Re: [RFC] r8169 : why SG / TX checksum are default disabled

[Francois Romieu <romieu@fr.zoreil.com>]

hayeswang <hayeswang@realtek.com> :
[...]
> I find that the total length field of IP header would be modified if the hw
> checksum is enabled. Therefore, skb_padto + hw checksum wouldn't work.

Ok, my patch completely ignored the fact that skb_padto does not change the
length.

However skb_padto + length adjustement + hw checksum should work (at least in
theory if not in the patch below) ?

diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c
index be4e00f..8d0cc09 100644
--- a/drivers/net/ethernet/realtek/r8169.c
+++ b/drivers/net/ethernet/realtek/r8169.c
@@ -5740,7 +5740,7 @@ err_out:
 	return -EIO;
 }
 
-static inline void rtl8169_tso_csum(struct rtl8169_private *tp,
+static inline bool rtl8169_tso_csum(struct rtl8169_private *tp,
 				    struct sk_buff *skb, u32 *opts)
 {
 	const struct rtl_tx_desc_info *info = tx_desc_info + tp->txd_version;
@@ -5753,6 +5753,13 @@ static inline void rtl8169_tso_csum(struct rtl8169_private *tp,
 	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {
 		const struct iphdr *ip = ip_hdr(skb);
 
+		if (unlikely(skb->len < ETH_ZLEN &&
+		    (tp->mac_version == RTL_GIGA_MAC_VER_34))) {
+			if (skb_padto(skb, ETH_ZLEN))
+				return false;
+			skb_put(skb, ETH_ZLEN - skb->len);
+		}
+
 		if (ip->protocol == IPPROTO_TCP)
 			opts[offset] |= info->checksum.tcp;
 		else if (ip->protocol == IPPROTO_UDP)
@@ -5760,6 +5767,7 @@ static inline void rtl8169_tso_csum(struct rtl8169_private *tp,
 		else
 			WARN_ON_ONCE(1);
 	}
+	return true;
 }
 
 static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
@@ -5783,25 +5791,26 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 	if (unlikely(le32_to_cpu(txd->opts1) & DescOwn))
 		goto err_stop_0;
 
+	opts[1] = cpu_to_le32(rtl8169_tx_vlan_tag(tp, skb));
+	opts[0] = DescOwn;
+
+	if (!rtl8169_tso_csum(tp, skb, opts))
+		goto err_update_stats_0;
+
 	len = skb_headlen(skb);
 	mapping = dma_map_single(d, skb->data, len, DMA_TO_DEVICE);
 	if (unlikely(dma_mapping_error(d, mapping))) {
 		if (net_ratelimit())
 			netif_err(tp, drv, dev, "Failed to map TX DMA!\n");
-		goto err_dma_0;
+		goto err_free_skb_1;
 	}
 
 	tp->tx_skb[entry].len = len;
 	txd->addr = cpu_to_le64(mapping);
 
-	opts[1] = cpu_to_le32(rtl8169_tx_vlan_tag(tp, skb));
-	opts[0] = DescOwn;
-
-	rtl8169_tso_csum(tp, skb, opts);
-
 	frags = rtl8169_xmit_frags(tp, skb, opts);
 	if (frags < 0)
-		goto err_dma_1;
+		goto err_unmap_2;
 	else if (frags)
 		opts[0] |= FirstFrag;
 	else {
@@ -5849,10 +5858,11 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	return NETDEV_TX_OK;
 
-err_dma_1:
+err_unmap_2:
 	rtl8169_unmap_tx_skb(d, tp->tx_skb + entry, txd);
-err_dma_0:
+err_free_skb_1:
 	dev_kfree_skb(skb);
+err_update_stats_0:
 	dev->stats.tx_dropped++;
 	return NETDEV_TX_OK;