Re: mac80211: HT disabled ("required MCSes not supported") on Xfinity network, RTL8852BE (rtw89) capped at ~20 Mbps on kernel 7.0.0

[Alex Gavin <alex.gavin@candelatech.com>]

> On Aug 26, 2026, at 1:57 PM, Noah Yacob <noahgyacob@gmail.com> wrote:
> 
> Hello,
> 
> I'm reporting a throughput regression that appears to match an issue
> discussed on the Arch Linux forums
> (https://bbs.archlinux.org/viewtopic.php?id=313033), where other users
> ran into the same symptom.
> 
> - Wi-Fi throughput dropped from near-gigabit speeds to a hard ~20 Mbps cap.
> - Confirmed not an ISP or router issue: booting an older kernel
> (6.8.0-138-generic) on the same machine, same hardware, same network,
> restores normal (near-plan) speeds.
> - Confirmed not a driver-installation issue: the in-tree rtw89 driver
> is in use in both cases (no custom/out-of-tree driver).
> - The regression is reproducible simply by booting the newer kernel
> vs. the older one -- no other configuration changed.
> 
> Hardware / environment:
> - Wi-Fi chipset: Realtek RTL8852BE (rtw89, rtw8852be), PCIe
> - Driver in use: in-tree rtw89 (rtw89_8852be / rtw89_pci / rtw89_core
> / mac80211 / cfg80211)
> - Firmware: rtw8852b_fw-1.bin, version 0.29.29.5 (da87cccd), cmd version 0
> - OS: Linux Mint
> - Broken kernel: 7.0.0-30-generic
> - Working kernel: 6.8.0-138-generic (confirmed via dpkg -l | grep
> linux-image and booting via GRUB "Advanced options")
> - ISP: Comcast Xfinity, 1 Gbps plan
> 
> Symptom pattern:
> On the affected kernel, dmesg / journal shows mac80211 disabling HT
> ("required MCSes not supported, disabling HT"), and the link
> negotiates down to a 20 MHz, no-HT connection instead of HT/VHT/HE,
> which caps throughput at roughly 20 Mbps regardless of my ISP plan
> speed.
> 
> The fix that resolved this for other users in the linked Arch thread
> is a community patch that removes mac80211's basic MCS/NSS check
> (github.com/WoodyWoodster/mac80211-mcs-patch). That fix has since been
> picked up into Arch's own kernel package as of version 7.0.13.
> 
> I'm submitting this to add a confirmed data point (RTL8852BE, kernel
> 7.0.0, Xfinity) in case it's useful for tracking or prioritizing a fix
> upstream.
> 
> Happy to provide any other diagnostics that would help.

Per my understanding, this should be resolved by an April patch
which reduced the strictness of HT IE checks to accomodate this.
Link here [1].

I believe this landed in Linux v7.1 and was included in v6.18
and v7.0 releases from v6.18.36 [2] and v7.0.13 [3], respectively.

Best,

Alex

[1] https://lore.kernel.org/linux-wireless/99Mv9QEceyPrQhSP52MtAVmz0_kWJmzqotJjD9YW6LGLqk-AZloAueUyHCURilFkuqOh6Ecv8i2KKdSE1ujP3AnbU5QEouVisT1w_V3xdfc=@r26.me/
[2] https://lore.kernel.org/stable/2026061933-uproar-snarl-100e@gregkh/
[3] https://lore.kernel.org/stable/2026061959-baguette-handler-82ab@gregkh/