linux-kernel - [PATCH] usbnet: smsc95xx: simplify tx

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Date:   Tue,  2 Oct 2018 17:56:02 +0100
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     netdev@...r.kernel.org
Cc:     David.Laight@...LAB.COM, oneukum@...e.com, davem@...emloft.net,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel@...ts.codethink.co.uk,
        Ben Dooks <ben.dooks@...ethink.co.uk>
Subject: [PATCH] usbnet: smsc95xx: simplify tx_fixup code

The smsc95xx_tx_fixup is doing multiple calls to skb_push() to
put an 8-byte command header onto the packet. It would be easier
to do one skb_push() and then copy the data in once the push is
done.

Signed-off-by: Ben Dooks <ben.dooks@...ethink.co.uk>
---
 drivers/net/usb/smsc95xx.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
index cb19aea139d3..813ab93ee2c3 100644
--- a/drivers/net/usb/smsc95xx.c
+++ b/drivers/net/usb/smsc95xx.c
@@ -2006,6 +2006,7 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
 	bool csum = skb->ip_summed == CHECKSUM_PARTIAL;
 	int overhead = csum ? SMSC95XX_TX_OVERHEAD_CSUM : SMSC95XX_TX_OVERHEAD;
 	u32 tx_cmd_a, tx_cmd_b;
+	void *ptr;
 
 	/* We do not advertise SG, so skbs should be already linearized */
 	BUG_ON(skb_shinfo(skb)->nr_frags);
@@ -2019,6 +2020,9 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
 		return NULL;
 	}
 
+	tx_cmd_b = (u32)skb->len;
+	tx_cmd_a = tx_cmd_b | TX_CMD_A_FIRST_SEG_ | TX_CMD_A_LAST_SEG_;
+
 	if (csum) {
 		if (skb->len <= 45) {
 			/* workaround - hardware tx checksum does not work
@@ -2035,21 +2039,18 @@ static struct sk_buff *smsc95xx_tx_fixup(struct usbnet *dev,
 			skb_push(skb, 4);
 			cpu_to_le32s(&csum_preamble);
 			memcpy(skb->data, &csum_preamble, 4);
+
+			tx_cmd_a += 4;
+			tx_cmd_b += 4;
+			tx_cmd_b |= TX_CMD_B_CSUM_ENABLE;
 		}
 	}
 
-	skb_push(skb, 4);
-	tx_cmd_b = (u32)(skb->len - 4);
-	if (csum)
-		tx_cmd_b |= TX_CMD_B_CSUM_ENABLE;
-	cpu_to_le32s(&tx_cmd_b);
-	memcpy(skb->data, &tx_cmd_b, 4);
-
-	skb_push(skb, 4);
-	tx_cmd_a = (u32)(skb->len - 8) | TX_CMD_A_FIRST_SEG_ |
-		TX_CMD_A_LAST_SEG_;
-	cpu_to_le32s(&tx_cmd_a);
-	memcpy(skb->data, &tx_cmd_a, 4);
+	ptr = skb_push(skb, 8);
+	tx_cmd_a = cpu_to_le32(tx_cmd_a);
+	tx_cmd_b = cpu_to_le32(tx_cmd_b);
+	memcpy(ptr, &tx_cmd_a, 4);
+	memcpy(ptr+4, &tx_cmd_b, 4);
 
 	return skb;
 }
-- 
2.19.0