[PATCH net-next v8 1/3] net: stmmac: dwmac-socfpga: complete cross-timestamp on ATSNS

[Zxyan Zhu <zxyan0222@gmail.com>]

The Agilex5 smtg_crosststamp() handler polls XGMAC_INT_STATUS for TSIS
to learn that the auxiliary snapshot is latched.  TSIS is a transient,
read-to-clear status bit, so the poll is racy in two ways: a stale TSIS
from an unrelated event satisfies it before the snapshot is latched,
leaving *device unwritten while the call reports success, and a
concurrent reader of XGMAC_TIMESTAMP_STATUS can clear it and make the
poll time out.

The FIFO level is also reported by the ATSNS count in
XGMAC_TIMESTAMP_STATUS, which reading the register does not disturb.
Poll ATSNS instead of TSIS, after waiting for the PTP_ACR_ATSFC FIFO
clear, so a stale ATSNS cannot satisfy the poll before the new snapshot
is latched.

Hold aux_ts_lock across the whole sequence so a concurrent
PTP_CLK_REQ_EXTTS request cannot flush the FIFO between the poll and
the drain loop.

Fixes: fd8c4f645496 ("net: stmmac: socfpga: Add hardware supported cross-timestamp")
Signed-off-by: Zxyan Zhu <zxyan0222@gmail.com>
---
 .../ethernet/stmicro/stmmac/dwmac-socfpga.c   | 29 ++++++++++++++-----
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c
index 6d4bc1fe8f75..ee79b74bf21b 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c
@@ -337,8 +337,18 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 	acr_value = readl(ptpaddr + PTP_ACR);
 	acr_value |= PTP_ACR_ATSFC;
 	writel(acr_value, ptpaddr + PTP_ACR);
-	/* Release the mutex */
-	mutex_unlock(&priv->aux_ts_lock);
+
+	/* Wait for the FIFO clear, so the poll only sees snapshots from
+	 * this trigger.
+	 */
+	ret = readl_poll_timeout(ptpaddr + PTP_ACR, acr_value,
+				 !(acr_value & PTP_ACR_ATSFC), 10, 10000);
+	if (ret) {
+		mutex_unlock(&priv->aux_ts_lock);
+		netdev_err(priv->dev, "%s: Failed to clear snapshot FIFO\n",
+			   __func__);
+		return ret;
+	}
 
 	/* Trigger Internal snapshot signal. Create a rising edge by just toggle
 	 * the GPO0 to low and back to high.
@@ -349,10 +359,14 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 	gpio_value |= XGMAC_GPIO_GPO0;
 	writel(gpio_value, ioaddr + XGMAC_GPIO_STATUS);
 
-	/* Poll for time sync operation done */
-	ret = readl_poll_timeout(priv->ioaddr + XGMAC_INT_STATUS, v,
-				 (v & XGMAC_INT_TSIS), 100, 10000);
+	/* Poll ATSNS instead of the transient TSIS: the ATSNS count is
+	 * the FIFO level and is not cleared by reading the register.
+	 */
+	ret = readl_poll_timeout(ioaddr + XGMAC_TIMESTAMP_STATUS, v,
+				 FIELD_GET(XGMAC_TIMESTAMP_ATSNS_MASK, v),
+				 100, 10000);
 	if (ret) {
+		mutex_unlock(&priv->aux_ts_lock);
 		netdev_err(priv->dev, "%s: Wait for time sync operation timeout\n",
 			   __func__);
 		return ret;
@@ -364,8 +378,7 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 		.use_nsecs = false,
 	};
 
-	num_snapshot = FIELD_GET(XGMAC_TIMESTAMP_ATSNS_MASK,
-				 readl(ioaddr + XGMAC_TIMESTAMP_STATUS));
+	num_snapshot = FIELD_GET(XGMAC_TIMESTAMP_ATSNS_MASK, v);
 
 	/* Repeat until the timestamps are from the FIFO last segment */
 	for (i = 0; i < num_snapshot; i++) {
@@ -375,6 +388,8 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 		read_unlock_irqrestore(&priv->ptp_lock, flags);
 	}
 
+	mutex_unlock(&priv->aux_ts_lock);
+
 	get_smtgtime(priv->mii, SMTG_MDIO_ADDR, &smtg_time);
 	system->cycles = smtg_time;
 
-- 
2.34.1