[PATCH net-next v8 0/7] net: bcmgenet: add XDP support

Nicolai Buchwitz
2026-04-28T20:59:38Z

Add XDP support to the bcmgenet driver, covering XDP_PASS, XDP_DROP,
XDP_TX, XDP_REDIRECT, and ndo_xdp_xmit.

The first patch converts the RX path from the existing kmalloc-based
allocation to page_pool, which is a prerequisite for XDP. The remaining
patches incrementally add XDP functionality and per-action statistics.

Tested on Raspberry Pi CM4 (BCM2711, bcmgenet, 1Gbps link):
- XDP_PASS: 943 Mbit/s TX, 935 Mbit/s RX (no regression vs baseline)
- XDP_PASS latency: 0.164ms avg, 0% packet loss
- XDP_DROP: all inbound traffic blocked as expected
- XDP_TX: TX counter increments (packet reflection working)
- Link flap with XDP attached: no errors
- Program swap under iperf3 load: no errors
- Upstream XDP selftests (xdp.py): pass_sb, drop_sb, tx_sb passing
- XDP-based EtherCAT master (~37 kHz cycle rate, all packet processing
in BPF/XDP), stable over multiple days

Previous versions:
v7: https://lore.kernel.org/netdev/20260416054743.1289191-1-nb@tipi-net.de/
v6: https://lore.kernel.org/netdev/20260406083536.839517-1-nb@tipi-net.de/
v5: https://lore.kernel.org/netdev/20260328230513.415790-1-nb@tipi-net.de/
v4: https://lore.kernel.org/netdev/20260323120539.136029-1-nb@tipi-net.de/
v3: https://lore.kernel.org/netdev/20260319115402.353509-1-nb@tipi-net.de/
v2: https://lore.kernel.org/netdev/20260315214914.1555777-1-nb@tipi-net.de/
v1: https://lore.kernel.org/netdev/20260313092101.1344954-1-nb@tipi-net.de/

Changes since v7:
- No code changes; resubmitted after net-next reopened.

Changes since v6:
- Removed GENET_XDP_HEADROOM alias, use XDP_PACKET_HEADROOM
directly. (Jakub Kicinski)
- Dropped redundant __GFP_NOWARN from page_pool_alloc_pages(),
page_pool adds it automatically. (Jakub Kicinski)
- Removed floating code block in desc_rx, moved variables to outer
scope. (Jakub Kicinski)
- Make bcmgenet_run_xdp() return XDP_PASS when no program is set,
removing the if (xdp_prog) indentation from desc_rx.
(Jakub Kicinski)

Changes since v5:
- Refactored desc_rx: always prepare xdp_buff and use
bcmgenet_xdp_build_skb for both XDP and non-XDP paths, treating
no-prog as XDP_PASS. (Jakub Kicinski)
- Removed synchronize_net() before bpf_prog_put(), RCU handles
the grace period. (Jakub Kicinski)
- Save status->rx_csum before running XDP program to prevent
bpf_xdp_adjust_head from corrupting the RSB checksum.
(Jakub Kicinski)
- Tightened TSB headroom check to include sizeof(struct xdp_frame).
(Jakub Kicinski)
- Fixed reclaim gating: check for pending frames on the XDP TX ring
instead of priv->xdp_prog, so in-flight frames are still reclaimed
after XDP program detach. (Jakub Kicinski)
- Removed dead len -= ETH_FCS_LEN in patch 1. (Mohsin Bashir)
- Added patch 7: minimal ndo_change_mtu that rejects MTU values
incompatible with XDP when a program is attached. (Mohsin Bashir,
Florian Fainelli)

Changes since v4:
- Fixed unused variable warning: moved tx_ring declaration from
patch 4 to patch 5 where it is first used. (Jakub Kicinski)

Changes since v3:
- Fixed xdp_prepare_buff() called with meta_valid=false, causing
bcmgenet_xdp_build_skb() to compute metasize=UINT_MAX and corrupt
skb meta_len. Now passes true. (Simon Horman)
- Removed bcmgenet_dump_tx_queue() for ring 16 in bcmgenet_timeout().
Ring 16 has no netdev TX queue, so netdev_get_tx_queue(dev, 16)
accessed beyond the allocated _tx array. (Simon Horman)
- Fixed checkpatch alignment warnings in patches 4 and 5.

Changes since v2:
- Fixed page leak on partial bcmgenet_alloc_rx_buffers() failure:
free already-allocated rx_cbs before destroying page pool.
(Simon Horman)
- Fixed GENET_Q16_TX_BD_CNT defined as 64 instead of 32.
(Simon Horman)
- Moved XDP TX ring to a separate struct member (xdp_tx_ring)
instead of expanding tx_rings[] to DESC_INDEX+1. (Justin Chen)
- Added synchronize_net() before bpf_prog_put() in XDP prog swap.
- Removed goto drop_page inside switch; inlined page_pool_put
calls in each failure path. (Justin Chen)
- Removed unnecessary curly braces around case XDP_TX. (Justin Chen)
- Moved int err hoisting from patch 2 to patch 1. (Justin Chen)
- Kept return type on same line as function name, per driver
convention. (Justin Chen)
- XDP TX packets/bytes now counted in TX reclaim for standard
network statistics.

Changes since v1:
- Fixed tx_rings[DESC_INDEX] out-of-bounds access. Expanded array
to DESC_INDEX+1 and initialized ring 16 with dedicated BDs.
- Use ring 16 (hardware default descriptor ring) for XDP TX,
isolating from normal SKB TX queues.
- Piggyback ring 16 TX completion on RX NAPI poll (INTRL2_1 bit
collision with RX ring 0).
- Fixed ring 16 TX reclaim: skip INTRL2_1 clear, skip BQL
completion, use non-destructive reclaim in RX poll path.
- Prepend zeroed TSB before XDP TX frame data (TBUF_64B_EN requires
64-byte struct status_64 prefix on all TX buffers).
- Tested with upstream XDP selftests (xdp.py): pass_sb, drop_sb,
tx_sb all passing. The multi-buffer tests (pass_mb, drop_mb,
tx_mb) fail because bcmgenet does not support jumbo frames /
MTU changes; I plan to add ndo_change_mtu support in a follow-up
series.

Nicolai Buchwitz (7):
net: bcmgenet: convert RX path to page_pool
net: bcmgenet: register xdp_rxq_info for each RX ring
net: bcmgenet: add basic XDP support (PASS/DROP)
net: bcmgenet: add XDP_TX support
net: bcmgenet: add XDP_REDIRECT and ndo_xdp_xmit support
net: bcmgenet: add XDP statistics counters
net: bcmgenet: reject MTU changes incompatible with XDP

drivers/net/ethernet/broadcom/Kconfig | 1 +
.../net/ethernet/broadcom/genet/bcmgenet.c | 637 +++++++++++++++---
.../net/ethernet/broadcom/genet/bcmgenet.h | 19 +
3 files changed, 559 insertions(+), 98 deletions(-)

--
2.51.0