Fix MediaTek MT7921 / MT7922 slow Wi-Fi on Linux ("required MCSes not supported, disabling HT")

Wi-Fi connects but is stuck at ~10–20 Mbit/s on Linux, while Windows gets hundreds of Mbit/s to gigabit on the same laptop/desktop and same router. iw link shows 54.0 MBit/s / 20 MHz (no HT) and dmesg says required MCSes not supported, disabling HT. This repo fixes it.

TL;DR — If your MediaTek Wi-Fi card (MT7921 / MT7922 / MT7921e / MT7922e, driver mt7921e) connects fine but caps out around 10–20 Mbit/s on Linux while Windows gets hundreds of Mbit/s to gigabit on the same machine and router, and dmesg shows:

wlanX: required MCSes not supported, disabling HT

…then your kernel's mac80211 is refusing to use 802.11n/ac/ax (HT/VHT/HE) and dropping to legacy 54 Mbit/s. This repo patches mac80211 to skip that overly-strict check and restores full speed. Build is non-destructive and reversible.

On the machine this was written on (ASUS TUF GAMING B650E-E WIFI, MT7922, linux-zen):

	Before	After
iw link rate	54.0 MBit/s, 20 MHz, no HT	1200 MBit/s, 80 MHz, HE-MCS 11 NSS 2
speedtest-cli download	16 Mbit/s	~430 Mbit/s

---

Symptoms

• Wi-Fi associates and has internet, but download is a tiny fraction of your plan.
• Same computer dual-booting Windows gets full speed → not hardware, not the router.
• iw dev wlanX link shows a legacy rate and 20 MHz (no HT):

  rx bitrate: 54.0 MBit/s
  channel 157 (5785 MHz), width: 20 MHz (no HT)
  

• iw dev wlanX info may report a nonsense txpower 3.00 dBm (cosmetic on this driver — ignore it; it reads 3 dBm even at 1200 Mbit/s).
• The smoking gun, in sudo dmesg:

  wlanX: required MCSes not supported, disabling HT
  

• Reproduces on both 2.4 GHz and 5 GHz, on every AP, regardless of signal strength — because it's a client-side decision, not an RF problem.

Root cause

Early-2025 mac80211 added strict verification of the AP's Basic HT-MCS Set (the "required" MCS rates in the HT Operation IE), in ieee80211_verify_sta_ht_mcs_support() in net/mac80211/mlme.c.

Many 4×4 ISP gateways (Xfinity XB8, and others — the box this was debugged on is a Comcast-style gateway) advertise required MCS rates that need 3–4 spatial streams. A typical laptop/desktop card like the MT7922 is only 2×2 (HT MCS 0–15). Per the letter of the spec, mac80211 then decides the station "can't meet the basic rate set" and disables HT entirely, collapsing the link to 802.11a/g 54 Mbit/s.

Windows (and older Linux kernels) never enforced this, so they connect at full 2×2 speed — which is why Windows is fast and Linux is not. The basic-MCS set only governs management/broadcast expectations; a 2×2 station transmits its unicast data on the 2×2 rates it does support perfectly well, so skipping the check is safe in practice.

The fix

A one-hunk patch (skip-basic-mcs-check.patch) makes ieee80211_verify_sta_ht_mcs_support() return true early instead of disabling HT:

	if (!ht_op)
		return false;

+	/* Skip basic MCS set validation (4x4 AP + 2x2 STA). The STA still
+	 * works fine using its own supported rates for data transfer. */
+	return true;
	memcpy(&sta_ht_cap, &sband->ht_cap, sizeof(sta_ht_cap));

The patched mac80211.ko is built against your installed kernel headers and dropped into /usr/lib/modules/<ver>/updates/, which shadows the stock module without overwriting it. Reverting = delete that file + depmod.

Install (Arch / Arch-based)

git clone <this-repo> mt7922-ht-mcs-fix
cd mt7922-ht-mcs-fix
sudo ./install.sh

install.sh will:

1. ensure base-devel / bc are present,
2. install the rebuild helper to /usr/local/bin/rebuild-mac80211,
3. install a pacman hook so the module is rebuilt automatically after any linux / linux-zen / linux-lts / linux-hardened (+ -headers) upgrade,
4. build + install the patched module for every installed kernel that has headers.

