[Bug 2138308] Re: Ubuntu 25.10: 5GHz WiFi not detected with kernel 6.17/6.18 - Snapdragon X Elite

[Saikiran]

Investigation update:

I want to document the investigation steps taken so far to clarify the
root cause of the 5 GHz Wi-Fi failure.

Initially, based on timing and symptoms, I suspected an ASPM-related ath12k kernel regression. In particular, this commit was considered as a possible cause:
https://gitlab.com/Linaro/arm64-laptops/linux/-/commit/e9cf6413e6a80669b866b2d9a64dd4e4222fb77e

("wifi: ath12k: Use pci_{enable/disable}_link_state() APIs to
enable/disable ASPM states")

To verify this hypothesis, I checked whether the symbols introduced by
that commit were actually present and built into the kernel being
tested. I did this by searching the running kernel image for the
relevant symbols (pci_enable_link_state / pci_disable_link_state). No
matching symbols were found, confirming that this commit was not
included in the affected kernel.

Since the 5 GHz failure occurs even when this commit is not present,
this ASPM hypothesis can be ruled out.

After ruling this out, I reviewed commit history between a working kernel (6.16, July 2025) and broken kernels (6.17+). During this review, I identified commits that significantly changed how ath12k firmware statistics are handled, most notably:
bd6ec81 ("wifi: ath12k: Make firmware stats reset caller-driven")
2977567 ("wifi: ath12k: Fix timeout error during beacon stats retrieval")

These commits changed the behavior of ath12k_fw_stats_reset(), removing
automatic resets and requiring callers to explicitly manage firmware
stats buffer state.

On broken kernels, the failure consistently manifests as:
"failed to pull fw stats: -71"
followed immediately by scan abort / scan start failure messages.

Additional observations:
The same firmware version (WLAN.HMT.1.1.c5-00302) works correctly on kernel 6.16 but fails on 6.17+.
2.4 GHz scanning works, but 5 GHz scanning fails.
iw phy reports correct 5 GHz capabilities and the regulatory database loads correctly.
Error -71 (EPROTO) suggests a firmware–driver communication failure rather than a regulatory or hardware issue.

Based on this, the current working hypothesis is that driver-side
changes in firmware statistics handling introduced a state, timing, or
buffer management issue that affects firmware interaction during 5 GHz
scan preparation. The 5 GHz scan path requires additional firmware stats
/ TX power queries that are not exercised in the 2.4 GHz path.

This does not appear to be an ASPM regression, a hardware detection
issue, or a regulatory database issue. The bug remains valid and
reproducible, and currently appears to involve firmware–driver
compatibility with newer kernels rather than a single kernel regression.

Next steps are to test with the firmware stats commits reverted, add
targeted debug logging around firmware stats handling, and further
narrow down the exact interaction causing the firmware to reject 5 GHz
scan start requests.

TL;DR: ASPM regression ruled out; same firmware works on 6.16 but fails
on 6.17+, pointing to an ath12k firmware–driver interaction issue
(likely firmware stats handling) that breaks 5 GHz scans only.

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https://bugs.launchpad.net/bugs/2138308

Title:
  Ubuntu 25.10: 5GHz WiFi not detected with kernel 6.17/6.18 -
  Snapdragon X Elite

Status in ubuntu-concept:
  New

Bug description:
  This is a regression affecting ath12k on Qualcomm WCN7850 (Snapdragon
  X Elite laptops).

  Hardware:
  - Lenovo Yoga Slim 7x (Snapdragon X Elite)
  - Wi-Fi chipset: Qualcomm WCN7850 (ath12k_pci, hw2.0)

  Kernel versions tested:
  - 6.16.0-21-qcom-x1e → WORKING (5 GHz detected and usable)
  - 6.17.x → BROKEN (no 5 GHz BSS detected)
  - 6.18.0-9-qcom-x1e  → BROKEN (no 5 GHz BSS detected)

  Expected result:
  5 GHz networks should be detected and connectable, as on kernel 6.16.

  Actual result on 6.18:
  - No 5 GHz BSS entries appear at all
  - iw dev <iface> scan shows only 2.4 GHz channels (1–13)
  - This happens with:
    - ISP GPON router (non-DFS, channel 36, WPA2)
    - Samsung Galaxy S25+ hotspot forced to 5 GHz
  - NetworkManager never sees any 5 GHz SSIDs because the kernel scan does not report them.

  Debugging already performed:
  - ath12k firmware loads successfully
  - No firmware load failures
  - Regulatory domain correctly set (IN)
  - Disabled ath12k fw_stats polling (to fix earlier timeouts)
  - Disabled 802.11ax in cfg80211 (no effect)
  - Issue persists even after clean initramfs rebuild and reboot
  - No ath12k errors are logged on 6.18; 5 GHz frames appear to be
    dropped before BSS creation

  Additional evidence:
  - Same hardware, same firmware, same router
  - Only kernel version change causes regression

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