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

[Saikiran]

I can confirm that 5GHz WiFi is fully functional on the Lenovo Yoga Slim
7x (Snapdragon X Elite) using kernel 6.19-rc5.

After extensively long testing (including testing just the regulatory
reverts, which failed), I have isolated the working configuration.

Attached is the complete series of 6 patches I am using.

The series is split into two parts:
1. Improvements & Cleanup (Patches 01-03)
2. Critical 5GHz Fixes (Patches 04-06)

It seems that Patch 06 (Remove broken frequency range filtering) is the
primary fix that actually enables 5GHz connectivity, as the system
remained broken with only patches 01-05 applied.

Patch Layout:
01-stats-leak.patch (Fixes a firmware stats leak)
02-fallback-domain.patch (Adds fallback reg domain support)
03-init-ranges.patch (Initializes regulatory freq ranges properly)
04-sync-reg.patch (Restores synchronous regulatory updates)
05-revert-faux.patch (Reverts faux_device to platform_device)
06-remove-broken-filtering.patch (The Critical Fix: Removes the broken logic)

Please consider merging.

** Attachment added: "Patch series (6 patches) fixing ath12k 5GHz WiFi on Snapdragon X Elite (Lenovo Yoga Slim 7x)."
   https://bugs.launchpad.net/ubuntu-concept/+bug/2138308/+attachment/5940008/+files/wifi-fixes.zip

** Tags removed: wlan
** Tags added: ath12k patch regression wifi

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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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