[PATCH net-next v6] net: airoha: add LRO offload support
netdev-bot+sashiko at kernel.org
netdev-bot+sashiko at kernel.org
Tue Sep 8 23:36:37 PDT 2026
Thank you for your contribution! Sashiko AI review found 4 potential
issue(s) to consider:
Critical: 0 · High: 0 · Medium: 1 · Low: 3
- [Medium] The new LRO drop path in `airoha_qdma_rx_process()` increments
`netdev->stats.rx_dropped` (the legacy `struct net_device_stats`…
- [Low] The commit message claims "aggregated skbs are marked
SKB_GSO_DODGY so that the stack does not rely on gso_size and does not…
- [Low] Teardown asymmetry for the shared FE/CDM LRO state:
`airoha_dev_set_features()` arms the per-QDMA LRO block via…
- [Low] The new LRO error path performs a plain, non-atomic read-modify-
write of the shared per-netdev counter `netdev->stats.rx_dropped++`…
--
net: airoha: add LRO offload support
This adds LRO offload to airoha_eth using the 8 dedicated LRO hardware
queues mapped to RX queues 24-31, bumping those queues' page_pool order
since LRO cannot use scatter-gather. Aggregated skbs get GSO metadata
and a pseudo-header checksum so forwarded traffic can be re-segmented,
and NETIF_F_LRO is only offered while a single device uses the QDMA.
Link: https://lore.kernel.org/r/20260831-airoha-eth-lro-v5-1-6b0f50401121@kernel.org
A few questions below.
> diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c
> index 64619e9a704dd..7035b269a7c34 100644
> --- a/drivers/net/ethernet/airoha/airoha_eth.c
> +++ b/drivers/net/ethernet/airoha/airoha_eth.c
[ ... ]
> @@ -657,13 +742,146 @@ airoha_qdma_get_gdm_dev(struct airoha_eth *eth, struct airoha_qdma_desc *desc)
> return port->devs[d] ? port->devs[d] : ERR_PTR(-ENODEV);
> }
>
> +static int airoha_qdma_lro_rx_skb(struct airoha_queue *q,
> + struct airoha_qdma_desc *desc,
> + u32 msg1, u32 len)
> +{
[ ... ]
> + shinfo = skb_shinfo(skb);
> + shinfo->gso_type = ipv4 ? SKB_GSO_TCPV4 : SKB_GSO_TCPV6;
> + shinfo->gso_type |= SKB_GSO_DODGY;
> + shinfo->gso_size = DIV_ROUND_UP(len - data_off, agg_count);
> + shinfo->gso_segs = agg_count;
[Severity: Low]
Is the commit message description of SKB_GSO_DODGY the right way round?
It says:
"aggregated skbs are marked SKB_GSO_DODGY so that the stack does not
rely on gso_size and does not merge the aggregate into the GRO
engine"
SKB_GSO_DODGY means the opposite for gso_segs: it tells the stack that
gso_segs is untrusted and must be recomputed from gso_size. In
qdisc_pkt_len_segs_init() in net/core/dev.c:
if (unlikely(shinfo->gso_type & SKB_GSO_DODGY)) {
int payload = skb->len - hdr_len;
...
gso_segs = DIV_ROUND_UP(payload, shinfo->gso_size);
and the TCP GSO output path uses gso_size as the MSS when re-segmenting,
so the approximated gso_size is authoritative rather than advisory.
The scheme still looks workable, since DIV_ROUND_UP(sum, agg_count) can
never exceed the largest merged segment and the re-segmented packets only
come out smaller. Could the commit message state that rationale instead
of saying the stack does not rely on gso_size?
[ ... ]
> @@ -707,9 +927,17 @@ static int airoha_qdma_rx_process(struct airoha_queue *q, int budget)
> __skb_put(q->skb, len);
> skb_mark_for_recycle(q->skb);
> q->skb->dev = netdev;
> - q->skb->protocol = eth_type_trans(q->skb, netdev);
> q->skb->ip_summed = CHECKSUM_UNNECESSARY;
> skb_record_rx_queue(q->skb, qid);
> +
> + if (airoha_qdma_lro_rx_skb(q, desc, msg1, len)) {
> + netdev->stats.rx_dropped++;
^^^^^^^^^^^^^^^^^^^^^^^^^
[Severity: Medium]
Does this counter ever reach userspace? This driver registers
.ndo_get_stats64 = airoha_dev_get_stats64, and that callback assigns
rx_dropped from its own MIB-derived stats:
storage->rx_dropped = dev->stats.rx_drops;
dev_get_stats() in net/core/dev.c memsets storage and calls
ndo_get_stats64 when it exists, only falling back to
netdev_stats_to_stats64(storage, &dev->stats) when there is no
ndo_get_stats64/ndo_get_stats, and afterwards only adds dev->core_stats.
