[PATCH net-next v4 2/2] net: stmmac: dwmac-socfpga: mask XGMAC_TSIE during cross-timestamp

[Zxyan Zhu <zxyan0222@gmail.com>]

The Agilex5 smtg_crosststamp() handler arms an internal auxiliary
snapshot, toggles GPO0 and then polls XGMAC_INT_STATUS for TSIS in
process context to learn that the snapshot is ready.  Unlike the Intel
cross-timestamp path it does not set STMMAC_FLAG_INT_SNAPSHOT_EN, so it
relies on nothing else consuming TSIS.

Once XGMAC_TSIE is unmasked (done by a companion change that enables it
in XGMAC_INT_DEFAULT_EN), the DWXGMAC2 timestamp interrupt handler runs
from hardirq on every timestamp event and clears TSIS by reading
XGMAC_TIMESTAMP_STATUS.  That read can win the race against the poll
loop, which then times out and makes PTP_SYS_OFFSET_PRECISE fail with
"Wait for time sync operation timeout".

Mask XGMAC_TSIE around the snapshot trigger and FIFO read so the hardirq
handler cannot clear TSIS while smtg_crosststamp() owns it, and restore
it on every return path.

Tested-by: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade@altera.com>
Signed-off-by: Zxyan Zhu <zxyan0222@gmail.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c
index 1d7f0a57d288..a4d00bf81423 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c
@@ -310,6 +310,13 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 	if (priv->plat->flags & STMMAC_FLAG_EXT_SNAPSHOT_EN)
 		return -EBUSY;
 
+	/* The XGMAC timestamp interrupt handler clears TSIS by reading
+	 * XGMAC_TIMESTAMP_STATUS, which would race with the TSIS poll
+	 * below.  Mask XGMAC_TSIE for the duration of the cross-timestamp
+	 * so the handler does not run while we own the snapshot FIFO.
+	 */
+	stmmac_mac_irq_modify(priv, XGMAC_TSIE, 0);
+
 	mutex_lock(&priv->aux_ts_lock);
 	/* Enable Internal snapshot trigger */
 	acr_value = readl(ptpaddr + PTP_ACR);
@@ -329,6 +336,7 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 		break;
 	default:
 		mutex_unlock(&priv->aux_ts_lock);
+		stmmac_mac_irq_modify(priv, 0, XGMAC_TSIE);
 		return -EINVAL;
 	}
 	writel(acr_value, ptpaddr + PTP_ACR);
@@ -353,6 +361,7 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 	ret = readl_poll_timeout(priv->ioaddr + XGMAC_INT_STATUS, v,
 				 (v & XGMAC_INT_TSIS), 100, 10000);
 	if (ret) {
+		stmmac_mac_irq_modify(priv, 0, XGMAC_TSIE);
 		netdev_err(priv->dev, "%s: Wait for time sync operation timeout\n",
 			   __func__);
 		return ret;
@@ -375,6 +384,8 @@ static int smtg_crosststamp(ktime_t *device, struct system_counterval_t *system,
 		read_unlock_irqrestore(&priv->ptp_lock, flags);
 	}
 
+	stmmac_mac_irq_modify(priv, 0, XGMAC_TSIE);
+
 	get_smtgtime(priv->mii, SMTG_MDIO_ADDR, &smtg_time);
 	system->cycles = smtg_time;
 
-- 
2.34.1