ice: check Tx timestamp memory register for ready timestamps

The PHY for E822 based hardware has a register which indicates which
timestamps are valid in the PHY timestamp memory block. Each bit in the
register indicates whether the associated index in the timestamp memory is
valid.

Hardware sets this bit when the timestamp is captured, and clears the bit
when the timestamp is read. Use of this register is important as reading
timestamp registers can impact the way that hardware generates timestamp
interrupts.

This occurs because the PHY has an internal value which is incremented
when hardware captures a timestamp and decremented when software reads a
timestamp. Reading timestamps which are not marked as valid still decrement
the internal value and can result in the Tx timestamp interrupt not
triggering in the future.

To prevent this, use the timestamp memory value to determine which
timestamps are ready to be read. The ice_get_phy_tx_tstamp_ready function
reads this value. For E810 devices, this just always returns with all bits
set.

Skip any timestamp which is not set in this bitmap, avoiding reading extra
timestamps on E822 devices.

The stale check against a cached timestamp value is no longer necessary for
PHYs which support the timestamp ready bitmap properly. E810 devices still
need this. Introduce a new verify_cached flag to the ice_ptp_tx structure.
Use this to determine if we need to perform the verification against the
cached timestamp value. Set this to 1 for the E810 Tx tracker init
function. Notice that many of the fields in ice_ptp_tx are simple 1 bit
flags. Save some structure space by using bitfields of length 1 for these
values.

Modify the ICE_PTP_TS_VALID check to simply drop the timestamp immediately
so that in an event of getting such an invalid timestamp the driver does
not attempt to re-read the timestamp again in a future poll of the
register.

With these changes, the driver now reads each timestamp register exactly
once, and does not attempt any re-reads. This ensures the interrupt
tracking logic in the PHY will not get stuck.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

1 files changed, 41 insertions, 7 deletions

diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.c b/drivers/net/ethernet/intel/ice/ice_ptp.c
index 726579c0098c..30061598912b 100644
--- a/drivers/net/ethernet/intel/ice/ice_ptp.c
+++ b/drivers/net/ethernet/intel/ice/ice_ptp.c
@@ -658,6 +658,9 @@ static bool ice_ptp_tx_tstamp(struct ice_ptp_tx *tx)
 	struct ice_ptp_port *ptp_port;
 	bool ts_handled = true;
 	struct ice_pf *pf;
+	struct ice_hw *hw;
+	u64 tstamp_ready;
+	int err;
 	u8 idx;
 
 	if (!tx->init)
@@ -665,6 +668,12 @@ static bool ice_ptp_tx_tstamp(struct ice_ptp_tx *tx)
 
 	ptp_port = container_of(tx, struct ice_ptp_port, tx);
 	pf = ptp_port_to_pf(ptp_port);
+	hw = &pf->hw;
+
+	/* Read the Tx ready status first */
+	err = ice_get_phy_tx_tstamp_ready(hw, tx->block, &tstamp_ready);
+	if (err)
+		return false;
 
 	for_each_set_bit(idx, tx->in_use, tx->len) {
 		struct skb_shared_hwtstamps shhwtstamps = {};
@@ -672,7 +681,6 @@ static bool ice_ptp_tx_tstamp(struct ice_ptp_tx *tx)
 		u64 raw_tstamp = 0, tstamp;
 		bool drop_ts = false;
 		struct sk_buff *skb;
-		int err;
 
 		/* Drop packets which have waited for more than 2 seconds */
 		if (time_is_before_jiffies(tx->tstamps[idx].start + 2 * HZ)) {
@@ -680,27 +688,47 @@ static bool ice_ptp_tx_tstamp(struct ice_ptp_tx *tx)
 
 			/* Count the number of Tx timestamps that timed out */
 			pf->ptp.tx_hwtstamp_timeouts++;
+		}
 
-			goto skip_ts_read;
+		/* Only read a timestamp from the PHY if its marked as ready
+		 * by the tstamp_ready register. This avoids unnecessary
+		 * reading of timestamps which are not yet valid. This is
+		 * important as we must read all timestamps which are valid
+		 * and only timestamps which are valid during each interrupt.
+		 * If we do not, the hardware logic for generating a new
+		 * interrupt can get stuck on some devices.
+		 */
+		if (!(tstamp_ready & BIT_ULL(phy_idx))) {
+			if (drop_ts)
+				goto skip_ts_read;
+
+			continue;
 		}
 
 		ice_trace(tx_tstamp_fw_req, tx->tstamps[idx].skb, idx);
 
-		err = ice_read_phy_tstamp(&pf->hw, tx->block, phy_idx,
-					  &raw_tstamp);
+		err = ice_read_phy_tstamp(hw, tx->block, phy_idx, &raw_tstamp);
 		if (err)
 			continue;
 
 		ice_trace(tx_tstamp_fw_done, tx->tstamps[idx].skb, idx);
 
-		/* Check if the timestamp is invalid or stale */
-		if (!(raw_tstamp & ICE_PTP_TS_VALID) ||
+		/* For PHYs which don't implement a proper timestamp ready
+		 * bitmap, verify that the timestamp value is different
+		 * from the last cached timestamp. If it is not, skip this for
+		 * now assuming it hasn't yet been captured by hardware.
+		 */
+		if (!drop_ts && tx->verify_cached &&
 		    raw_tstamp == tx->tstamps[idx].cached_tstamp)
 			continue;
 
+		/* Discard any timestamp value without the valid bit set */
+		if (!(raw_tstamp & ICE_PTP_TS_VALID))
+			drop_ts = true;
+
 skip_ts_read:
 		spin_lock(&tx->lock);
-		if (raw_tstamp)
+		if (tx->verify_cached && raw_tstamp)
 			tx->tstamps[idx].cached_tstamp = raw_tstamp;
 		clear_bit(idx, tx->in_use);
 		skb = tx->tstamps[idx].skb;
@@ -836,6 +864,7 @@ ice_ptp_init_tx_e822(struct ice_pf *pf, struct ice_ptp_tx *tx, u8 port)
 	tx->block = port / ICE_PORTS_PER_QUAD;
 	tx->offset = (port % ICE_PORTS_PER_QUAD) * INDEX_PER_PORT_E822;
 	tx->len = INDEX_PER_PORT_E822;
+	tx->verify_cached = 0;
 
 	return ice_ptp_alloc_tx_tracker(tx);
 }
@@ -854,6 +883,11 @@ ice_ptp_init_tx_e810(struct ice_pf *pf, struct ice_ptp_tx *tx)
 	tx->block = pf->hw.port_info->lport;
 	tx->offset = 0;
 	tx->len = INDEX_PER_PORT_E810;
+	/* The E810 PHY does not provide a timestamp ready bitmap. Instead,
+	 * verify new timestamps against cached copy of the last read
+	 * timestamp.
+	 */
+	tx->verify_cached = 1;
 
 	return ice_ptp_alloc_tx_tracker(tx);
 }