Re: [net-next v7 07/10] net: bnxt: Implement software USO

[Eric Dumazet]

On Wed, Apr 1, 2026 at 4:38 PM Joe Damato <joe@xxxxxxx> wrote:
>
> Implement bnxt_sw_udp_gso_xmit() using the core tso_dma_map API and
> the pre-allocated TX inline buffer for per-segment headers.
>
> The xmit path:
> 1. Calls tso_start() to initialize TSO state
> 2. Stack-allocates a tso_dma_map and calls tso_dma_map_init() to
>    DMA-map the linear payload and all frags upfront.
> 3. For each segment:
>    - Copies and patches headers via tso_build_hdr() into the
>      pre-allocated tx_inline_buf (DMA-synced per segment)
>    - Counts payload BDs via tso_dma_map_count()
>    - Emits long BD (header) + ext BD + payload BDs
>    - Payload BDs use tso_dma_map_next() which yields (dma_addr,
>      chunk_len, mapping_len) tuples.
>
> Header BDs set dma_unmap_len=0 since the inline buffer is pre-allocated
> and unmapped only at ring teardown.
>
> Completion state is updated by calling tso_dma_map_completion_save() for
> the last segment.
>
> Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
> Signed-off-by: Joe Damato <joe@xxxxxxx>
> ---
>  v7:
>    - Dropped Pavan's Reviewed-by as some changes were made.
>    - Updated struct bnxt_sw_tx_bd to embed a tso_dma_map_completion_state
>      struct for tracking completion state.
>    - Dropped an unnecessary slot check.
>    - Eliminated an ugly looking ternary to simplify the code.
>    - Call tso_dma_map_completion_save to update completion state.
>
>  v6:
>    - Addressed Paolo's feedback where the IOVA API could fail transiently,
>      leaving stale state in iova_state. Fix this by always copying the state,
>      noting that dma_iova_try_alloc is called unconditionally in the
>      tso_dma_map_init function (via tso_dma_iova_try), which zeroes the state
>      even if the API can't be used.
>    - Since this was a very minor change, I retained Pavan's Reviewed-by.
>
>  v5:
>    - Added __maybe_unused to last_unmap_len and last_unmap_addr to silence a
>      build warning when CONFIG_NEED_DMA_MAP_STATE is disabled. No functional
>      changes.
>    - Added Pavan's Reviewed-by.
>
>  v4:
>    - Fixed the early return issue Pavan pointed out when num_segs <= 1; use the
>      drop label instead of returning.
>
>  v3:
>    - Added iova_state and iova_total_len to struct bnxt_sw_tx_bd.
>    - Stores iova_state on the last segment's tx_buf during xmit.
>
>  rfcv2:
>    - set the unmap len on the last descriptor, so that when completions fire
>      only the last completion unmaps the region.
>
>  drivers/net/ethernet/broadcom/bnxt/bnxt.h     |   3 +
>  drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c | 197 ++++++++++++++++++
>  2 files changed, 200 insertions(+)
>
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.h b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> index b5b84d1e5217..993b215413c7 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.h
> @@ -11,6 +11,8 @@
>  #ifndef BNXT_H
>  #define BNXT_H
>
> +#include <net/tso.h>
> +
>  #define DRV_MODULE_NAME                "bnxt_en"
>
>  /* DO NOT CHANGE DRV_VER_* defines
> @@ -899,6 +901,7 @@ struct bnxt_sw_tx_bd {
>                 u16                     rx_prod;
>                 u16                     txts_prod;
>         };
> +       struct tso_dma_map_completion_state sw_gso_cstate;
>  };
>
>  #define BNXT_SW_GSO_MID                1
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c
> index b296769ee4fe..b0f8126b6903 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c
> @@ -19,11 +19,208 @@
>  #include "bnxt.h"
>  #include "bnxt_gso.h"
>
> +static u32 bnxt_sw_gso_lhint(unsigned int len)
> +{
> +       if (len <= 512)
> +               return TX_BD_FLAGS_LHINT_512_AND_SMALLER;
> +       else if (len <= 1023)
> +               return TX_BD_FLAGS_LHINT_512_TO_1023;
> +       else if (len <= 2047)
> +               return TX_BD_FLAGS_LHINT_1024_TO_2047;
> +       else
> +               return TX_BD_FLAGS_LHINT_2048_AND_LARGER;
> +}
> +
>  netdev_tx_t bnxt_sw_udp_gso_xmit(struct bnxt *bp,
>                                  struct bnxt_tx_ring_info *txr,
>                                  struct netdev_queue *txq,
>                                  struct sk_buff *skb)
>  {
> +       unsigned int last_unmap_len __maybe_unused = 0;
> +       dma_addr_t last_unmap_addr __maybe_unused = 0;
> +       struct bnxt_sw_tx_bd *last_unmap_buf = NULL;
> +       unsigned int hdr_len, mss, num_segs;
> +       struct pci_dev *pdev = bp->pdev;
> +       unsigned int total_payload;
> +       struct tso_dma_map map;
> +       u32 vlan_tag_flags = 0;
> +       int i, bds_needed;
> +       struct tso_t tso;
> +       u16 cfa_action;
> +       u16 prod;
> +
> +       hdr_len = tso_start(skb, &tso);
> +       mss = skb_shinfo(skb)->gso_size;
> +       total_payload = skb->len - hdr_len;
> +       num_segs = DIV_ROUND_UP(total_payload, mss);
> +
> +       /* Zero the csum fields so tso_build_hdr will propagate zeroes into
> +        * every segment header. HW csum offload will recompute from scratch.
> +        */

