Subject: Re: [PATCH net-next 4/6] net: bcmgenet: add XDP_TX support

From: Subbaraya Sundeep <[email-masked]>
Date: Fri, 13 Mar 2026 17:07:37 +0530

Hi,

On 2026-03-13 at 14:50:59, Nicolai Buchwitz ([email-masked]) wrote:
> Implement XDP_TX by submitting XDP frames through the default TX ring
> (DESC_INDEX). The frame is DMA-mapped and placed into a single TX
> descriptor with SOP|EOP|APPEND_CRC flags.
> 
> The xdp_frame pointer is stored in the TX control block so that
> bcmgenet_free_tx_cb() can call xdp_return_frame() on TX completion,
> returning the page to the originating page_pool.
> 
> The page_pool DMA direction is changed from DMA_FROM_DEVICE to
> DMA_BIDIRECTIONAL to support the TX DMA mapping of received pages.
> 
> Signed-off-by: Nicolai Buchwitz <[email-masked]>
> ---
>  .../net/ethernet/broadcom/genet/bcmgenet.c    | 73 ++++++++++++++++++-
>  .../net/ethernet/broadcom/genet/bcmgenet.h    |  1 +
>  2 files changed, 71 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> index d43729fc2b1b..373ba5878ca1 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> @@ -1893,6 +1893,12 @@ static struct sk_buff *bcmgenet_free_tx_cb(struct device *dev,
>  		if (cb == GENET_CB(skb)->last_cb)
>  			return skb;
>  
> +	} else if (cb->xdpf) {
> +		dma_unmap_single(dev, dma_unmap_addr(cb, dma_addr),
> +				 dma_unmap_len(cb, dma_len), DMA_TO_DEVICE);
> +		dma_unmap_addr_set(cb, dma_addr, 0);
> +		xdp_return_frame(cb->xdpf);
> +		cb->xdpf = NULL;
>  	} else if (dma_unmap_addr(cb, dma_addr)) {
>  		dma_unmap_page(dev,
>  			       dma_unmap_addr(cb, dma_addr),
> @@ -2299,10 +2305,62 @@ static struct sk_buff *bcmgenet_xdp_build_skb(struct bcmgenet_rx_ring *ring,
>  	return skb;
>  }
>  
> +static bool bcmgenet_xdp_xmit_frame(struct bcmgenet_priv *priv,
> +				     struct xdp_frame *xdpf)
> +{
> +	struct bcmgenet_tx_ring *ring = &priv->tx_rings[DESC_INDEX];
> +	struct device *kdev = &priv->pdev->dev;
> +	struct enet_cb *tx_cb_ptr;
> +	dma_addr_t mapping;
> +	u32 len_stat;
> +
> +	spin_lock(&ring->lock);
> +
> +	if (ring->free_bds < 1) {
> +		spin_unlock(&ring->lock);
> +		return false;
> +	}
> +
> +	tx_cb_ptr = bcmgenet_get_txcb(priv, ring);
> +
> +	mapping = dma_map_single(kdev, xdpf->data, xdpf->len, DMA_TO_DEVICE);

AFAIU you are transmitting the frame received on a RQ which is from the page pool
and already dma mapped. Do you have to do dma_map again?

Thanks,
Sundeep

> +	if (dma_mapping_error(kdev, mapping)) {
> +		tx_cb_ptr->skb = NULL;
> +		tx_cb_ptr->xdpf = NULL;
> +		bcmgenet_put_txcb(priv, ring);
> +		spin_unlock(&ring->lock);
> +		return false;
> +	}
> +
> +	dma_unmap_addr_set(tx_cb_ptr, dma_addr, mapping);
> +	dma_unmap_len_set(tx_cb_ptr, dma_len, xdpf->len);
> +	tx_cb_ptr->skb = NULL;
> +	tx_cb_ptr->xdpf = xdpf;
> +
> +	len_stat = (xdpf->len << DMA_BUFLENGTH_SHIFT) |
> +		   (priv->hw_params->qtag_mask << DMA_TX_QTAG_SHIFT) |
> +		   DMA_TX_APPEND_CRC | DMA_SOP | DMA_EOP;
> +
> +	dmadesc_set(priv, tx_cb_ptr->bd_addr, mapping, len_stat);
> +
> +	ring->free_bds--;
> +	ring->prod_index++;
> +	ring->prod_index &= DMA_P_INDEX_MASK;
> +
> +	bcmgenet_tdma_ring_writel(priv, ring->index, ring->prod_index,
> +				  TDMA_PROD_INDEX);
> +
> +	spin_unlock(&ring->lock);
> +
> +	return true;
> +}
> +
>  static unsigned int
>  bcmgenet_run_xdp(struct bcmgenet_rx_ring *ring, struct bpf_prog *prog,
>  		 struct xdp_buff *xdp, struct page *rx_page)
>  {
> +	struct bcmgenet_priv *priv = ring->priv;
> +	struct xdp_frame *xdpf;
>  	unsigned int act;
>  
>  	act = bpf_prog_run_xdp(prog, xdp);
> @@ -2310,14 +2368,23 @@ bcmgenet_run_xdp(struct bcmgenet_rx_ring *ring, struct bpf_prog *prog,
>  	switch (act) {
>  	case XDP_PASS:
>  		return XDP_PASS;
> +	case XDP_TX:
> +		xdpf = xdp_convert_buff_to_frame(xdp);
> +		if (unlikely(!xdpf) ||
> +		    unlikely(!bcmgenet_xdp_xmit_frame(priv, xdpf))) {
> +			page_pool_put_full_page(ring->page_pool, rx_page,
> +						true);
> +			return XDP_DROP;
> +		}
> +		return XDP_TX;
>  	case XDP_DROP:
>  		page_pool_put_full_page(ring->page_pool, rx_page, true);
>  		return XDP_DROP;
>  	default:
> -		bpf_warn_invalid_xdp_action(ring->priv->dev, prog, act);
> +		bpf_warn_invalid_xdp_action(priv->dev, prog, act);
>  		fallthrough;
>  	case XDP_ABORTED:
> -		trace_xdp_exception(ring->priv->dev, prog, act);
> +		trace_xdp_exception(priv->dev, prog, act);
>  		page_pool_put_full_page(ring->page_pool, rx_page, true);
>  		return XDP_ABORTED;
>  	}
> @@ -2846,7 +2913,7 @@ static int bcmgenet_rx_ring_create_pool(struct bcmgenet_priv *priv,
>  		.pool_size = ring->size,
>  		.nid = NUMA_NO_NODE,
>  		.dev = &priv->pdev->dev,
> -		.dma_dir = DMA_FROM_DEVICE,
> +		.dma_dir = DMA_BIDIRECTIONAL,
>  		.offset = GENET_XDP_HEADROOM,
>  		.max_len = RX_BUF_LENGTH,
>  	};
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.h b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
> index 1459473ac1b0..192db0defbfc 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.h
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.h
> @@ -472,6 +472,7 @@ struct bcmgenet_rx_stats64 {
>  
>  struct enet_cb {
>  	struct sk_buff      *skb;
> +	struct xdp_frame    *xdpf;
>  	struct page         *rx_page;
>  	unsigned int        rx_page_offset;
>  	void __iomem *bd_addr;
> -- 
> 2.51.0
>