ixgbe: Add ptp work item to poll for the Tx timestamp

This patch copies the igb implementation of Tx timestamps, which uses a work
item to poll for the Tx timestamp. In addition it adds a timeout value of 15
seconds, after which it will stop polling.

This is necessary due to an issue with the descriptor being marked done before
the Tx timestamp event has occurred. These two events don't correlate, so using
the done bit on the descriptor as indication that the timestamp must already
have been taken leads to potentially dropped Tx timestamps (especially under
heavy packet load)
Reported-by: Matthew Vick <matthew.vick@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe.h

@@ -582,6 +582,9 @@ struct ixgbe_adapter {
 
 	struct ptp_clock *ptp_clock;
 	struct ptp_clock_info ptp_caps;
+	struct work_struct ptp_tx_work;
+	struct sk_buff *ptp_tx_skb;
+	unsigned long ptp_tx_start;
 	unsigned long last_overflow_check;
 	unsigned long last_rx_ptp_check;
 	spinlock_t tmreg_lock;
@@ -752,8 +755,6 @@ extern void ixgbe_ptp_init(struct ixgbe_adapter *adapter);
 extern void ixgbe_ptp_stop(struct ixgbe_adapter *adapter);
 extern void ixgbe_ptp_overflow_check(struct ixgbe_adapter *adapter);
 extern void ixgbe_ptp_rx_hang(struct ixgbe_adapter *adapter);
-extern void ixgbe_ptp_tx_hwtstamp(struct ixgbe_q_vector *q_vector,
-				  struct sk_buff *skb);
 extern void ixgbe_ptp_rx_hwtstamp(struct ixgbe_ring *rx_ring,
 				  union ixgbe_adv_rx_desc *rx_desc,
 				  struct sk_buff *skb);

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -850,9 +850,6 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 		total_bytes += tx_buffer->bytecount;
 		total_packets += tx_buffer->gso_segs;
 
-		if (unlikely(tx_buffer->tx_flags & IXGBE_TX_FLAGS_TSTAMP))
-			ixgbe_ptp_tx_hwtstamp(q_vector, tx_buffer->skb);
-
 		/* free the skb */
 		dev_kfree_skb_any(tx_buffer->skb);
 
@@ -5880,7 +5877,6 @@ static void ixgbe_service_task(struct work_struct *work)
 	struct ixgbe_adapter *adapter = container_of(work,
 						     struct ixgbe_adapter,
 						     service_task);
-
 	ixgbe_reset_subtask(adapter);
 	ixgbe_sfp_detection_subtask(adapter);
 	ixgbe_sfp_link_config_subtask(adapter);
@@ -5888,8 +5884,11 @@ static void ixgbe_service_task(struct work_struct *work)
 	ixgbe_watchdog_subtask(adapter);
 	ixgbe_fdir_reinit_subtask(adapter);
 	ixgbe_check_hang_subtask(adapter);
+
+	if (adapter->flags2 & IXGBE_FLAG2_PTP_ENABLED) {
 		ixgbe_ptp_overflow_check(adapter);
 		ixgbe_ptp_rx_hang(adapter);
+	}
 
 	ixgbe_service_event_complete(adapter);
 }
@@ -6435,6 +6434,11 @@ netdev_tx_t ixgbe_xmit_frame_ring(struct sk_buff *skb,
 	if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)) {
 		skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
 		tx_flags |= IXGBE_TX_FLAGS_TSTAMP;
+
+		/* schedule check for Tx timestamp */
+		adapter->ptp_tx_skb = skb_get(skb);
+		adapter->ptp_tx_start = jiffies;
+		schedule_work(&adapter->ptp_tx_work);
 	}
 
 #ifdef CONFIG_PCI_IOV

drivers/net/ethernet/intel/ixgbe/ixgbe_ptp.c

@@ -96,6 +96,7 @@
 #define IXGBE_MAX_TIMEADJ_VALUE  0x7FFFFFFFFFFFFFFFULL
 
 #define IXGBE_OVERFLOW_PERIOD    (HZ * 30)
+#define IXGBE_PTP_TX_TIMEOUT     (HZ * 15)
 
 #ifndef NSECS_PER_SEC
 #define NSECS_PER_SEC 1000000000ULL
@@ -401,7 +402,6 @@ void ixgbe_ptp_check_pps_event(struct ixgbe_adapter *adapter, u32 eicr)
 	}
 }
 
-
 /**
  * ixgbe_ptp_overflow_check - watchdog task to detect SYSTIME overflow
  * @adapter: private adapter struct
@@ -416,8 +416,7 @@ void ixgbe_ptp_overflow_check(struct ixgbe_adapter *adapter)
 					     IXGBE_OVERFLOW_PERIOD);
 	struct timespec ts;
 
-	if ((adapter->flags2 & IXGBE_FLAG2_PTP_ENABLED) &&
-	    (timeout)) {
+	if (timeout) {
 		ixgbe_ptp_gettime(&adapter->ptp_caps, &ts);
 		adapter->last_overflow_check = jiffies;
 	}
@@ -467,48 +466,68 @@ void ixgbe_ptp_rx_hang(struct ixgbe_adapter *adapter)
 
