[PATCH net-next v3 2/6] ptp: Request cycles for TX timestamp

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

The free running cycle counter of physical clocks called cycles shall be
used for hardware timestamps to enable synchronisation.

Introduce new flag SKBTX_HW_TSTAMP_USE_CYCLES, which signals driver to
provide a TX timestamp based on cycles if cycles are supported.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
---
 include/linux/skbuff.h |  5 +++++
 net/core/skbuff.c      |  5 +++++
 net/socket.c           | 11 ++++++++++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3270cb72e4d8..fa03e02b761d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -615,6 +615,11 @@ enum {
 	/* device driver is going to provide hardware time stamp */
 	SKBTX_IN_PROGRESS = 1 << 2,
 
+	/* generate hardware time stamp based on cycles if supported, flag is
+	 * used only for TX path
+	 */
+	SKBTX_HW_TSTAMP_USE_CYCLES = 1 << 3,
+
 	/* generate wifi status information (where possible) */
 	SKBTX_WIFI_STATUS = 1 << 4,
 
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b92e93dcaa91..62d6d143dd70 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4841,6 +4841,11 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb,
 		skb_shinfo(skb)->tx_flags |= skb_shinfo(orig_skb)->tx_flags &
 					     SKBTX_ANY_TSTAMP;
 		skb_shinfo(skb)->tskey = skb_shinfo(orig_skb)->tskey;
+	} else {
+		/* Do not clone SKBTX_HW_TSTAMP_USE_CYCLES flag to enable reuse
+		 * of the same bit in RX path.
+		 */
+		skb_shinfo(skb)->tx_flags &= ~SKBTX_HW_TSTAMP_USE_CYCLES;
 	}
 
 	if (hwtstamps)
diff --git a/net/socket.c b/net/socket.c
index f0c39c874665..5c1c5e6100e1 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -683,9 +683,18 @@ void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)
 {
 	u8 flags = *tx_flags;
 
-	if (tsflags & SOF_TIMESTAMPING_TX_HARDWARE)
+	if (tsflags & SOF_TIMESTAMPING_TX_HARDWARE) {
 		flags |= SKBTX_HW_TSTAMP;
 
+		/* PTP hardware clocks can provide a free running cycle counter
+		 * as a time base for virtual clocks. Tell driver to use the
+		 * free running cycle counter for timestamp if socket is bound
+		 * to virtual clock.
+		 */
+		if (tsflags & SOF_TIMESTAMPING_BIND_PHC)
+			flags |= SKBTX_HW_TSTAMP_USE_CYCLES;
+	}
+
 	if (tsflags & SOF_TIMESTAMPING_TX_SOFTWARE)
 		flags |= SKBTX_SW_TSTAMP;
 
-- 
2.20.1