Subject: Re: [PATCH] Gigabit Ethernet driver of Topcliff PCH

From: Stephen Hemminger <[email-masked]>
Date: Thu, 26 Aug 2010 08:57:58 -0700

On Thu, 26 Aug 2010 18:56:55 +0900
Masayuki Ohtake <[email-masked]> wrote:

> +static void pch_gbe_tx_queue(struct pch_gbe_adapter *adapter,
> +		 struct pch_gbe_tx_ring *tx_ring, struct sk_buff *skb)
> +{
> +	struct pch_gbe_hw *hw = &adapter->hw;
> +	struct pch_gbe_tx_desc *tx_desc;
> +	struct pch_gbe_buffer *buffer_info;
> +	struct sk_buff *tmp_skb;
> +	unsigned int frame_ctrl;
> +	unsigned int ring_num;
> +	unsigned long flags;
> +
> +	PCH_GBE_DEBUG("%s\n", __func__);
> +
> +
> +	/*-- Set frame control --*/
> +	frame_ctrl = 0;
> +	if (unlikely(skb->len < PCH_GBE_SHORT_PKT))
> +		frame_ctrl |= PCH_GBE_TXD_CTRL_APAD;
> +	if (unlikely(adapter->tx_csum == FALSE))
> +		frame_ctrl |= PCH_GBE_TXD_CTRL_TCPIP_ACC_OFF;
> +
> +	/* Performs checksum processing */
> +	/*
> +	 * It is because the hardware accelerator does not support a checksum,
> +	 * when the received data size is less than 64 bytes.
> +	 */
> +	if ((skb->len < PCH_GBE_SHORT_PKT) && (adapter->tx_csum == TRUE)) {
> +		frame_ctrl |=
> +			PCH_GBE_TXD_CTRL_APAD | PCH_GBE_TXD_CTRL_TCPIP_ACC_OFF;
> +		if (skb->protocol == htons(ETH_P_IP)) {
> +			struct iphdr *iph = ip_hdr(skb);
> +			unsigned int offset;
> +			iph->check = 0;
> +			iph->check = ip_fast_csum((u8 *) iph, iph->ihl);
> +			offset = skb_transport_offset(skb);
> +			if (iph->protocol == IPPROTO_TCP) {
> +				skb->csum = 0;
> +				tcp_hdr(skb)->check = 0;
> +				skb->csum =
> +					skb_checksum(skb, offset,
> +						skb->len - offset, 0);
> +				tcp_hdr(skb)->check =
> +					csum_tcpudp_magic(iph->saddr,
> +							iph->daddr,
> +							skb->len - offset,
> +							IPPROTO_TCP, skb->csum);
> +			} else if (iph->protocol == IPPROTO_UDP) {
> +				skb->csum = 0;
> +				udp_hdr(skb)->check = 0;
> +				skb->csum =
> +					skb_checksum(skb, offset,
> +						skb->len - offset, 0);
> +				udp_hdr(skb)->check =
> +					csum_tcpudp_magic(iph->saddr,
> +							iph->daddr,
> +							skb->len - offset,
> +							IPPROTO_UDP, skb->csum);
> +			}
> +		}
> +	}

Why not something simpler using skb_checksum_help which is
safer since it handles case of shared skb correctly.

	if (skb->ip_summed = CHECKSUM_COMPLETE &&
            skb->len < PCH_GBE_SHORT_PKT) {
		frame_ctrl |=
			PCH_GBE_TXD_CTRL_APAD | PCH_GBE_TXD_CTRL_TCPIP_ACC_OFF;
		skb->ip_summed = CHECKSUM_NONE;
                if (skb_checksum_help(skb))
                      goto drop;  /* could not expand header to find space */
        }

--