netdev - [PATCH 3/3] net: macb: add support for padding and fcs computation

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Date:   Tue, 7 Aug 2018 12:25:14 +0300
From:   Claudiu Beznea <claudiu.beznea@...rochip.com>
To:     <nicolas.ferre@...rochip.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <harinik@...inx.com>, <jennifer.dahm@...com>,
        <nathan.sullivan@...com>, <rafalo@...ence.com>,
        <harinikatakamlinux@...il.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>
Subject: [PATCH 3/3] net: macb: add support for padding and fcs computation

For packets with computed IP/TCP/UDP checksum there is no need to tell
hardware to recompute it. For such kind of packets hardware expects the
packet to be at least 64 bytes and FCS to be computed.

Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
---
 drivers/net/ethernet/cadence/macb_main.c | 70 ++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 1c12afe4a0ce..c16a4b947688 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -10,6 +10,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 #include <linux/clk.h>
+#include <linux/crc32.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/kernel.h>
@@ -1565,6 +1566,9 @@ static unsigned int macb_tx_map(struct macb *bp,
 		if (i == queue->tx_head) {
 			ctrl |= MACB_BF(TX_LSO, lso_ctrl);
 			ctrl |= MACB_BF(TX_TCP_SEQ_SRC, seq_ctrl);
+			if ((bp->dev->features & NETIF_F_HW_CSUM) &&
+			    skb->ip_summed != CHECKSUM_PARTIAL && !lso_ctrl)
+				ctrl |= MACB_BIT(TX_NOCRC);
 		} else
 			/* Only set MSS/MFS on payload descriptors
 			 * (second or later descriptor)
@@ -1651,6 +1655,67 @@ static inline int macb_clear_csum(struct sk_buff *skb)
 	return 0;
 }
 
+static int macb_pad_and_fcs(struct sk_buff **skb, struct net_device *ndev)
+{
+	bool cloned = skb_cloned(*skb) || skb_header_cloned(*skb);
+	int padlen = ETH_ZLEN - (*skb)->len;
+	int headroom = skb_headroom(*skb);
+	int tailroom = skb_tailroom(*skb);
+	struct sk_buff *nskb;
+	u32 fcs;
+
+	if (!(ndev->features & NETIF_F_HW_CSUM) ||
+	    !((*skb)->ip_summed != CHECKSUM_PARTIAL) ||
+	    skb_shinfo(*skb)->gso_size)	/* Not available for GSO */
+		return 0;
+
+	if (padlen <= 0) {
+		/* FCS could be appeded to tailroom. */
+		if (tailroom >= ETH_FCS_LEN)
+			goto add_fcs;
+		/* FCS could be appeded by moving data to headroom. */
+		else if (!cloned && headroom + tailroom >= ETH_FCS_LEN)
+			padlen = 0;
+		/* No room for FCS, need to reallocate skb. */
+		else
+			padlen = ETH_FCS_LEN - tailroom;
+	} else {
+		/* Add room for FCS. */
+		padlen += ETH_FCS_LEN;
+	}
+
+	if (!cloned && headroom + tailroom >= padlen) {
+		(*skb)->data = memmove((*skb)->head, (*skb)->data, (*skb)->len);
+		skb_set_tail_pointer(*skb, (*skb)->len);
+	} else {
+		nskb = skb_copy_expand(*skb, 0, padlen, GFP_ATOMIC);
+		if (!nskb)
+			return -ENOMEM;
+
+		dev_kfree_skb_any(*skb);
+		*skb = nskb;
+	}
+
+	if (padlen) {
+		if (padlen >= ETH_FCS_LEN)
+			skb_put_zero(*skb, padlen - ETH_FCS_LEN);
+		else
+			skb_trim(*skb, ETH_FCS_LEN - padlen);
+	}
+
+add_fcs:
+	/* set FCS to packet */
+	fcs = crc32_le(~0, (*skb)->data, (*skb)->len);
+	fcs = ~fcs;
+
+	skb_put_u8(*skb, fcs		& 0xff);
+	skb_put_u8(*skb, (fcs >> 8)	& 0xff);
+	skb_put_u8(*skb, (fcs >> 16)	& 0xff);
+	skb_put_u8(*skb, (fcs >> 24)	& 0xff);
+
+	return 0;
+}
+
 static netdev_tx_t macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	u16 queue_index = skb_get_queue_mapping(skb);
@@ -1667,6 +1732,11 @@ static netdev_tx_t macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		return ret;
 	}
 
+	if (macb_pad_and_fcs(&skb, dev)) {
+		dev_kfree_skb_any(skb);
+		return ret;
+	}
+
 	is_lso = (skb_shinfo(skb)->gso_size != 0);
 
 	if (is_lso) {
-- 
2.7.4