[PATCH net-next v3 4/6] ptp: Support late timestamp determination

[Gerhard Engleder <gerhard@engleder-embedded.com>]

If a physical clock supports a free running cycle counter, then
timestamps shall be based on this time too. For TX it is known in
advance before the transmission if a timestamp based on the free running
cycle counter is needed. For RX it is impossible to know which timestamp
is needed before the packet is received and assigned to a socket.

Support late timestamp determination by a network device. Therefore, an
address/cookie is stored within the new netdev_data field of struct
skb_shared_hwtstamps. This address/cookie is provided to a new network
device function called ndo_get_tstamp(), which returns a timestamp based
on the normal/adjustable time or based on the free running cycle
counter. If function is not supported, then timestamp handling is not
changed.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
---
 include/linux/netdevice.h | 21 ++++++++++++++++++++
 include/linux/skbuff.h    | 16 ++++++++++++---
 net/socket.c              | 42 +++++++++++++++++++++++++++++----------
 3 files changed, 66 insertions(+), 13 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4aba92a4042a..47dca9adfb17 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1356,6 +1356,12 @@ struct netdev_net_notifier {
  *	The caller must be under RCU read context.
  * int (*ndo_fill_forward_path)(struct net_device_path_ctx *ctx, struct net_device_path *path);
  *     Get the forwarding path to reach the real device from the HW destination address
+ * ktime_t (*ndo_get_tstamp)(struct net_device *dev,
+ *			     const struct skb_shared_hwtstamps *hwtstamps,
+ *			     bool cycles);
+ *	Get hardware timestamp based on normal/adjustable time or free running
+ *	cycle counter. This function is required if physical clock supports a
+ *	free running cycle counter.
  */
 struct net_device_ops {
 	int			(*ndo_init)(struct net_device *dev);
@@ -1578,6 +1584,9 @@ struct net_device_ops {
 	struct net_device *	(*ndo_get_peer_dev)(struct net_device *dev);
 	int                     (*ndo_fill_forward_path)(struct net_device_path_ctx *ctx,
                                                          struct net_device_path *path);
+	ktime_t			(*ndo_get_tstamp)(struct net_device *dev,
+						  const struct skb_shared_hwtstamps *hwtstamps,
+						  bool cycles);
 };
 
 /**
@@ -4738,6 +4747,18 @@ static inline void netdev_rx_csum_fault(struct net_device *dev,
 void net_enable_timestamp(void);
 void net_disable_timestamp(void);
 
+static inline ktime_t netdev_get_tstamp(struct net_device *dev,
+					const struct skb_shared_hwtstamps *hwtstamps,
+					bool cycles)
+{
+	const struct net_device_ops *ops = dev->netdev_ops;
+
+	if (ops->ndo_get_tstamp)
+		return ops->ndo_get_tstamp(dev, hwtstamps, cycles);
+
+	return hwtstamps->hwtstamp;
+}
+
 static inline netdev_tx_t __netdev_start_xmit(const struct net_device_ops *ops,
 					      struct sk_buff *skb, struct net_device *dev,
 					      bool more)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index fa03e02b761d..732b995fe54e 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -588,8 +588,10 @@ static inline bool skb_frag_must_loop(struct page *p)
 
 /**
  * struct skb_shared_hwtstamps - hardware time stamps
- * @hwtstamp:	hardware time stamp transformed into duration
- *		since arbitrary point in time
+ * @hwtstamp:		hardware time stamp transformed into duration
+ *			since arbitrary point in time
+ * @netdev_data:	address/cookie of network device driver used as
+ *			reference to actual hardware time stamp
  *
  * Software time stamps generated by ktime_get_real() are stored in
  * skb->tstamp.
@@ -601,7 +603,10 @@ static inline bool skb_frag_must_loop(struct page *p)
  * &skb_shared_info. Use skb_hwtstamps() to get a pointer.
  */
 struct skb_shared_hwtstamps {
-	ktime_t	hwtstamp;
+	union {
+		ktime_t	hwtstamp;
+		void *netdev_data;
+	};
 };
 
