==============================================================================
First attempt:

/* hard_start_xmit for devices that don't have any bugs and
 * support TG3_FLG2_HW_TSO_2 only.
 */
static int tg3_start_xmit(PacketBuf_s *skb, struct net_device *dev)
{
	struct tg3 *tp = netdev_priv(dev);
	dma_addr_t mapping;
	u32 len, entry, base_flags, mss;

	kerndbg( KERN_DEBUG, "%s(): ENTER\n", __FUNCTION__ );

#if 0
	len = skb_headlen(skb);
#else
	len = skb->pb_nSize;
#endif

	entry = tp->tx_prod;
	base_flags = 0;
	mss = 0;

	/* Queue skb data, a.k.a. the main skb fragment. */
	mapping = pci_map_single(tp->pdev, skb->pb_pData, len, PCI_DMA_TODEVICE);

	tp->tx_buffers[entry].skb = skb;
	//pci_unmap_addr_set(&tp->tx_buffers[entry], mapping, mapping);

	tg3_set_txd(tp, entry, mapping, len, base_flags,
		    (skb->pb_psNext == NULL) | (mss << 1));

	entry = NEXT_TX(entry);

#if 0
	/* Now loop through additional data fragments, and queue them. */
	if (skb_shinfo(skb)->nr_frags > 0) {
		unsigned int i, last;

		last = skb_shinfo(skb)->nr_frags - 1;
		for (i = 0; i <= last; i++) {
			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

			len = frag->size;
			mapping = pci_map_page(tp->pdev,
					       frag->page,
					       frag->page_offset,
					       len, PCI_DMA_TODEVICE);

			tp->tx_buffers[entry].skb = NULL;
			pci_unmap_addr_set(&tp->tx_buffers[entry], mapping, mapping);

			tg3_set_txd(tp, entry, mapping, len,
				    base_flags, (i == last) | (mss << 1));

			entry = NEXT_TX(entry);
		}
	}
#endif
	/* Packets are ready, update Tx producer idx local and on card. */
	tw32_tx_mbox((MAILBOX_SNDHOST_PROD_IDX_0 + TG3_64BIT_REG_LOW), entry);

#if 0
	tp->tx_prod = entry;
	if (tg3_tx_avail(tp) <= (MAX_SKB_FRAGS + 1)) {
		netif_stop_queue(dev);
		if (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH)
			netif_wake_queue(tp->dev);
	}
#endif

out_unlock:
	smp_wmb();

	dev->trans_start = jiffies;

	return 0;
}

==============================================================================
Second attempt:

/* hard_start_xmit for devices that don't have any bugs and
 * support TG3_FLG2_HW_TSO_2 only.
 */
static int tg3_start_xmit(PacketBuf_s *skb, struct net_device *dev)
{
	struct tg3 *tp = netdev_priv(dev);
	dma_addr_t mapping;
	u32 len, entry, base_flags, mss;

	kerndbg( KERN_DEBUG, "%s(): ENTER\n", __FUNCTION__ );

#if 0
	len = skb_headlen(skb);
#else
	len = skb->pb_nSize;
#endif

	entry = tp->tx_prod;
	base_flags = 0;
	mss = 0;

	/* Queue skb data, a.k.a. the main skb fragment. */
	mapping = pci_map_single(tp->pdev, skb->pb_pData, len, PCI_DMA_TODEVICE);

	tp->tx_buffers[entry].skb = skb;
#if 0
	pci_unmap_addr_set(&tp->tx_buffers[entry], mapping, mapping);

	tg3_set_txd(tp, entry, mapping, len, base_flags,
		    (skb->pb_psNext == NULL) | (mss << 1));
#else
	tg3_set_txd(tp, entry, skb->pb_pData, len, base_flags,
		    1 | (mss << 1));
#endif

	entry = NEXT_TX(entry);

#if 0
	/* Now loop through additional data fragments, and queue them. */
	if (skb_shinfo(skb)->nr_frags > 0) {
		unsigned int i, last;

		last = skb_shinfo(skb)->nr_frags - 1;
		for (i = 0; i <= last; i++) {
			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

			len = frag->size;
			mapping = pci_map_page(tp->pdev,
					       frag->page,
					       frag->page_offset,
					       len, PCI_DMA_TODEVICE);

			tp->tx_buffers[entry].skb = NULL;
			pci_unmap_addr_set(&tp->tx_buffers[entry], mapping, mapping);

			tg3_set_txd(tp, entry, mapping, len,
				    base_flags, (i == last) | (mss << 1));

			entry = NEXT_TX(entry);
		}
	}
#endif
	/* Packets are ready, update Tx producer idx local and on card. */
	tw32_tx_mbox((MAILBOX_SNDHOST_PROD_IDX_0 + TG3_64BIT_REG_LOW), entry);

	tp->tx_prod = entry;
#if 0
	if (tg3_tx_avail(tp) <= (MAX_SKB_FRAGS + 1)) {
		netif_stop_queue(dev);
		if (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH)
			netif_wake_queue(tp->dev);
	}
#endif

out_unlock:
	smp_wmb();

	dev->trans_start = jiffies;

	return 0;
}

==============================================================================
Final version:

/* hard_start_xmit for devices that don't have any bugs and
 * support TG3_FLG2_HW_TSO_2 only.
 */
static int tg3_start_xmit(PacketBuf_s *skb, struct net_device *dev)
{
	struct tg3 *tp = netdev_priv(dev);
	u32 len, entry;

	kerndbg( KERN_DEBUG, "%s(): ENTER\n", __FUNCTION__ );

	len = skb->pb_nSize;
	entry = tp->tx_prod;

	tp->tx_buffers[entry].skb = skb;
	tg3_set_txd(tp, entry, (dma_addr_t)skb->pb_pData, len, 0, 1 );

	entry = NEXT_TX(entry);

	/* Packets are ready, update Tx producer idx local and on card. */
	tw32_tx_mbox((MAILBOX_SNDHOST_PROD_IDX_0 + TG3_64BIT_REG_LOW), entry);
	tp->tx_prod = entry;

out_unlock:
	smp_wmb();

	dev->trans_start = jiffies;

	return 0;
}