We might need a call to skb_cow_head(skb, 0) before changing ->check
(or anything in skb->head)

Alternative would be to perform the clears after each tso_build_hdr()
and leave skb->head untouched.


> +       udp_hdr(skb)->check = 0;
> +       if (!tso.ipv6)
> +               ip_hdr(skb)->check = 0;
> +
> +       if (unlikely(num_segs <= 1))
> +               goto drop;
> +
> +       /* Upper bound on the number of descriptors needed.
> +        *
> +        * Each segment uses 1 long BD + 1 ext BD + payload BDs, which is
> +        * at most num_segs + nr_frags (each frag boundary crossing adds at
> +        * most 1 extra BD).
> +        */
> +       bds_needed = 3 * num_segs + skb_shinfo(skb)->nr_frags + 1;
> +
> +       if (unlikely(bnxt_tx_avail(bp, txr) < bds_needed)) {
> +               netif_txq_try_stop(txq, bnxt_tx_avail(bp, txr),
> +                                  bp->tx_wake_thresh);
> +               return NETDEV_TX_BUSY;
> +       }
> +
> +       if (unlikely(tso_dma_map_init(&map, &pdev->dev, skb, hdr_len)))
> +               goto drop;
> +
> +       cfa_action = bnxt_xmit_get_cfa_action(skb);
> +       if (skb_vlan_tag_present(skb)) {
> +               vlan_tag_flags = TX_BD_CFA_META_KEY_VLAN |
> +                                skb_vlan_tag_get(skb);
> +               if (skb->vlan_proto == htons(ETH_P_8021Q))
> +                       vlan_tag_flags |= 1 << TX_BD_CFA_META_TPID_SHIFT;
> +       }
> +
> +       prod = txr->tx_prod;
> +
> +       for (i = 0; i < num_segs; i++) {
> +               unsigned int seg_payload = min_t(unsigned int, mss,
> +                                                total_payload - i * mss);
> +               u16 slot = (txr->tx_inline_prod + i) &
> +                          (BNXT_SW_USO_MAX_SEGS - 1);
> +               struct bnxt_sw_tx_bd *tx_buf;
> +               unsigned int mapping_len;
> +               dma_addr_t this_hdr_dma;
> +               unsigned int chunk_len;
> +               unsigned int offset;
> +               dma_addr_t dma_addr;
> +               struct tx_bd *txbd;
> +               void *this_hdr;
> +               int bd_count;
> +               __le32 csum;
> +               bool last;
> +               u32 flags;
> +
> +               last = (i == num_segs - 1);
> +               offset = slot * TSO_HEADER_SIZE;
> +               this_hdr = txr->tx_inline_buf + offset;
> +               this_hdr_dma = txr->tx_inline_dma + offset;
> +
> +               tso_build_hdr(skb, this_hdr, &tso, seg_payload, last);
> +
> +               dma_sync_single_for_device(&pdev->dev, this_hdr_dma,
> +                                          hdr_len, DMA_TO_DEVICE);
> +
> +               bd_count = tso_dma_map_count(&map, seg_payload);
> +
> +               tx_buf = &txr->tx_buf_ring[RING_TX(bp, prod)];
> +               txbd = &txr->tx_desc_ring[TX_RING(bp, prod)][TX_IDX(prod)];
> +
> +               tx_buf->skb = skb;
> +               tx_buf->nr_frags = bd_count;
> +               tx_buf->is_push = 0;
> +               tx_buf->is_ts_pkt = 0;
> +
> +               dma_unmap_addr_set(tx_buf, mapping, this_hdr_dma);
> +               dma_unmap_len_set(tx_buf, len, 0);
> +
> +               if (last) {
> +                       tx_buf->is_sw_gso = BNXT_SW_GSO_LAST;
> +                       tso_dma_map_completion_save(&map, &tx_buf->sw_gso_cstate);
> +               } else {
> +                       tx_buf->is_sw_gso = BNXT_SW_GSO_MID;
> +               }
> +
> +               flags = (hdr_len << TX_BD_LEN_SHIFT) |
> +                       TX_BD_TYPE_LONG_TX_BD |
> +                       TX_BD_CNT(2 + bd_count);
