[Bug 2143056] Re: ath12k/WCN7850 (FastConnect 7800) 5GHz scan failure on kernel 6.17 -- works on 6.14

Hi Mark,

Thank you for your detailed report on the ath12k/WCN7850 5GHz scan
failure on kernel 6.17.

I've investigated this issue and can confirm it's a known upstream
regression affecting the Qualcomm FastConnect 7800 (WCN785x) Wi-Fi
adapter when using Linux kernel 6.17+. The problem stems from frequency
range filtering logic introduced in kernel 6.17 that breaks single-phy
devices like yours.

Good news: patches to fix this have been submitted to the linux-wireless mailing list by Saikiran B on January 23, 2026 and are currently under review. You can read the discussion here:
https://lore.kernel.org/linux-wireless/20260123155750.6007-1-bjsaikiran@gmail.com/T/#t

In the meantime, your workaround of using kernel 6.14.0-37-generic is
confirmed effective. Please continue using that kernel until an upstream
fix is merged and backported to Ubuntu's stable releases.

Thanks again for helping improve Ubuntu!

** Package changed: ubuntu => linux (Ubuntu)

** Changed in: linux (Ubuntu)
Status: New => Confirmed

--
You received this bug notification because you are subscribed to linux
in Ubuntu.
Matching subscriptions: Bgg, Bmail, Nb
https://bugs.launchpad.net/bugs/2143056

Title:
ath12k/WCN7850 (FastConnect 7800) 5GHz scan failure on kernel 6.17 --
works on 6.14

Status in linux package in Ubuntu:
Confirmed

Bug description:
On kernel 6.17.0-14-generic, the Qualcomm FastConnect 7800 (WCN7850) Wi-Fi adapter is completely unable to detect or connect to 5GHz networks. Only 2.4GHz networks are visible. The issue does not occur on kernel 6.14.0-37-generic, confirming this is a 6.17 regression.
Symptoms:

No 5GHz networks appear in scan results (nmcli dev wifi list / iwlist scan)
Repeated "received scan start failure event" in dmesg
Throughput dropped from ~600 Mbps (5GHz on 6.14) to ~60 Mbps (2.4GHz only on 6.17)
phy#0 self-manages regulatory domain, setting country 00 with all 5GHz channels as PASSIVE-SCAN only

Hardware:

Qualcomm WCN785x Wi-Fi 7 FastConnect 7800, PCI 0000:09:00.0 rev 01
Subsystem: Foxconn International
Firmware: WLAN.HMT.1.1.c5-00284.1, build 2025-05-17
Driver: ath12k_pci (compiled into kernel, not a module)

Kernel log (6.17 boot):
```
ath12k_pci 0000:09:00.0: received scan start failure event
ath12k_pci 0000:09:00.0: received scan start failure event
ath12k_pci 0000:09:00.0: received scan start failure event
ath12k_pci 0000:09:00.0: received scan start failure event
```

Additional notes:

No ath12k firmware packages were updated prior to the regression
ath12k on 6.17 only exposes debug_mask and ftm_mode module params — no regulatory override available
country_code and reg_proto_off params are silently ignored

Workaround: Booting kernel 6.14.0-37-generic fully resolves the issue.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2143056/+subscriptions