[RFC PATCH net-next 0/5] net: ethernet: zte: zx279128s: offload flows to and from WLAN interfaces

[Agustin Santiago Isasmendi <isasmendi.agus@gmail.com>]

Hi,

This series lets the ZX279128S switch driver offload flows whose ingress
or egress is a mac80211 AP interface, so that WiFi <-> WAN NAT traffic
no longer goes through the CPU's forwarding path.  It is based on Navid
Ghahremani's v2 platform series, which adds the SoC and the driver:

  https://lore.kernel.org/r/20261014072109.1759502-1-ghahramani.navid@gmail.com

The switch fabric has a second DMA engine (a ring pair the vendor
firmware uses for exactly this) and 16 "WLAN logical ports" that a
classifier entry can name as ingress or egress.  Patch 3 adds the ring
and the ports; patch 4 binds a mac80211 interface to a port on first
use and accepts flows from the flowtable in both directions; patch 5
adds debugfs testing aids.  Patches 1 and 2 describe the engine's
interrupt.  The WLAN drivers are not touched: the frames the fabric
forwards are handed to the interface's normal transmit path, and the
frames of offloaded flows are picked up on the interface's ingress hook
and injected into the ring.  Any mac80211 driver works.

This is not a WED-like path: the SoC has no block that chains the two
DMA engines, so the CPU still runs the WLAN driver's own transmit and
receive paths for these frames and moves the buffers between the rings
(no copies on the forwarded path).  What it no longer does is the
bridge, routing, conntrack and NAT work, which is where the CPU time
went: CPU0 drops from 54 % to 13-25 % at the rates below.  This is also
how the vendor firmware uses the engine.

Sent as RFC because:

- the base series is not merged yet, so this cannot be applied as is;
- a mac80211 AP interface cannot be put in an offload-enabled flowtable
  today, since mac80211 answers -EOPNOTSUPP to TC_SETUP_FT and
  nf_tables rejects the device.  This series was tested with Felix
  Fietkau's OpenWrt patch that ignores -EOPNOTSUPP there
  (target/linux/generic/pending-6.18/
  701-netfilter-nf_tables-ignore-EOPNOTSUPP-on-flowtable-d.patch).
  Felix, do you plan to send that upstream?  Without it, or something
  like it, this feature cannot be enabled on mainline;
- design: binding a WLAN interface to a switch port from the ethernet
  driver, through the interface's regular paths, keeps the WLAN drivers
  out of it.  I would like to know whether that is acceptable or
  whether this should go through something closer to the mediatek WED
  model.

The SoC has an unrelated problem under WiFi traffic: a PCIe read on one
CPU deadlocks against L2C-310 maintenance on the other, discussed in

  https://lore.kernel.org/r/20261110153522.1620088-1-isasmendi.agus@gmail.com

This series was tested with both workarounds under discussion (a lock
around the PCIe reads, and the L2 cache off through the device tree)
with the same results.

Results on a ZTE ZXHN H3600 (MT7915 as AP, a phone as client, flowtable
with lan, wan and the AP interface, NAT on wan):

  WAN -> WiFi download     393 Mbps offloaded, 109 Mbps on the CPU path
  WiFi -> WAN upload       186 Mbps (capped by the upload server), 60
  30 min soak              111 transfers, none failed, ring counters
                           consistent, kernel log clean
  cold / warm boot gate    17/17 and 5/5 boots, offloaded traffic on
                           each, no hang

IPv6 flows are not offloaded, as in the base driver.  The register
sequence and descriptor layout were reverse engineered from the
vendor's GPL kernel.  Builds without warnings with W=1 (board config
and multi_v7_defconfig); checkpatch --strict, dt_binding_check and
dtbs_check are clean.

Agustin Santiago Isasmendi (5):
  dt-bindings: net: zte,zx279128s-gmac: add the WLAN DMA interrupt
  ARM: dts: zte: zx279128s: add the WLAN DMA interrupt
  net: ethernet: zte: zx279128s: WLAN DMA ring and logical ports
  net: ethernet: zte: zx279128s: offload flows to and from WLAN ports
  net: ethernet: zte: zx279128s: debugfs knobs for the WLAN ring

 .../bindings/net/zte,zx279128s-gmac.yaml      |  20 +-
 arch/arm/boot/dts/zte/zx279128s.dtsi          |   4 +-
 drivers/net/ethernet/zte/Kconfig              |   5 +-
 drivers/net/ethernet/zte/Makefile             |   3 +-
 drivers/net/ethernet/zte/zx279128s-eth.h      | 124 ++-
 drivers/net/ethernet/zte/zx279128s-main.c     |  18 +-
 drivers/net/ethernet/zte/zx279128s-ppe.c      |  92 +-
 drivers/net/ethernet/zte/zx279128s-wlan.c     | 874 ++++++++++++++++++
 8 files changed, 1114 insertions(+), 26 deletions(-)
 create mode 100644 drivers/net/ethernet/zte/zx279128s-wlan.c


base-commit: 96b4b72978e9fcfdd74f809c159f26813995631b
-- 
2.30.2