[Patch net-next v1 09/12] net: dsa: microchip: ptp: move pdelay_rsp correction field to tail tag

[Arun Ramadoss <arun.ramadoss@microchip.com>]

From: Christian Eggers <ceggers@arri.de>

For PDelay_Resp messages we will likely have a negative value in the
correction field. The switch hardware cannot correctly update such
values (produces an off by one error in the UDP checksum), so it must be
moved to the time stamp field in the tail tag. Format of the correction
field is 48 bit ns + 16 bit fractional ns.  After updating the
correction field, clone is no longer required hence it is freed.

Signed-off-by: Christian Eggers <ceggers@arri.de>
---
RFC v3 -> Patch v1
- Patch is separated from transmission logic patch
---
 drivers/net/dsa/microchip/ksz_ptp.c |  3 +++
 include/linux/dsa/ksz_common.h      |  2 ++
 net/dsa/tag_ksz.c                   | 42 ++++++++++++++++++++++++++++-
 3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/microchip/ksz_ptp.c b/drivers/net/dsa/microchip/ksz_ptp.c
index 5eb5aca92556..f0b7fcca045b 100644
--- a/drivers/net/dsa/microchip/ksz_ptp.c
+++ b/drivers/net/dsa/microchip/ksz_ptp.c
@@ -182,6 +182,7 @@ void ksz_port_txtstamp(struct dsa_switch *ds, int port,
 
 	switch (ptp_msg_type) {
 	case PTP_MSGTYPE_PDELAY_REQ:
+	case PTP_MSGTYPE_PDELAY_RESP:
 		break;
 
 	default:
@@ -194,6 +195,8 @@ void ksz_port_txtstamp(struct dsa_switch *ds, int port,
 
 	/* caching the value to be used in later */
 	KSZ_SKB_CB(skb)->clone = clone;
+	KSZ_SKB_CB(clone)->ptp_type = type;
+	KSZ_SKB_CB(clone)->ptp_msg_type = ptp_msg_type;
 }
 
 static int _ksz_ptp_gettime(struct ksz_device *dev, struct timespec64 *ts)
diff --git a/include/linux/dsa/ksz_common.h b/include/linux/dsa/ksz_common.h
index 5f0e0c614e94..370ce9b56902 100644
--- a/include/linux/dsa/ksz_common.h
+++ b/include/linux/dsa/ksz_common.h
@@ -38,6 +38,8 @@ struct ksz_tagger_data {
 
 struct ksz_skb_cb {
 	struct sk_buff *clone;
+	unsigned int ptp_type;
+	u8 ptp_msg_type;
 };
 
 #define KSZ_SKB_CB(skb) \
diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index 6ed94dc0f18e..2a08e48f41f8 100644
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -241,14 +241,54 @@ static void ksz_rcv_timestamp(struct sk_buff *skb, u8 *tag,
 /* Time stamp tag is only inserted if PTP is enabled in hardware. */
 static void ksz_xmit_timestamp(struct dsa_port *dp, struct sk_buff *skb)
 {
+	struct sk_buff *clone = KSZ_SKB_CB(skb)->clone;
 	struct ksz_tagger_private *priv;
+	struct ptp_header *ptp_hdr;
+	unsigned int ptp_type;
+	u32 tstamp_raw = 0;
+	u8 ptp_msg_type;
+	s64 correction;
 
 	priv = ksz_tagger_private(dp->ds);
 
 	if (!test_bit(KSZ_HWTS_EN, &priv->state))
 		return;
 
-	put_unaligned_be32(0, skb_put(skb, KSZ_PTP_TAG_LEN));
+	if (!clone)
+		goto output_tag;
+
+	ptp_type = KSZ_SKB_CB(clone)->ptp_type;
+	if (ptp_type == PTP_CLASS_NONE)
+		goto output_tag;
+
+	ptp_hdr = ptp_parse_header(skb, ptp_type);
+	if (!ptp_hdr)
+		goto output_tag;
+
+	ptp_msg_type = KSZ_SKB_CB(clone)->ptp_msg_type;
+	if (ptp_msg_type != PTP_MSGTYPE_PDELAY_RESP)
+		goto output_tag;
+
+	correction = (s64)get_unaligned_be64(&ptp_hdr->correction);
+
+	if (correction < 0) {
+		struct timespec64 ts;
+
+		ts = ns_to_timespec64(-correction >> 16);
+		tstamp_raw = ((ts.tv_sec & 3) << 30) | ts.tv_nsec;
+
+		/* Set correction field to 0 and update UDP checksum.  */
+		ptp_header_update_correction(skb, ptp_type, ptp_hdr, 0);
+	}
+
+	/* For PDelay_Resp messages, the clone is not required in
+	 * skb_complete_tx_timestamp() and should be freed here.
+	 */
+	kfree_skb(clone);
+	KSZ_SKB_CB(skb)->clone = NULL;
+
+output_tag:
+	put_unaligned_be32(tstamp_raw, skb_put(skb, KSZ_PTP_TAG_LEN));
 }
 
 /* Defer transmit if waiting for egress time stamp is required.  */
-- 
2.36.1