[PATCH] Skip ieee80211_verify_sta_ht_mcs_support check in non-strict mode

[PATCH] Skip ieee80211_verify_sta_ht_mcs_support check in non-strict mode

[Rio Liu]

Empty Message

[PATCH] Skip ieee80211_verify_sta_ht_mcs_support check in non-strict mode

[Rio Liu]

Some AP advertise 3 or 4 spatial stream MCS indexes in their basic
HT-MCS set. On cards with lower (2x2) spatial streams, the check would
fail, and we'd be stuck with no HT when it in fact work fine with
2-stream rate. This change makes it so the check is only performed in
strict mode.

Signed-off-by: Rio Liu <rio@r26.me>
---
My previous mail is showing up as empty on LKML for some reason.
Apologies for that, trying again.

There has been some reports that WIFI speed is capped on some routers:

Link: https://linuxcommunity.io/t/intel-ax210-speeds-capped-at-20-mbps-on-multiple-distros/6708/28
Link: https://bbs.archlinux.org/viewtopic.php?id=312952
Link: https://bbs.archlinux.org/viewtopic.php?id=313033
Link: https://www.reddit.com/r/Rogers/comments/1s89j9f/xb8_5ghz_dfs_channel_broadcasting_at_54_mbps/
Link: https://www.reddit.com/r/Comcast_Xfinity/comments/1s7fc3f/recent_firmware_update_to_wifi_gateway_breaking/
Link: https://www.reddit.com/r/Comcast_Xfinity/comments/1sg9r6z/slow_internet_for_linux_computers/

Apparently some APs advertises higher MIMO streams than the device
supports. In that case, HT-MCS check would fail and we fall back to
20MHz channel. A patch exists here that bypasses the check completely:
https://github.com/WoodyWoodster/mac80211-mcs-patch, and have been
reported to get 80MHz channel back.

This patch adds a check on STRICT flag before verifying HT MCS set from
the AP, similar to how it is done in ieee80211_verify_sta_vht_mcs_support.
---
 net/mac80211/mlme.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 810bea1aacc5..0e33733ac634 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -419,6 +419,15 @@ ieee80211_verify_sta_ht_mcs_support(struct ieee80211_sub_if_data *sdata,
 	memcpy(&sta_ht_cap, &sband->ht_cap, sizeof(sta_ht_cap));
 	ieee80211_apply_htcap_overrides(sdata, &sta_ht_cap);

+	/*
+	 * Some AP advertise 3 or 4 spatial stream MCS indexes in their basic HT-MCS
+	 * set. On cards with lower (2x2) spatial streams, the check would fail, and
+	 * we'd be stuck with no HT when it in fact work fine with 2-stream rate. So
+	 * check it only in strict mode.
+	 */
+	if (!ieee80211_hw_check(&sdata->local->hw, STRICT))
+		return true;
+
 	/*
 	 * P802.11REVme/D7.0 - 6.5.4.2.4
 	 * ...
--
base-commit: d65b175cfac64ee65506eea7fa573d291a9694ca

Re: [PATCH] Skip ieee80211_verify_sta_ht_mcs_support check in non-strict mode

[Johannes Berg]

On Tue, 2026-04-14 at 05:02 +0000, Rio Liu wrote:
> Some AP advertise 3 or 4 spatial stream MCS indexes in their basic
> HT-MCS set. On cards with lower (2x2) spatial streams, the check would
> fail, and we'd be stuck with no HT when it in fact work fine with
> 2-stream rate. This change makes it so the check is only performed in
> strict mode.
> 
> Signed-off-by: Rio Liu <rio@r26.me>
> ---

Should probably have a Fixes tag for this?

> Link: https://linuxcommunity.io/t/intel-ax210-speeds-capped-at-20-mbps-on-multiple-distros/6708/28
> Link: https://bbs.archlinux.org/viewtopic.php?id=312952
> Link: https://bbs.archlinux.org/viewtopic.php?id=313033
> Link: https://www.reddit.com/r/Rogers/comments/1s89j9f/xb8_5ghz_dfs_channel_broadcasting_at_54_mbps/
> Link: https://www.reddit.com/r/Comcast_Xfinity/comments/1s7fc3f/recent_firmware_update_to_wifi_gateway_breaking/
> Link: https://www.reddit.com/r/Comcast_Xfinity/comments/1sg9r6z/slow_internet_for_linux_computers/

> +	/*
> +	 * Some AP advertise 3 or 4 spatial stream MCS indexes in their basic HT-MCS
> +	 * set. On cards with lower (2x2) spatial streams, the check would fail, and
> +	 * we'd be stuck with no HT when it in fact work fine with 2-stream rate. So
> +	 * check it only in strict mode.
> +	 */
> +	if (!ieee80211_hw_check(&sdata->local->hw, STRICT))
> +		return true;

And generally we prefer to have some indication in the comment which APs
were affected (though I see the VHT one also didn't have that), such as
in ieee80211_verify_peer_he_mcs_support().

johannes