Then activate without rebooting:

sudo modprobe -r mt7921e mt7921_common mt792x_lib mt76_connac_lib mt76
sudo modprobe -r mac80211
sudo modprobe mac80211 && sudo modprobe mt7921e

(or just reboot). Verify:

iw dev wlanX link    # expect '80MHz HE-MCS ...' instead of '54.0 MBit/s ... no HT'
speedtest-cli --simple

Revert

sudo ./uninstall.sh

Removes the hook, deletes the patched module from every kernel's updates/, runs depmod. Stock mac80211 returns on the next reload/reboot.

Other distributions (Fedora, Ubuntu/Debian, etc.)

Only install.sh, the pacman hook, and rebuild-mac80211.sh are Arch-specific. The patch itself is distro-agnostic — the bug is in the upstream kernel's mac80211. On any distro you can apply it manually:

# 1. install kernel build deps + headers for your *running* kernel
#    Fedora:  sudo dnf install kernel-devel-$(uname -r) gcc make bc
#    Debian/Ubuntu: sudo apt install linux-headers-$(uname -r) build-essential bc

# 2. grab matching upstream mac80211 source, patch, build, install
KVER=$(uname -r); BASE=${KVER%%-*}; MAJ=${BASE%%.*}
curl -fSLO https://cdn.kernel.org/pub/linux/kernel/v${MAJ}.x/linux-$BASE.tar.xz
tar xf linux-$BASE.tar.xz linux-$BASE/net/mac80211/
cd linux-$BASE && patch -p1 < /path/to/skip-basic-mcs-check.patch
make -C /lib/modules/$KVER/build M=$PWD/net/mac80211 modules
sudo cp net/mac80211/mac80211.ko /lib/modules/$KVER/updates/ && sudo depmod $KVER

# 3. reload (see below) or reboot

Notes & caveats

• The rebuilt module is out-of-tree tainted (OE in lsmod/dmesg). Harmless.
• The pacman hook builds for all installed kernels with headers, so if you keep linux-zen-headers (etc.) installed, kernel upgrades stay fixed. If a future kernel refactors mlme.c and the patch fails to apply, the hook errors out and you simply fall back to stock (slow) behavior — nothing breaks; just re-check the patch.
• This is a 2×2 station workaround. It does not "fake" rates — the card still only uses MCS it genuinely supports; it just stops mac80211 from throwing out HT/VHT/HE.
• Real upstream fix would be for mac80211 to not disable HT purely on a basic-MCS mismatch (or for ISP gateways to stop advertising 4-stream basic rates).

Tested on

• ASUS TUF GAMING B650E-E WIFI, MediaTek MT7922 (14c3:0616, mt7921e)
• linux-zen 7.0.10, linux-firmware-mediatek 20260519
• Comcast/Xfinity-style 4×4 gateway
• 16 Mbit/s → ~430 Mbit/s download

Credits & attribution

• The patch and the original DKMS/pacman-hook approach come from WoodyWoodster/mac80211-mcs-patch: https://github.com/WoodyWoodster/mac80211-mcs-patch. This repo reuses that patch verbatim and extends the tooling to handle non-default kernels (e.g. linux-zen) and to rebuild for all installed kernels.
• Arch Linux forum thread that surfaced the fix — "mt7921e: stuck at 54 Mbps max, on both 2.4 GHz and 5 GHz": https://bbs.archlinux.org/viewtopic.php?pid=2296485
• The mac80211 change that introduced the strict check — "wifi: mac80211: add HT and VHT basic set verification" (linux-wireless, Feb 2025): https://patchwork.kernel.org/project/linux-wireless/patch/20250204193721.7dfdeb1235bb.I66bcf6c2de3b9d3325e4ffd9f573f4cd26ce5685@changeid/

Keywords

For anyone searching: MediaTek MT7921 MT7922 MT7921e MT7922e MT7921K AzureWave slow wifi on Linux, wifi stuck at 54 Mbps / 54 Mbit/s, only getting 10-20 Mbps, fast on Windows slow on Linux, mt7921e low throughput, required MCSes not supported disabling HT, mac80211 disables HT/VHT/HE, no HT 20 MHz, iw link 54.0 MBit/s, Wi-Fi 6 / 802.11ax / 802.11ac running at 802.11a/g speeds, Xfinity / Comcast XB7 XB8 gateway 4x4 AP with 2x2 client, ASUS B650 / B650E / TUF / ROG onboard Wi-Fi, Framework / Lenovo / handheld MT7922 slow, Arch Linux linux-zen linux-lts, Fedora, Ubuntu, Debian.

License

The patch follows the Linux kernel's GPL-2.0. Scripts and docs here are released under GPL-2.0 as well.