Re: [PATCH wireless] wifi: b43: map the RX buffers DMA_BIDIRECTIONAL

[Michael Büsch]

Quite honestly, to me this looks like a lot of AI slop is sent to b43 these days.
Can you please slow down your submissions so that actual people get a chance to review the stuff?
Thanks!

-- 
Michael Büsch
https://bues.ch/


On Fri, 23 Oct 2026 12:06:53 -0700
Rosen Penev <rosenp@xxxxxxxxx> wrote:

> b43 poisons each RX buffer before it hands it to the device, and drops
> a buffer that still carries the poison, as the device sometimes skips
> one. The RX buffers are mapped and synced DMA_FROM_DEVICE. On a
> non-coherent CPU like the BCM4716 or the BCM4708, the map and the sync
> for the device then only invalidate the cache, so the poison written
> just before never reaches memory. A skipped buffer is read as whatever
> the memory held before, for a recycled buffer the data of its previous
> use: garbage frames, or a length that sends dma_rx() into its path for
> frames spanning several buffers.
> 
> Map, sync and unmap the RX buffers DMA_BIDIRECTIONAL, so that the
> poison is written back before the device gets the buffer.
> 
> Reported on a Netgear R6400 (BCM4708, BCM4331).
> 
> Fixes: cf68636a9773 ("b43: Refresh RX poison on buffer recycling")
> Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
> ---
>  drivers/net/wireless/broadcom/b43/dma.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/wireless/broadcom/b43/dma.c b/drivers/net/wireless/broadcom/b43/dma.c
> index 05da6987a845..c8585c6dff37 100644
> --- a/drivers/net/wireless/broadcom/b43/dma.c
> +++ b/drivers/net/wireless/broadcom/b43/dma.c
> @@ -353,8 +353,14 @@ static inline
>  		dmaaddr = dma_map_single(ring->dev->dev->dma_dev,
>  					 buf, len, DMA_TO_DEVICE);
>  	} else {
> +		/*
> +		 * Not DMA_FROM_DEVICE: on a non-coherent CPU, the map and
> +		 * the sync for the device would then only invalidate the
> +		 * cache, and the poison of b43_poison_rx_buffer() would
> +		 * never reach memory.
> +		 */
>  		dmaaddr = dma_map_single(ring->dev->dev->dma_dev,
> -					 buf, len, DMA_FROM_DEVICE);
> +					 buf, len, DMA_BIDIRECTIONAL);
>  	}
>  
>  	return dmaaddr;
> @@ -369,7 +375,7 @@ static inline
>  				 addr, len, DMA_TO_DEVICE);
>  	} else {
>  		dma_unmap_single(ring->dev->dev->dma_dev,
> -				 addr, len, DMA_FROM_DEVICE);
> +				 addr, len, DMA_BIDIRECTIONAL);
>  	}
>  }
>  
> @@ -379,7 +385,7 @@ static inline
>  {
>  	B43_WARN_ON(ring->tx);
>  	dma_sync_single_for_cpu(ring->dev->dev->dma_dev,
> -				    addr, len, DMA_FROM_DEVICE);
> +				    addr, len, DMA_BIDIRECTIONAL);
>  }
>  
>  static inline
> @@ -388,7 +394,7 @@ static inline
>  {
>  	B43_WARN_ON(ring->tx);
>  	dma_sync_single_for_device(ring->dev->dev->dma_dev,
> -				   addr, len, DMA_FROM_DEVICE);
> +				   addr, len, DMA_BIDIRECTIONAL);
>  }
>  
>  static inline

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