when using Realtek RTL8116AF SFP option module. Network
interface stays down — no link, no connectivity. Hits 100% on affected
hardware.
RTL8116AF is a variant of RTL8168fp that uses SerDes instead of PHY for
link status. The r8169 driver reads PHY registers for link state, but
SerDes status is not reflected in those registers on RTL8116AF. The driver
sees no link even when the cable is connected and the SerDes link is up.

[Fix]
Add a quirk for RTL8116AF that reflects SerDes status during PHY register
reads. A detection function identifies RTL8116AF by MAC version and OCP
register values. When detected, the MDIO read path ORs in the SerDes link
status (BMSR and PHYSR registers) so the driver sees the correct link
state.
Patch from Realtek, posted to lkml, not merged upstream yet:
https://lore.kernel.org/lkml/20250711034412.17937-1-hau@realtek.com/

[Test Plan]
1. Connect transceiver and network cable to SFP option module with
   RTL8116AF chip.
2. Boot to OS.
3. Check link status:
   $ ip link show
Without patch: interface shows NO-CARRIER, no link detected.
With patch: interface shows link up, ping works.

[Where problems could occur]
Could break r8169 ethernet driver on RTL8168fp-based chips.
The detection function rtl_is_8116af() checks mac_version and two OCP
registers. If those register values match on a non-8116AF chip, the quirk
would OR wrong values into PHY reads. This could report a false link-up
or wrong speed on that chip.
The quirk also changes the MDIO read path for MAC versions
RTL_GIGA_MAC_VER_40 through RTL_GIGA_MAC_VER_LAST, so any future MAC
version that shares the same OCP register pattern would be affected.

[Other Info]
Realtek is preparing the next revision of this patch. The fix involves
architecture changes for fiber application, so the submission may happen
after May. That means we have to carry this SAUCE patch in the Resolute
kernel.

ChunHao Lin (1):
  UBUNTU: SAUCE: r8169: add quirk for RTL8116af SerDes

 drivers/net/ethernet/realtek/r8169_main.c | 40 ++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

-- 
2.53.0