gianfar: Fix invalid TX frames returned on error queue when time stamping

When TX time stamping for PTP messages is enabled on a socket, a time
stamp is returned on the socket error queue to the user space application
after the frame was transmitted. The transmitted frame is also returned on
the error queue so that an application knows to which frame the time stamp
belongs.

In the current implementation the TxFCB is immediately followed by the
frame. Since the eTSEC inserts the TX time stamp 8 bytes after the TxFCB,
parts of the frame have been overwritten and an invalid frame was returned
on the socket error queue.

This patch fixes the described problem by adding additional 16 padding
bytes between the TxFCB and the frame for all messages sent from a time
stamping enabled socket (other sockets are not affected).

Signed-off-by: Manfred Rudigier <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/freescale/gianfar.c

···
 	return fcb;
 }
 
-static inline void gfar_tx_checksum(struct sk_buff *skb, struct txfcb *fcb)
+static inline void gfar_tx_checksum(struct sk_buff *skb, struct txfcb *fcb,
+		int fcb_length)
 {
 	u8 flags = 0;
 
···
 	 * frame (skb->data) and the start of the IP hdr.
 	 * l4os is the distance between the start of the
 	 * l3 hdr and the l4 hdr */
-	fcb->l3os = (u16)(skb_network_offset(skb) - GMAC_FCB_LEN);
+	fcb->l3os = (u16)(skb_network_offset(skb) - fcb_length);
 	fcb->l4os = skb_network_header_len(skb);
 
 	fcb->flags = flags;
···
 	int i, rq = 0, do_tstamp = 0;
 	u32 bufaddr;
 	unsigned long flags;
-	unsigned int nr_frags, nr_txbds, length;
+	unsigned int nr_frags, nr_txbds, length, fcb_length = GMAC_FCB_LEN;
 
 	/*
 	 * TOE=1 frames larger than 2500 bytes may see excess delays
···
 
 	/* check if time stamp should be generated */
 	if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP &&
-		     priv->hwts_tx_en))
+			priv->hwts_tx_en)) {
 		do_tstamp = 1;
+		fcb_length = GMAC_FCB_LEN + GMAC_TXPAL_LEN;
+	}
 
 	/* make space for additional header when fcb is needed */
 	if (((skb->ip_summed == CHECKSUM_PARTIAL) ||
 			vlan_tx_tag_present(skb) ||
 			unlikely(do_tstamp)) &&
-			(skb_headroom(skb) < GMAC_FCB_LEN)) {
+			(skb_headroom(skb) < fcb_length)) {
 		struct sk_buff *skb_new;
 
-		skb_new = skb_realloc_headroom(skb, GMAC_FCB_LEN);
+		skb_new = skb_realloc_headroom(skb, fcb_length);
 		if (!skb_new) {
 			dev->stats.tx_errors++;
 			kfree_skb(skb);
···
 		lstatus = txbdp_start->lstatus;
 	}
 
+	/* Add TxPAL between FCB and frame if required */
+	if (unlikely(do_tstamp)) {
+		skb_push(skb, GMAC_TXPAL_LEN);
+		memset(skb->data, 0, GMAC_TXPAL_LEN);
+	}
+
 	/* Set up checksumming */
 	if (CHECKSUM_PARTIAL == skb->ip_summed) {
 		fcb = gfar_add_fcb(skb);
···
 			skb_checksum_help(skb);
 		} else {
 			lstatus |= BD_LFLAG(TXBD_TOE);
-			gfar_tx_checksum(skb, fcb);
+			gfar_tx_checksum(skb, fcb, fcb_length);
 		}
 	}
 
···
 	 * the full frame length.
 	 */
 	if (unlikely(do_tstamp)) {
-		txbdp_tstamp->bufPtr = txbdp_start->bufPtr + GMAC_FCB_LEN;
+		txbdp_tstamp->bufPtr = txbdp_start->bufPtr + fcb_length;
 		txbdp_tstamp->lstatus |= BD_LFLAG(TXBD_READY) |
-				(skb_headlen(skb) - GMAC_FCB_LEN);
+				(skb_headlen(skb) - fcb_length);
 		lstatus |= BD_LFLAG(TXBD_CRC | TXBD_READY) | GMAC_FCB_LEN;
 	} else {
 		lstatus |= BD_LFLAG(TXBD_CRC | TXBD_READY) | skb_headlen(skb);
···
 
 		if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS)) {
 			next = next_txbd(bdp, base, tx_ring_size);
-			buflen = next->length + GMAC_FCB_LEN;
+			buflen = next->length + GMAC_FCB_LEN + GMAC_TXPAL_LEN;
 		} else
 			buflen = bdp->length;
 
···
 			u64 *ns = (u64*) (((u32)skb->data + 0x10) & ~0x7);
 			memset(&shhwtstamps, 0, sizeof(shhwtstamps));
 			shhwtstamps.hwtstamp = ns_to_ktime(*ns);
+			skb_pull(skb, GMAC_FCB_LEN + GMAC_TXPAL_LEN);
 			skb_tstamp_tx(skb, &shhwtstamps);
 			bdp->lstatus &= BD_LFLAG(TXBD_WRAP);
 			bdp = next;

drivers/net/ethernet/freescale/gianfar.h

···
 /* Length for FCB */
 #define GMAC_FCB_LEN 8
 
+/* Length for TxPAL */
+#define GMAC_TXPAL_LEN 16
+
 /* Default padding amount */
 #define DEFAULT_PADDING 2