netdev - [PATCH net-next 1/2] net: stmmac: ptp: conditionally populate getcrosststamp() method

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Message-Id: <E1uto2d-00000001se4-0JSY@rmk-PC.armlinux.org.uk>
Date: Wed, 03 Sep 2025 15:00:51 +0100
From: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Richard Cochran <richardcochran@...il.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next 1/2] net: stmmac: ptp: conditionally populate
 getcrosststamp() method

drivers/char/ptp_chardev.c::ptp_clock_getcaps() uses the presence of
the getcrosststamp() method to indicate to userspace whether
rosststamping is supported or not. Therefore, we should not provide
this method unless it is functional. Only set this method pointer
in stmmac_ptp_register() if the platform glue provides the
necessary functionality.

This does not mean that it will be supported (see intel_crosststamp(),
which is the only implementation that may have support) but at least
we won't be suggesting that it is supported on many platforms where
there is no hope.

Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
index 3767ba495e78..8b4cf1a31633 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c
@@ -247,10 +247,7 @@ static int stmmac_get_syncdevicetime(ktime_t *device,
 {
 	struct stmmac_priv *priv = (struct stmmac_priv *)ctx;
 
-	if (priv->plat->crosststamp)
-		return priv->plat->crosststamp(device, system, ctx);
-	else
-		return -EOPNOTSUPP;
+	return priv->plat->crosststamp(device, system, ctx);
 }
 
 static int stmmac_getcrosststamp(struct ptp_clock_info *ptp,
@@ -278,7 +275,6 @@ const struct ptp_clock_info stmmac_ptp_clock_ops = {
 	.gettime64 = stmmac_get_time,
 	.settime64 = stmmac_set_time,
 	.enable = stmmac_enable,
-	.getcrosststamp = stmmac_getcrosststamp,
 };
 
 /* structure describing a PTP hardware clock */
@@ -296,7 +292,6 @@ const struct ptp_clock_info dwmac1000_ptp_clock_ops = {
 	.gettime64 = stmmac_get_time,
 	.settime64 = stmmac_set_time,
 	.enable = dwmac1000_ptp_enable,
-	.getcrosststamp = stmmac_getcrosststamp,
 };
 
 /**
@@ -332,6 +327,9 @@ void stmmac_ptp_register(struct stmmac_priv *priv)
 	if (priv->plat->ptp_max_adj)
 		priv->ptp_clock_ops.max_adj = priv->plat->ptp_max_adj;
 
+	if (priv->plat->crosststamp)
+		priv->ptp_clock_ops.getcrosststamp = stmmac_getcrosststamp;
+
 	rwlock_init(&priv->ptp_lock);
 	mutex_init(&priv->aux_ts_lock);
 
-- 
2.47.2