Re: [net-next v4 08/12] net: bnxt: Implement software USO

On Fri, Mar 20, 2026 at 8:12 PM Joe Damato [off-list ref] 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.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Joe Damato <redacted>
---
 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     |   4 +
 drivers/net/ethernet/broadcom/bnxt/bnxt_gso.c | 206 ++++++++++++++++++
 2 files changed, 210 insertions(+)

Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>