Re: [PATCH ath-current] wifi: ath12k: fix EHT TX MCS limitation due to wrong 20 MHz-only parsing

[Rameshkumar Sundaram <rameshkumar.sundaram@oss.qualcomm.com>]

On 5/14/2026 9:02 AM, Baochen Qiang wrote:
> When connecting to an AP configured for EHT 20 MHz with a full EHT
> MCS/NSS map (supporting MCS 0-13)
> 
> Supported EHT-MCS and NSS Set
>      EHT-MCS Map (BW <= 80MHz): 0x444444
>          .... .... .... .... .... 0100 = Rx Max Nss That Supports EHT-MCS 0-9: 4
>          .... .... .... .... 0100 .... = Tx Max Nss That Supports EHT-MCS 0-9: 4
>          .... .... .... 0100 .... .... = Rx Max Nss That Supports EHT-MCS 10-11: 4
>          .... .... 0100 .... .... .... = Tx Max Nss That Supports EHT-MCS 10-11: 4
>          .... 0100 .... .... .... .... = Rx Max Nss That Supports EHT-MCS 12-13: 4
>          0100 .... .... .... .... .... = Tx Max Nss That Supports EHT-MCS 12-13: 4
> 
> TX throughput is observed to be significantly lower than expected.
> Investigation shows that TX rates are limited to EHT MCS 11, even though
> the AP advertises support for EHT MCS 12/13.
> 
> The root cause is an incorrect parsing of the Supported EHT-MCS and NSS
> Set element in ath12k_peer_assoc_h_eht().
> 
> IEEE Std 802.11be-2024 Figure 9-1074as describes the format for 20
> MHz-Only Non-AP STAs.
> 
> IEEE Std 802.11be-2024 Figure 9-1074at describes the format for all
> other AP and non-AP STAs.
> 
> Currently the first format is parsed when the peer advertises no wider
> HE channel width support, without considering whether it is an AP or a
> non-AP STA. This is incorrect: the peer AP's capabilities must be parsed
> using Figure 9-1074at even when it operates on 20 MHz only. Parsing it
> as Figure 9-1074as causes rx_tx_mcs13_max_nss to be interpreted as zero,
> which is then passed to firmware, leading firmware to assume the peer
> does not support MCS 13 and to limit TX rates at MCS 11.
> 
> Fix this by parsing the Figure 9-1074as format only when the peer is a
> 20 MHz-Only non-AP STA, i.e. when the local interface operates as AP or
> mesh point.
> 
> Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c5-00302-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.115823.3
> 
> Fixes: 6c95151e2e77 ("wifi: ath12k: Add EHT MCS/NSS rates to Peer Assoc")
> Signed-off-by: Baochen Qiang <baochen.qiang@oss.qualcomm.com>
Reviewed-by: Rameshkumar Sundaram <rameshkumar.sundaram@oss.qualcomm.com>