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

Subbaraya Sundeep
2026-03-13T11:38:11Z

Hi,

On 2026-03-13 at 14:50:59, Nicolai Buchwitz (nb@tipi-net.de) 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 <nb@tipi-net.de>
> ---
> .../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
>