 /* Definitions for tx_flags in struct skb_shared_info */
@@ -620,6 +625,11 @@ enum {
 	 */
 	SKBTX_HW_TSTAMP_USE_CYCLES = 1 << 3,
 
+	/* determine hardware time stamp based on time or cycles, flag is used
+	 * only for RX path
+	 */
+	SKBTX_HW_TSTAMP_NETDEV = 1 << 3,
+
 	/* generate wifi status information (where possible) */
 	SKBTX_WIFI_STATUS = 1 << 4,
 
diff --git a/net/socket.c b/net/socket.c
index 0f680c7d968a..ee81e25e9b98 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -805,7 +805,8 @@ static bool skb_is_swtx_tstamp(const struct sk_buff *skb, int false_tstamp)
 	return skb->tstamp && !false_tstamp && skb_is_err_queue(skb);
 }
 
-static void put_ts_pktinfo(struct msghdr *msg, struct sk_buff *skb)
+static void put_ts_pktinfo(struct msghdr *msg, struct sk_buff *skb,
+			   int if_index)
 {
 	struct scm_ts_pktinfo ts_pktinfo;
 	struct net_device *orig_dev;
@@ -815,11 +816,15 @@ static void put_ts_pktinfo(struct msghdr *msg, struct sk_buff *skb)
 
 	memset(&ts_pktinfo, 0, sizeof(ts_pktinfo));
 
-	rcu_read_lock();
-	orig_dev = dev_get_by_napi_id(skb_napi_id(skb));
-	if (orig_dev)
-		ts_pktinfo.if_index = orig_dev->ifindex;
-	rcu_read_unlock();
+	if (if_index == -1) {
+		rcu_read_lock();
+		orig_dev = dev_get_by_napi_id(skb_napi_id(skb));
+		if (orig_dev)
+			ts_pktinfo.if_index = orig_dev->ifindex;
+		rcu_read_unlock();
+	} else {
+		ts_pktinfo.if_index = if_index;
+	}
 
 	ts_pktinfo.pkt_length = skb->len - skb_mac_offset(skb);
 	put_cmsg(msg, SOL_SOCKET, SCM_TIMESTAMPING_PKTINFO,
@@ -839,6 +844,8 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
 	int empty = 1, false_tstamp = 0;
 	struct skb_shared_hwtstamps *shhwtstamps =
 		skb_hwtstamps(skb);
+	struct net_device *orig_dev;
+	int if_index = -1;
 	ktime_t hwtstamp;
 
 	/* Race occurred between timestamp enabling and packet
@@ -887,18 +894,33 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
 	if (shhwtstamps &&
 	    (sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) &&
 	    !skb_is_swtx_tstamp(skb, false_tstamp)) {
+		if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_NETDEV) {
+			rcu_read_lock();
+			orig_dev = dev_get_by_napi_id(skb_napi_id(skb));
+			if (orig_dev) {
+				if_index = orig_dev->ifindex;
+				hwtstamp = netdev_get_tstamp(orig_dev,
+							     shhwtstamps,
+							     sk->sk_tsflags &
+							     SOF_TIMESTAMPING_BIND_PHC);
+			} else {
+				hwtstamp = shhwtstamps->hwtstamp;
+			}
+			rcu_read_unlock();
+		} else {
+			hwtstamp = shhwtstamps->hwtstamp;
+		}
+
 		if (sk->sk_tsflags & SOF_TIMESTAMPING_BIND_PHC)
-			hwtstamp = ptp_convert_timestamp(&shhwtstamps->hwtstamp,
+			hwtstamp = ptp_convert_timestamp(&hwtstamp,
 							 sk->sk_bind_phc);
-		else
-			hwtstamp = shhwtstamps->hwtstamp;
 
 		if (ktime_to_timespec64_cond(hwtstamp, tss.ts + 2)) {
 			empty = 0;
 
 			if ((sk->sk_tsflags & SOF_TIMESTAMPING_OPT_PKTINFO) &&
 			    !skb_is_err_queue(skb))
-				put_ts_pktinfo(msg, skb);
+				put_ts_pktinfo(msg, skb, if_index);
 		}
 	}
 	if (!empty) {
-- 
2.20.1