[PATCH 5.15 090/181] net: dsa: make dsa_master_ioctl() see through port_hwtstamp_get() shims

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Vladimir Oltean <vladimir.oltean@xxxxxxx>

[ Upstream commit ed1fe1bebe18884b11e5536b5ac42e3a48960835 ]

There are multi-generational drivers like mv88e6xxx which have code like
this:

int mv88e6xxx_port_hwtstamp_get(struct dsa_switch *ds, int port,
				struct ifreq *ifr)
{
	if (!chip->info->ptp_support)
		return -EOPNOTSUPP;

	...
}

DSA wants to deny PTP timestamping on the master if the switch supports
timestamping too. However it currently relies on the presence of the
port_hwtstamp_get() callback to determine PTP capability, and this
clearly does not work in that case (method is present but returns
-EOPNOTSUPP).

We should not deny PTP on the DSA master for those switches which truly
do not support hardware timestamping.

Create a dsa_port_supports_hwtstamp() method which actually probes for
support by calling port_hwtstamp_get() and seeing whether that returned
-EOPNOTSUPP or not.

Fixes: f685e609a301 ("net: dsa: Deny PTP on master if switch supports it")
Link: https://patchwork.kernel.org/project/netdevbpf/patch/20221110124345.3901389-1-festevam@xxxxxxxxx/
Reported-by: Fabio Estevam <festevam@xxxxxxxxx>
Reported-by: Steffen Bätz <steffen@xxxxxxxxxxxx>
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Tested-by: Fabio Estevam <festevam@xxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/dsa/dsa_priv.h |  1 +
 net/dsa/master.c   |  3 +--
 net/dsa/port.c     | 16 ++++++++++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index a5c9bc7b66c6..e91265434354 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -198,6 +198,7 @@ static inline struct net_device *dsa_master_find_slave(struct net_device *dev,
 }
 
 /* port.c */
+bool dsa_port_supports_hwtstamp(struct dsa_port *dp, struct ifreq *ifr);
 void dsa_port_set_tag_protocol(struct dsa_port *cpu_dp,
 			       const struct dsa_device_ops *tag_ops);
 int dsa_port_set_state(struct dsa_port *dp, u8 state, bool do_fast_age);
diff --git a/net/dsa/master.c b/net/dsa/master.c
index e8e19857621b..69ec510abe83 100644
--- a/net/dsa/master.c
+++ b/net/dsa/master.c
@@ -204,8 +204,7 @@ static int dsa_master_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 		 * switch in the tree that is PTP capable.
 		 */
 		list_for_each_entry(dp, &dst->ports, list)
-			if (dp->ds->ops->port_hwtstamp_get ||
-			    dp->ds->ops->port_hwtstamp_set)
+			if (dsa_port_supports_hwtstamp(dp, ifr))
 				return -EBUSY;
 		break;
 	}
diff --git a/net/dsa/port.c b/net/dsa/port.c
index a21015d6bd36..31e8a7a8c3e6 100644
--- a/net/dsa/port.c
+++ b/net/dsa/port.c
@@ -75,6 +75,22 @@ static bool dsa_port_can_configure_learning(struct dsa_port *dp)
 	return !err;
 }
 
+bool dsa_port_supports_hwtstamp(struct dsa_port *dp, struct ifreq *ifr)
+{
+	struct dsa_switch *ds = dp->ds;
+	int err;
+
+	if (!ds->ops->port_hwtstamp_get || !ds->ops->port_hwtstamp_set)
+		return false;
+
+	/* "See through" shim implementations of the "get" method.
+	 * This will clobber the ifreq structure, but we will either return an
+	 * error, or the master will overwrite it with proper values.
+	 */
+	err = ds->ops->port_hwtstamp_get(ds, dp->index, ifr);
+	return err != -EOPNOTSUPP;
+}
+
 int dsa_port_set_state(struct dsa_port *dp, u8 state, bool do_fast_age)
 {
 	struct dsa_switch *ds = dp->ds;
-- 
2.35.1