linux-kernel - Re: [PATCH mt76 1/2] Revert "wifi: mt76: mt792x: improve monitor interface handling"

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Message-ID: <780b6778-ea0e-4fc9-8f35-83b5cd4940af@icloud.com>
Date: Thu, 20 Nov 2025 21:42:18 -0800
From: Alex Gavin <a_gavin@...oud.com>
To: Fedor Pchelkin <pchelkin@...ras.ru>, Felix Fietkau <nbd@....name>,
 Lorenzo Bianconi <lorenzo@...nel.org>,
 Ming Yen Hsieh <mingyen.hsieh@...iatek.com>
Cc: Ryder Lee <ryder.lee@...iatek.com>, Shayne Chen
 <shayne.chen@...iatek.com>, Sean Wang <sean.wang@...iatek.com>,
 linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mediatek@...ts.infradead.org, Matvey Kovalev
 <matvey.kovalev@...ras.ru>, lvc-project@...uxtesting.org
Subject: Re: [PATCH mt76 1/2] Revert "wifi: mt76: mt792x: improve monitor
 interface handling"

On 10/27/25 04:18, Fedor Pchelkin wrote:
> This reverts commit 55e95ce469d0c61041bae48b2ebb7fcbf6d1ba7f.
> 
> mt792x drivers don't seem to support multi-radio devices yet.  At least
> they don't mess with `struct wiphy_radio` at the moment.
> 
> Packet capturing on monitor interface doesn't work after the blamed patch:
> 
>   tcpdump -i wls6mon -n -vvv
> 
> Revert the NO_VIRTUAL_MONITOR feature for now to resolve the issue.
> 
> Found by Linux Verification Center (linuxtesting.org).
> 
> Fixes: 55e95ce469d0 ("wifi: mt76: mt792x: improve monitor interface handling")
> Signed-off-by: Fedor Pchelkin <pchelkin@...ras.ru>
> ---
> 
> Can't answer exactly *why* the capturing doesn't work after the patch:
> probably because the driver is just not prepared for NO_VIRTUAL_MONITOR.
> The feature isn't too obvious, especially that for some reason it was set
> in mt792x alongside WANT_MONITOR_VIF.  With a quick glance I might
> conclude that NO_VIRTUAL_MONITOR overrides WANT_MONITOR_VIF, they don't
> look compatible.
> 
>  drivers/net/wireless/mediatek/mt76/mt792x_core.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt792x_core.c b/drivers/net/wireless/mediatek/mt76/mt792x_core.c
> index 5b50bf94996e..f2ed16feb6c1 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt792x_core.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt792x_core.c
> @@ -688,7 +688,6 @@ int mt792x_init_wiphy(struct ieee80211_hw *hw)
>  	ieee80211_hw_set(hw, SUPPORTS_DYNAMIC_PS);
>  	ieee80211_hw_set(hw, SUPPORTS_VHT_EXT_NSS_BW);
>  	ieee80211_hw_set(hw, CONNECTION_MONITOR);
> -	ieee80211_hw_set(hw, NO_VIRTUAL_MONITOR);
>  	ieee80211_hw_set(hw, SUPPORTS_MULTI_BSSID);
>  	ieee80211_hw_set(hw, SUPPORTS_ONLY_HE_MULTI_BSSID);
>  

This patch fixed monitor vif-only packet capture for me when using both mt7921 and mt7921au chipset
radios. Without it I was only seeing broadcast and multicast traffic I believe. Tested using vanilla
6.18.0-rc6 as base.