Public bug reported: Summary
MediaTek MT7925 (mt7925e, PCI 0000:09:00.0, ASIC revision 79250000) intermittently fails the mac80211 HT capability check at association time, logging: wlp9s0: required MCSes not supported, disabling HT immediately (~0.15s) before the corresponding associated line. The resulting link runs at 54 Mbit/s legacy (802.11a) rates instead of the negotiated HE rates. When association succeeds, the same card/AP pair negotiates 160MHz HE-MCS 9 NSS 2 (~1.9 Gbit/s rx). 35 occurrences were logged in a single boot session during one day of testing. Failure rate drifted from intermittent early in the day to nearly 100% of association attempts later the same day, with no software changes between good and bad periods. Environment Ubuntu 26.04 (Resolute), GNOME 50, Wayland Kernels tested: 7.0.0-28-generic and 7.0.0-29-generic — both affected linux-firmware-mediatek tested: 20260319.git217ca6e4-0ubuntu1 and 20260319.git217ca6e4-0ubuntu1.2 — both affected (WM firmware builds 20260106153007a and 20260605184651a respectively, confirmed via dmesg HW/SW Version lines) Card: MediaTek MT7925 (mt7925e driver), combo WiFi/BT AP: Xfinity gateway (XB-series), WPA2/WPA3 (PSK+SAE), 5GHz, 80MHz, 802.11ax; SSID also broadcast on 2.4GHz and 6GHz radios Regulatory domain: US (DFS-FCC), correctly set (verified with iw reg get) Connection profile pinned to the 5GHz BSSID with 802-11-wireless.band a (rules out band roaming as a factor; failures occur on direct association to the pinned 5GHz BSS) Evidence the failure is driver-local (not AP, config, or RF) The AP's over-the-air IEs are complete and identical in both frame types. Directed active scan (probe responses) and passive scan (beacons only) on the affected BSS both show: HT capabilities: 0x1ef, HT RX MCS rate indexes supported: 0-76 Full VHT RX/TX MCS sets (MCS 0-9, 4 streams) HE capabilities with Basic HE-MCS NSS Set: 0xfffc (i.e., only MCS 0-7 required for 1 stream) The card registers full local capabilities. iw phy shows HT TX/RX MCS rate indexes 0-15, HE MCS 0-11 on 2 streams, and EHT-MCS maps, on all bands. The mac80211 check that fails compares (1) against (2). The AP requires only MCS 0-7; the card supports MCS 0-15. This check cannot legitimately fail — its intermittent failure implies the driver's locally registered capability state is transiently invalid at association time. Other clients are unaffected. A phone concurrently sustains ~400 Mbit/s on the same 5GHz BSS while the mt7925e associates at 54 Mbit/s. Ruled out by testing: Full power-drain cold boots of the PC (multiple) AP reboot (full power cycle) PCIe device remove + rescan (echo 1 > .../remove, rescan) — fresh firmware download confirmed, error persists BSSID pinning, band restriction (band a), and channel restriction — error persists on direct cold associations Both kernel versions listed above Both firmware versions listed above Regulatory domain (correctly US) AP-side beacon/probe-response corruption (see point 1) Steps to reproduce Associate with an 802.11ax AP: nmcli connection down <ssid> && nmcli connection up <ssid> Check the kernel log: journalctl -k -b | grep 'required MCSes' When the bug triggers, the error line appears ~0.15s before that association's associated line, and iw dev wlp9s0 station dump shows 54 Mbit/s legacy rates with no MCS notation. When it does not trigger, the link reports e.g. rx bitrate: 1921.5 MBit/s 160MHz HE-MCS 9 HE-NSS 2. Repeating step 1 in a loop reproduces the failure on most or all iterations during bad periods (4 consecutive cold associations all failed in one test loop; timestamps in attached logs). Partial workarounds (unreliable) A full broadcast rescan immediately before connecting (nmcli dev wifi rescan; sleep 5; nmcli connection up <ssid>) initially yielded clean associations 4/4, but the same procedure later the same day failed 6/6. modprobe -r mt7925e && modprobe mt7925e followed by re-association sometimes yields a clean association; also degraded to 0% success later in the day. No deterministic workaround found. Example log excerpt [ 4865.392517] wlp9s0: required MCSes not supported, disabling HT [ 4865.4xxxxx] wlp9s0: authenticate with <bssid> ... [ 4865.4xxxxx] wlp9s0: authenticated [ 4865.4xxxxx] wlp9s0: associate with <bssid> (try 1/3) [ 4865.4xxxxx] wlp9s0: RX AssocResp from <bssid> (capab=0x1811 status=0 aid=NN) [ 4865.4xxxxx] wlp9s0: associated (Association is accepted by the AP with status=0; the link is simply crippled to legacy rates because HT/VHT/HE were disabled locally.) Attachments to include journalctl -k -b > kernel-log.txt iw phy > iw-phy.txt sudo iw dev wlp9s0 scan freq 5785 ssid <ssid> > scan-active.txt sudo iw dev wlp9s0 scan freq 5785 passive > scan-passive.txt lspci -vv -s 09:00.0 > lspci.txt sudo dmesg | grep -i mt7925 > mt7925-init.txt Optional parallel report The mt76 maintainers triage upstream issues at https://github.com/openwrt/mt76/issues — the same text works there. If you file both, cross-link them so whichever side picks it up first sees the other. ProblemType: Bug DistroRelease: Ubuntu 26.04 Package: linux-image-7.0.0-28-generic 7.0.0-28.28 ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12 Uname: Linux 7.0.0-28-generic x86_64 ApportVersion: 2.34.1-0ubuntu0.1 Architecture: amd64 CasperMD5CheckResult: pass CurrentDesktop: ubuntu:GNOME Date: Fri Aug 7 17:05:48 2026 InstallationDate: Installed on 2026-04-27 (103 days ago) InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1) MachineType: ASUS System Product Name ProcEnviron: LANG=en_US.UTF-8 PATH=(custom, no user) SHELL=/bin/bash TERM=xterm-256color XDG_RUNTIME_DIR=<set> ProcFB: 0 nvidia-drmdrmfb ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-28-generic root=UUID=220227b6-6e16-48a9-9799-c30fd7eb996d ro quiet splash crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon. SourcePackage: linux UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 04/09/2026 dmi.bios.release: 22.2 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: 2202 dmi.board.asset.tag: Default string dmi.board.name: ROG STRIX X870E-E GAMING WIFI7 R2 dmi.board.vendor: ASUSTeK COMPUTER INC. dmi.board.version: Rev 1.xx dmi.chassis.asset.tag: Default string dmi.chassis.type: 3 dmi.chassis.vendor: Default string dmi.chassis.version: Default string dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2202:bd04/09/2026:br22.2:svnASUS:pnSystemProductName:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnROGSTRIXX870E-EGAMINGWIFI7R2:rvrRev1.xx:cvnDefaultstring:ct3:cvrDefaultstring:skuSKU:pfaTobefilledbyO.E.M.: dmi.product.family: To be filled by O.E.M. dmi.product.name: System Product Name dmi.product.sku: SKU dmi.product.version: System Version dmi.sys.vendor: ASUS ** Affects: linux (Ubuntu) Importance: Undecided Status: New ** Tags: amd64 apport-bug resolute wayland-session -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2163073 Title: mt7925e: intermittent "required MCSes not supported, disabling HT" on association — link stuck at 54 Mbit/s legacy rates (35 occurrences in one boot) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2163073/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