So every packet dropped here (agg_count above
AIROHA_RXQ_LRO_MAX_AGG_COUNT, IPv6 with extension headers so nexthdr is
not NEXTHDR_TCP, iph->ihl below 5, th->doff below 5, or a frame shorter
than the headers) appears nowhere in ip -s link or rtnetlink.
Would dev_core_stats_rx_dropped_inc(netdev), or the driver's own
dev->stats.rx_drops under its u64_stats syncp, be the better sink here?
[Severity: Low]
Separately, can this increment lose counts? netdev->stats.rx_dropped is
a plain unsigned long shared per netdev, and this is a non-atomic
read-modify-write from NAPI context.
Each RX ring has its own NAPI instance (q->napi, 32 rings across the IRQ
banks) and the target netdev is resolved per descriptor by
airoha_qdma_get_gdm_dev(), so two pollers on different CPUs, for example
LRO rings 24 and 31 both resolving to the same airoha_gdm_dev, can reach:
airoha_qdma_rx_napi_poll()
airoha_qdma_rx_process()
netdev->stats.rx_dropped++;
concurrently with no lock and no per-CPU separation, which also tears on
32-bit.
> + dev_kfree_skb(q->skb);
> + q->skb = NULL;
> + continue;
> + }
> +
> + q->skb->protocol = eth_type_trans(q->skb, netdev);
> } else { /* scattered frame */
> struct skb_shared_info *shinfo = skb_shinfo(q->skb);
> int nr_frags = shinfo->nr_frags;
[ ... ]
> @@ -2288,6 +2582,32 @@ int airoha_get_fe_port(struct airoha_gdm_dev *dev)
> }
> }
>
> +static netdev_features_t airoha_dev_fix_features(struct net_device *netdev,
> + netdev_features_t features)
> +{
> + struct airoha_gdm_dev *dev = netdev_priv(netdev);
> + struct airoha_qdma *qdma;
> +
> + qdma = airoha_qdma_deref(dev);
> + if (qdma->users > 1)
> + features &= ~NETIF_F_LRO;
> +
> + return features;
> +}
> +
> +static int airoha_dev_set_features(struct net_device *netdev,
> + netdev_features_t features)
> +{
> + struct airoha_gdm_dev *dev = netdev_priv(netdev);
> +
> + if (features & NETIF_F_LRO)
> + airoha_dev_lro_enable(dev);
> + else
> + airoha_dev_lro_disable(dev);
> +
> + return 0;
> +}
[Severity: Low]
Should the enable path here be gated on netif_running()? There is no
admin-state check, so ethtool -K ethX lro on arms the shared FE/CDM LRO
block of the QDMA while the interface is still down.
The only teardown sites for that hardware state are ndo_stop and a later
ndo_set_features. unregister_netdev() does not call ndo_stop for an
already-closed device, and neither airoha_qdma_cleanup() nor
airoha_hw_cleanup() touches REG_CDM_LRO_EN, REG_CDM_LRO_RXQ or
REG_CDM_LRO_LIMIT, so after this sequence:
ethtool -K ethX lro on # link down, LRO armed anyway
rmmod airoha_eth
the CDM LRO engine stays enabled and mapped to RX queues 24-31 after
those rings, descriptors and page pools are gone.
This looks like leftover hardware state rather than something worse:
airoha_qdma_cleanup() clears GLOBAL_CFG_RX_DMA_EN_MASK and polls
GLOBAL_CFG_RX_DMA_BUSY_MASK before the RX buffers are released, so no DMA
into freed pages, and airoha_hw_init() asserts and deasserts the fe reset
on the next probe before airoha_fe_init(), so the stale enable bits do not
survive a rebind and cannot make airoha_dev_open() return -EBUSY forever.
Would it make sense to call airoha_dev_lro_disable() from the remove path
as well, so enable and disable are symmetric?
--
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260906-airoha-eth-lro-v6-1-a6cc5179a8c5%40kernel.org
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