[REGRESSION] mt7925: MLO connectivity silently stalls with 6GHz link active

[Jonas Hort]

Hi all,

Friendly ping on this one - any news on the mt7925 MLO stall?

No pressure, I know everyone's busy. My setup is still in place, so
I'm happy to build and test patches or collect further traces if
that would help. Nothing has changed here: still reproducible with
the 5 GHz + 6 GHz pair.

Thanks for all the help so far.
Jonas

Am 30.08.26 um 00:13 schrieb Devin Wittmayer:
> On Mon, 2026-08-24 at 08:18 +0000, Jonas Hort wrote:
>> Setup is still up and I can build and test whatever is useful.
> Your bisect holds here, on a different machine and a different access
> point, running your June firmware. Three states, each replicated:
>
>    both commits reverted        clean, two runs of six minutes
>    only the later one reverted  stalls, two runs
>    neither reverted             stalls, three runs
>
> Tail welded and head climbing, which is your signature. The tree is
> 7.2-rc5 with one unrelated ACPI patch of mine, nowhere near this path.
>
> db134691924f lands fifteen commits after ff643b81bc38, and reverting it
> alone still stalls, so the builder rewrite is the one that matters.
> Reverting the builder on its own is not available either: v7.0's version
> dereferences a link pointer that the later commit leaves unpublished
> until after the firmware call, so it would need a check neither version
> has.
>
> A correction to my last message. I pointed you at the link count, since
> the new code reports one link whenever the update concerns the primary.
> That undercount is real but it's not the cause. Telling firmware one
> link always is clean over two six-minute runs. Skipping the
> undercounting update entirely, so firmware is never told anything wrong,
> stalls on both runs. Writing the entries in v7.0's order stalls on all
> three.
>
> On the August firmware, stock still stalls, twice, the detector firing
> 95 and 141 seconds into the run.
>
> The band pair matters. Same driver, same August firmware, two runs each:
>
>    5 GHz + 6 GHz     stalls
>    2.4 GHz + 5 GHz   clean, full duration
>    2.4 GHz + 6 GHz   clean, full duration
>
> Not the channel width. Narrowing the 5 GHz link to 40 MHz, so that pair
> carries the same narrow-plus-wide mix as the clean ones, still stalls on
> both runs.
>
> The sharpest pair there is the two runs where the iperf3 stream never
> established, leaving only the UDP pressure: 5 plus 6 stalled with the
> queue peaking at 187, and 2.4 plus 6 stayed clean at 186. The other
> three clean runs peaked above 1000.
>
> Sean, the two things I can't see from out here: what firmware does with
> a multi-link record naming one link while a second is associated, and
> why 5 plus 6 should differ from 2.4 plus 6.
>
> Jonas, thank you for the bisect. Five steps, every bad verdict confirmed
> on the queue signature.
>
> Devin