ath12k_pull_mac_phy_cap_svc_ready_ext() derives the tx/rx chain-mask shift with find_first_bit((unsigned long *)&pdev_cap->rx_chain_mask, 32). pdev_cap->{tx,rx}_chain_mask are u32, but find_first_bit() treats the pointer as an array of unsigned long. On 64-bit big-endian, unsigned long is 8 bytes, so the u32 value ends up in the high 32 bits of the word while find_first_bit(..., 32) only scans the low 32 bits, i.e. the adjacent struct member. rx_chain_mask_shift is therefore computed as 32, ath12k_mac_setup_ht_vht_cap() evaluates cfg_rx_chainmask >> 32 == 0, and the driver advertises a VHT RX-MCS map with all streams "not supported". mac80211 then rejects the VHT capability ("Ignoring VHT IE ... due to invalid rx_mcs_map"), so the link only comes up as HT40 and never negotiates 80/160 MHz. tx_chain_mask_shift happens to scan a zero word and stays 0, so only the RX side is affected. Use __ffs() on the mask value instead of pointing find_first_bit() at the u32's storage. __ffs() takes its argument by value, so the shift is computed correctly regardless of word size or endianness. The chain masks are always non-zero here, so __ffs() is well defined. Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices") Cc: stable@vger.kernel.org Signed-off-by: Michael Pfeifroth --- drivers/net/wireless/ath/ath12k/wmi.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/drivers/net/wireless/ath/ath12k/wmi.c b/drivers/net/wireless/ath/ath12k/wmi.c --- a/drivers/net/wireless/ath/ath12k/wmi.c +++ b/drivers/net/wireless/ath/ath12k/wmi.c @@ -563,10 +563,8 @@ ath12k_pull_mac_phy_cap_svc_ready_ext(struct ath12k_wmi_pdev *wmi_handle, * for tx/rx chainmask which will be used to advertise supported ht/vht rates to * mac80211. */ - pdev_cap->tx_chain_mask_shift = - find_first_bit((unsigned long *)&pdev_cap->tx_chain_mask, 32); - pdev_cap->rx_chain_mask_shift = - find_first_bit((unsigned long *)&pdev_cap->rx_chain_mask, 32); + pdev_cap->tx_chain_mask_shift = __ffs(pdev_cap->tx_chain_mask); + pdev_cap->rx_chain_mask_shift = __ffs(pdev_cap->rx_chain_mask); if (supported_bands & WMI_HOST_WLAN_2GHZ_CAP) { cap_band = &pdev_cap->band[NL80211_BAND_2GHZ];