> +
> +               flags |= bnxt_sw_gso_lhint(hdr_len + seg_payload);
> +
> +               txbd->tx_bd_len_flags_type = cpu_to_le32(flags);
> +               txbd->tx_bd_haddr = cpu_to_le64(this_hdr_dma);
> +               txbd->tx_bd_opaque = SET_TX_OPAQUE(bp, txr, prod,
> +                                                  2 + bd_count);
> +
> +               csum = cpu_to_le32(TX_BD_FLAGS_TCP_UDP_CHKSUM |
> +                                  TX_BD_FLAGS_IP_CKSUM);
> +
> +               prod = NEXT_TX(prod);
> +               bnxt_init_ext_bd(bp, txr, prod, csum,
> +                                vlan_tag_flags, cfa_action);
> +
> +               /* set dma_unmap_len on the LAST BD touching each
> +                * region. Since completions are in-order, the last segment
> +                * completes after all earlier ones, so the unmap is safe.
> +                */
> +               while (tso_dma_map_next(&map, &dma_addr, &chunk_len,
> +                                       &mapping_len, seg_payload)) {
> +                       prod = NEXT_TX(prod);
> +                       txbd = &txr->tx_desc_ring[TX_RING(bp, prod)][TX_IDX(prod)];
> +                       tx_buf = &txr->tx_buf_ring[RING_TX(bp, prod)];
> +
> +                       txbd->tx_bd_haddr = cpu_to_le64(dma_addr);
> +                       dma_unmap_addr_set(tx_buf, mapping, dma_addr);
> +                       dma_unmap_len_set(tx_buf, len, 0);
> +                       tx_buf->skb = NULL;
> +                       tx_buf->is_sw_gso = 0;
> +
> +                       if (mapping_len) {
> +                               if (last_unmap_buf) {
> +                                       dma_unmap_addr_set(last_unmap_buf,
> +                                                          mapping,
> +                                                          last_unmap_addr);
> +                                       dma_unmap_len_set(last_unmap_buf,
> +                                                         len,
> +                                                         last_unmap_len);
> +                               }
> +                               last_unmap_addr = dma_addr;
> +                               last_unmap_len = mapping_len;
> +                       }
> +                       last_unmap_buf = tx_buf;
> +
> +                       flags = chunk_len << TX_BD_LEN_SHIFT;
> +                       txbd->tx_bd_len_flags_type = cpu_to_le32(flags);
> +                       txbd->tx_bd_opaque = 0;
> +
> +                       seg_payload -= chunk_len;
> +               }
> +
> +               txbd->tx_bd_len_flags_type |=
> +                       cpu_to_le32(TX_BD_FLAGS_PACKET_END);
> +
> +               prod = NEXT_TX(prod);
> +       }
> +
> +       if (last_unmap_buf) {
> +               dma_unmap_addr_set(last_unmap_buf, mapping, last_unmap_addr);
> +               dma_unmap_len_set(last_unmap_buf, len, last_unmap_len);
> +       }
> +
> +       txr->tx_inline_prod += num_segs;
> +
> +       netdev_tx_sent_queue(txq, skb->len);
> +
> +       WRITE_ONCE(txr->tx_prod, prod);
> +       /* Sync BDs before doorbell */
> +       wmb();
> +       bnxt_db_write(bp, &txr->tx_db, prod);
> +
> +       if (unlikely(bnxt_tx_avail(bp, txr) <= bp->tx_wake_thresh))
> +               netif_txq_try_stop(txq, bnxt_tx_avail(bp, txr),
> +                                  bp->tx_wake_thresh);
> +
> +       return NETDEV_TX_OK;
> +
> +drop:
>         dev_kfree_skb_any(skb);
>         dev_core_stats_tx_dropped_inc(bp->dev);
>         return NETDEV_TX_OK;
> --
> 2.52.0
>