SFP ports stop working with Linux 6.14 in Arch Linux

Ten64 Forum
1

When upgrading my box today to the latest kernel, I found that I lost all connectivity on the SFP ports. When I rolled back to kernel version 6.13, they worked again.

On the bad kernel version, I do see these log lines:

Apr 10 19:20:05 Heimdall kernel: fsl_dpaa2_eth dpni.1 (unnamed net_device) (uninitialized): autoneg setting not compatible with PCS
Apr 10 19:20:05 Heimdall kernel: sfp dpmac2-sfp: Unable to ascertain link mode
Apr 10 19:20:05 Heimdall kernel: fsl_dpaa2_eth dpni.1 eth8: selection of interface failed, advertisement 00,00000000,00000000,00000000

When I have time, I’ll likely do a bisect to locate the exact commit if I can.

2

This appears to be due to a feature introduced in the 6.14 cycle, which deals with in-band negotiation (something generally used with <=1Gbps copper ports and SFPs)

https://patchwork.kernel.org/project/netdevbpf/cover/Z08kCwxdkU4n2V6x@shell.armlinux.org.uk/

And specifically this patch to the PCS driver used on this hardware (lynx):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.15-rc1&id=6561f0e547be221f411fda5eddfcc5bd8bb058a5

I have just tested reverting the above commit on the Linus tree and the SFPs work again.

I’ll do some more checking next week, before formally reporting it as a regression.

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