[PATCH v2] wifi: ath12k: fix incorrect HT/VHT/HE/EHT MCS reporting in monitor mode

[Tamizh Raja]

On Tue, May 5, 2026 at 9:40 AM kwan1996 <laicheehou9 at gmail.com> wrote:
>
> In monitor mode, the driver incorrectly assigns the legacy rate
> to the rate_idx field of the radiotap header for HT/VHT/HE/EHT
> frames, ignoring the actual MCS value parsed from the hardware.
>
> This causes packet analyzers (like Wireshark) to display incorrect
> MCS values (e.g., legacy base rates instead of the true MCS).
>
> Fix this by assigning ppdu_info->mcs instead of ppdu_info->rate
> for HT/VHT/HE/EHT frame types in ath12k_dp_mon_fill_rx_rate()
> and ath12k_dp_mon_update_radiotap().
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=220864
>
> Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-QCAHKSWPL_SILICONZ
>
> Signed-off-by: kwan1996 <laicheehou9 at gmail.com>
>
> ---
>
> v2: Fix indentation and formatting issues in v1.
>
> ---
>  drivers/net/wireless/ath/ath12k/dp_mon.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath12k/dp_mon.c b/drivers/net/wireless/ath/ath12k/dp_mon.c
> index 39d1967..4119bb8 100644
> --- a/drivers/net/wireless/ath/ath12k/dp_mon.c
> +++ b/drivers/net/wireless/ath/ath12k/dp_mon.c
> @@ -1925,6 +1925,7 @@ ath12k_dp_mon_fill_rx_rate(struct ath12k *ar,
>                 }
>                 break;
>         case RX_MSDU_START_PKT_TYPE_11N:
> +               rate_mcs = ppdu_info->mcs;

Can we assign this rate_mcs before the switch case? Since in all cases
we are assigning unmodified ppdu_info->mcs.
>                 rx_status->encoding = RX_ENC_HT;
>                 if (rate_mcs > ATH12K_HT_MCS_MAX) {
>                         ath12k_warn(ar->ab,
> @@ -1937,6 +1938,7 @@ ath12k_dp_mon_fill_rx_rate(struct ath12k *ar,
>                         rx_status->enc_flags |= RX_ENC_FLAG_SHORT_GI;
>                 break;
>         case RX_MSDU_START_PKT_TYPE_11AC:
> +               rate_mcs = ppdu_info->mcs;
>                 rx_status->encoding = RX_ENC_VHT;
>                 rx_status->rate_idx = rate_mcs;
>                 if (rate_mcs > ATH12K_VHT_MCS_MAX) {
> @@ -1949,6 +1951,7 @@ ath12k_dp_mon_fill_rx_rate(struct ath12k *ar,
>                         rx_status->enc_flags |= RX_ENC_FLAG_SHORT_GI;
>                 break;
>         case RX_MSDU_START_PKT_TYPE_11AX:
> +               rate_mcs = ppdu_info->mcs;
>                 rx_status->rate_idx = rate_mcs;
>                 if (rate_mcs > ATH12K_HE_MCS_MAX) {
>                         ath12k_warn(ar->ab,
> @@ -1960,6 +1963,7 @@ ath12k_dp_mon_fill_rx_rate(struct ath12k *ar,
>                 rx_status->he_gi = ath12k_he_gi_to_nl80211_he_gi(sgi);
>                 break;
>         case RX_MSDU_START_PKT_TYPE_11BE:
> +               rate_mcs = ppdu_info->mcs;
>                 rx_status->rate_idx = rate_mcs;
>                 if (rate_mcs > ATH12K_EHT_MCS_MAX) {
>                         ath12k_warn(ar->ab,
> @@ -2259,13 +2263,13 @@ static void ath12k_dp_mon_update_radiotap(struct ath12k *ar,
>                 rxs->encoding = RX_ENC_HE;
>                 ptr = skb_push(mon_skb, sizeof(struct ieee80211_radiotap_he));
>                 ath12k_dp_mon_rx_update_radiotap_he(ppduinfo, ptr);
> -               rxs->rate_idx = ppduinfo->rate;
> +               rxs->rate_idx = ppduinfo->mcs;
>         } else if (ppduinfo->vht_flags) {
>                 rxs->encoding = RX_ENC_VHT;
> -               rxs->rate_idx = ppduinfo->rate;
> +               rxs->rate_idx = ppduinfo->mcs;
>         } else if (ppduinfo->ht_flags) {
>                 rxs->encoding = RX_ENC_HT;
> -               rxs->rate_idx = ppduinfo->rate;
> +               rxs->rate_idx = ppduinfo->mcs;

rate_idx should be assigned with ppdu_info->rate only not mcs.

>         } else {
>                 rxs->encoding = RX_ENC_LEGACY;
>                 sband = &ar->mac.sbands[rxs->band];
> --
> 2.34.1
>
>