> mt76_npu_device_active() and mt76_ppe_device_active() read dev->mmio.npu
> and dev->mmio.ppe_dev. The mmio, usb and sdio bus structs share a union in
> struct mt76_dev, so on USB and SDIO these read unrelated data from the
> usb/sdio struct, which is non-NULL in practice.
> 
> mt76_npu_device_active() then returns true on USB, and
> mt76_rx_poll_complete() takes the offload path and skips
> mt76_rx_aggr_reorder(). RX A-MPDU subframes are delivered out of order and
> the peer's TCP stack treats that as loss: heavy retransmissions and reduced
> throughput in AP mode. Seen on mt7921u, mt7925u, mt76x2u and mt76x0u.
> 
> Gate both helpers on mt76_is_mmio() so they only run for the bus type that
> owns the mmio union member.
> 
> Fixes: 7fb554b1b623 ("wifi: mt76: Introduce the NPU generic layer")
> Cc: stable@vger.kernel.org
> Tested-by: Nick Morrow <morrownr@gmail.com>
> Signed-off-by: Devin Wittmayer <lucid_duck@justthetip.ca>

Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>

> ---
>  drivers/net/wireless/mediatek/mt76/mt76.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
> index 07955555f84d..a32ba7c23f92 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76.h
> +++ b/drivers/net/wireless/mediatek/mt76/mt76.h
> @@ -1736,12 +1736,12 @@ static inline int mt76_npu_send_txrx_addr(struct mt76_dev *dev, int ifindex,
>  
>  static inline bool mt76_npu_device_active(struct mt76_dev *dev)
>  {
> -	return !!rcu_access_pointer(dev->mmio.npu);
> +	return mt76_is_mmio(dev) && !!rcu_access_pointer(dev->mmio.npu);
>  }
>  
>  static inline bool mt76_ppe_device_active(struct mt76_dev *dev)
>  {
> -	return !!rcu_access_pointer(dev->mmio.ppe_dev);
> +	return mt76_is_mmio(dev) && !!rcu_access_pointer(dev->mmio.ppe_dev);
>  }
>  
>  static inline int mt76_npu_send_msg(struct airoha_npu *npu, int ifindex,
> -- 
> 2.55.0
>