 /**
  * ixgbe_ptp_tx_hwtstamp - utility function which checks for TX time stamp
- * @q_vector: structure containing interrupt and ring information
- * @skb: particular skb to send timestamp with
+ * @adapter: the private adapter struct
  *
  * if the timestamp is valid, we convert it into the timecounter ns
  * value, then store that result into the shhwtstamps structure which
  * is passed up the network stack
  */
-void ixgbe_ptp_tx_hwtstamp(struct ixgbe_q_vector *q_vector,
-			   struct sk_buff *skb)
+static void ixgbe_ptp_tx_hwtstamp(struct ixgbe_adapter *adapter)
 {
-	struct ixgbe_adapter *adapter;
-	struct ixgbe_hw *hw;
+	struct ixgbe_hw *hw = &adapter->hw;
 	struct skb_shared_hwtstamps shhwtstamps;
 	u64 regval = 0, ns;
-	u32 tsynctxctl;
 	unsigned long flags;
 
-	/* we cannot process timestamps on a ring without a q_vector */
-	if (!q_vector || !q_vector->adapter)
-		return;
-
-	adapter = q_vector->adapter;
-	hw = &adapter->hw;
-
-	tsynctxctl = IXGBE_READ_REG(hw, IXGBE_TSYNCTXCTL);
 	regval |= (u64)IXGBE_READ_REG(hw, IXGBE_TXSTMPL);
 	regval |= (u64)IXGBE_READ_REG(hw, IXGBE_TXSTMPH) << 32;
 
-	/*
-	 * if TX timestamp is not valid, exit after clearing the
-	 * timestamp registers
-	 */
-	if (!(tsynctxctl & IXGBE_TSYNCTXCTL_VALID))
-		return;
-
 	spin_lock_irqsave(&adapter->tmreg_lock, flags);
 	ns = timecounter_cyc2time(&adapter->tc, regval);
 	spin_unlock_irqrestore(&adapter->tmreg_lock, flags);
 
 	memset(&shhwtstamps, 0, sizeof(shhwtstamps));
 	shhwtstamps.hwtstamp = ns_to_ktime(ns);
-	skb_tstamp_tx(skb, &shhwtstamps);
+	skb_tstamp_tx(adapter->ptp_tx_skb, &shhwtstamps);
+
+	dev_kfree_skb_any(adapter->ptp_tx_skb);
+	adapter->ptp_tx_skb = NULL;
+}
+
+/**
+ * ixgbe_ptp_tx_hwtstamp_work
+ * @work: pointer to the work struct
+ *
+ * This work item polls TSYNCTXCTL valid bit to determine when a Tx hardware
+ * timestamp has been taken for the current skb. It is necesary, because the
+ * descriptor's "done" bit does not correlate with the timestamp event.
+ */
+static void ixgbe_ptp_tx_hwtstamp_work(struct work_struct *work)
+{
+	struct ixgbe_adapter *adapter = container_of(work, struct ixgbe_adapter,
+						     ptp_tx_work);
+	struct ixgbe_hw *hw = &adapter->hw;
+	bool timeout = time_is_before_jiffies(adapter->ptp_tx_start +
+					      IXGBE_PTP_TX_TIMEOUT);
+	u32 tsynctxctl;
+
+	/* we have to have a valid skb */
+	if (!adapter->ptp_tx_skb)
+		return;
+
+	if (timeout) {
+		dev_kfree_skb_any(adapter->ptp_tx_skb);
+		adapter->ptp_tx_skb = NULL;
+		e_warn(drv, "clearing Tx Timestamp hang");
+		return;
+	}
+
+	tsynctxctl = IXGBE_READ_REG(hw, IXGBE_TSYNCTXCTL);
+	if (tsynctxctl & IXGBE_TSYNCTXCTL_VALID)
+		ixgbe_ptp_tx_hwtstamp(adapter);
+	else
+		/* reschedule to keep checking if it's not available yet */
+		schedule_work(&adapter->ptp_tx_work);
 }
 
 /**
@@ -865,6 +884,7 @@ void ixgbe_ptp_init(struct ixgbe_adapter *adapter)
 	}
 
 	spin_lock_init(&adapter->tmreg_lock);
+	INIT_WORK(&adapter->ptp_tx_work, ixgbe_ptp_tx_hwtstamp_work);
 
 	adapter->ptp_clock = ptp_clock_register(&adapter->ptp_caps,
 						&adapter->pdev->dev);
@@ -896,6 +916,12 @@ void ixgbe_ptp_stop(struct ixgbe_adapter *adapter)
 
 	ixgbe_ptp_setup_sdp(adapter);
 
+	cancel_work_sync(&adapter->ptp_tx_work);
+	if (adapter->ptp_tx_skb) {
+		dev_kfree_skb_any(adapter->ptp_tx_skb);
+		adapter->ptp_tx_skb = NULL;
+	}
+
 	if (adapter->ptp_clock) {
 		ptp_clock_unregister(adapter->ptp_clock);
 		adapter->ptp_clock = NULL;