net: dsa: check out-of-range ageing time value

If a DSA switch driver cannot program an ageing time value due to it
being out-of-range, switchdev will raise a stack trace before failing.

To fix this, add ageing_time_min and ageing_time_max members to the
dsa_switch in order for the switch drivers to optionally specify their
supported ageing time limits.

The DSA core will now check for provided ageing time limits and return
-ERANGE from the switchdev prepare phase if the value is out-of-range.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -233,6 +233,10 @@ struct dsa_switch {
 	u32			phys_mii_mask;
 	struct mii_bus		*slave_mii_bus;
 
+	/* Ageing Time limits in msecs */
+	unsigned int ageing_time_min;
+	unsigned int ageing_time_max;
+
 	/* Dynamically allocated ports, keep last */
 	size_t num_ports;
 	struct dsa_port ports[];

net/dsa/slave.c

@@ -443,9 +443,13 @@ static int dsa_slave_ageing_time(struct net_device *dev,
 	unsigned long ageing_jiffies = clock_t_to_jiffies(attr->u.ageing_time);
 	unsigned int ageing_time = jiffies_to_msecs(ageing_jiffies);
 
-	/* bridge skips -EOPNOTSUPP, so skip the prepare phase */
-	if (switchdev_trans_ph_prepare(trans))
+	if (switchdev_trans_ph_prepare(trans)) {
+		if (ds->ageing_time_min && ageing_time < ds->ageing_time_min)
+			return -ERANGE;
+		if (ds->ageing_time_max && ageing_time > ds->ageing_time_max)
+			return -ERANGE;
 		return 0;
+	}
 
 	/* Keep the fastest ageing time in case of multiple bridges */
 	p->dp->ageing_time = ageing_time;