Subject: Re: [PATCH RFC net-next v2] net: airoha: Add TCP LRO support

From: Lorenzo Bianconi <[email-masked]>
Date: Tue, 26 May 2026 23:08:14 +0200

> From: Lorenzo Bianconi <[email-masked]>
> Date: Tue, 26 May 2026 08:58:05 +0200
> 
> > Add hardware TCP Large Receive Offload (LRO) support to the airoha_eth
> > driver, leveraging the EN7581/AN7583 SoC's 8 dedicated LRO hardware queues
> > mapped to RX queues 24–31. LRO hw offloading does not support
> > Scatter-Gather (SG) so it is required to increase the page_pool allocation
> > order to 2 for RX queues 24–31 (LRO queues).
> > 
> > Performance comparison between GRO and hw LRO has been carried out using
> > a 10Gbps NIC:
> > 
> > GRO: ~2.7 Gbps
> > LRO: ~8.1 Gbps
> > 
> > Please note with respect to the previous implementation, page_pool
> > allocation order has been reduced from 5 to 2.
> > 
> > Tested-by: Madhur Agrawal <[email-masked]>
> > Signed-off-by: Lorenzo Bianconi <[email-masked]>
> 
> [...]
> 
> > @@ -587,6 +630,85 @@ static int airoha_qdma_get_gdm_port(struct airoha_eth *eth,
> >  	return port >= ARRAY_SIZE(eth->ports) ? -EINVAL : port;
> >  }
> >  
> > +static int airoha_qdma_lro_rx_process(struct airoha_queue *q,
> > +				      struct airoha_qdma_desc *desc)
> > +{
> > +	u32 desc_ctrl = le32_to_cpu(READ_ONCE(desc->ctrl));
> > +	u32 msg1 = le32_to_cpu(READ_ONCE(desc->msg1));
> > +	u32 msg2 = le32_to_cpu(READ_ONCE(desc->msg2));
> > +	u32 msg3 = le32_to_cpu(READ_ONCE(desc->msg3));
> 
> Why are these READ_ONCE()s needed? Does desc come from the HW (sorry I
> didn't follow the whole code flow) or...?

Correct, ctrl, msg1, msg2 and msg3 are subfields of the DMA descriptor read by
airoha_qdma_rx_process() from the NIC. I guess here we have a similar issue as
the one fixed in [0]

[0] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=4ae0604a0673e11e2075b178387151fcad5111b5

> 
> > +	struct sk_buff *skb = q->skb;
> > +	u32 len, th_off, tcp_ack_seq;
> > +	u16 tcp_win, l2_len;
> > +	struct tcphdr *th;
> > +	bool ipv4, ipv6;
> > +
> > +	if (FIELD_GET(QDMA_ETH_RXMSG_AGG_COUNT_MASK, msg2) <= 1)
> > +		return 0;
> > +
> > +	ipv4 = FIELD_GET(QDMA_ETH_RXMSG_IP4_MASK, msg1);
> > +	ipv6 = FIELD_GET(QDMA_ETH_RXMSG_IP6_MASK, msg1);
> > +	if (!ipv4 && !ipv6)
> > +		return -EOPNOTSUPP;
> > +
> > +	l2_len = FIELD_GET(QDMA_ETH_RXMSG_L2_LEN_MASK, msg2);
> > +	len = FIELD_GET(QDMA_DESC_LEN_MASK, desc_ctrl);
> > +	if (ipv4) {
> > +		struct iphdr *iph;
> > +
> > +		if (!pskb_may_pull(skb, l2_len + sizeof(*iph)))
> > +			return -EINVAL;
> > +
> > +		iph = (struct iphdr *)(skb->data + l2_len);
> > +		if (iph->protocol != IPPROTO_TCP)
> > +			return -EOPNOTSUPP;
> > +
> > +		iph->tot_len = cpu_to_be16(len - l2_len);
> > +		iph->check = 0;
> > +		iph->check = ip_fast_csum((void *)iph, iph->ihl);
> > +		th_off = l2_len + (iph->ihl << 2);
> > +	} else {
> > +		struct ipv6hdr *ip6h;
> > +
> > +		if (!pskb_may_pull(skb, l2_len + sizeof(*ip6h)))
> > +			return -EINVAL;
> > +
> > +		ip6h = (struct ipv6hdr *)(skb->data + l2_len);
> > +		if (ip6h->nexthdr != NEXTHDR_TCP)
> > +			return -EOPNOTSUPP;
> > +
> > +		ip6h->payload_len = cpu_to_be16(len - l2_len - sizeof(*ip6h));
> > +		th_off = l2_len + sizeof(*ip6h);
> > +	}
> > +
> > +	tcp_win = FIELD_GET(QDMA_ETH_RXMSG_TCP_WIN_MASK, msg3);
> > +	tcp_ack_seq = le32_to_cpu(READ_ONCE(desc->data));
> > +
> > +	if (!pskb_may_pull(skb, th_off + sizeof(*th)))
> > +		return -EINVAL;
> > +
> > +	th = (struct tcphdr *)(skb->data + th_off);
> > +	th->ack_seq = cpu_to_be32(tcp_ack_seq);
> > +	th->window = cpu_to_be16(tcp_win);
> > +
> > +	/* Check tcp timestamp option */
> > +	if (th->doff == (sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4) {
> > +		__be32 *topt = (__be32 *)(th + 1);
> 
> Make sure you checked the code with sparse (sometimes it's needed to
> mark casts as __force, not this one tho)

$ make C=2 CHECK=sparse drivers/net/ethernet/airoha/
  CHECK   scripts/mod/empty.c
  DESCEND objtool
  INSTALL libsubcmd_headers
  DESCEND bpf/resolve_btfids
  INSTALL libsubcmd_headers
  CHECK   drivers/net/ethernet/airoha/airoha_eth.c
  CHECK   drivers/net/ethernet/airoha/airoha_ppe.c
  CHECK   drivers/net/ethernet/airoha/airoha_ppe_debugfs.c
  CHECK   drivers/net/ethernet/airoha/airoha_npu.c

$ sparse --version
v0.6.5-rc1

> 
> > +
> > +		if (*topt == cpu_to_be32((TCPOPT_NOP << 24) |
> 
> Shouldn't this be `((u32)TCPOPT_NOP) << 24` to avoid sign issues?

I guess this is same approach used in [1]. Am I missing something?

[1] https://github.com/torvalds/linux/blob/master/net/ipv4/tcp_ipv4.c#L823

Regards,
Lorenzo

> 
> > +					 (TCPOPT_NOP << 16) |
> > +					 (TCPOPT_TIMESTAMP << 8) |
> > +					 TCPOLEN_TIMESTAMP)) {
> > +			__le32 tcp_ts_reply = READ_ONCE(desc->tcp_ts_reply);
> > +
> > +			put_unaligned_be32(le32_to_cpu(tcp_ts_reply),
> > +					   topt + 2);
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> Thanks,
> Olek