[PATCH net v2 4/5] net: dsa: b53: reject conflicting mirror destinations

[Florian Fainelli <florian.fainelli@broadcom.com>]

The mirror capture control register selects one destination for all
ingress and egress mirror sources. Adding a rule for a different capture
port currently overwrites that field and silently redirects all existing
mirror rules.

Read the capture control before changing any source masks and reject a
different destination while mirroring is enabled. Return an extack which
describes the hardware limitation, and propagate a failed capture-control
read rather than making the decision from uninitialized data.

Clear the capture-port field when the final source is removed so a later
rule can select a new destination.

Fixes: ed3af5fd08eb ("net: dsa: b53: Add support for port mirroring")
Reviewed-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 drivers/net/dsa/b53/b53_common.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index c38e8c5838bd..378f47e7250c 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -2543,7 +2543,19 @@ int b53_mirror_add(struct dsa_switch *ds, int port,
 		   struct netlink_ext_ack *extack)
 {
 	struct b53_device *dev = ds->priv;
-	u16 reg, loc;
+	u16 reg, loc, cap_ctl;
+	int ret;
+
+	ret = b53_read16(dev, B53_MGMT_PAGE, B53_MIR_CAP_CTL, &cap_ctl);
+	if (ret)
+		return ret;
+
+	if ((cap_ctl & MIRROR_EN) &&
+	    (cap_ctl & CAP_PORT_MASK) != mirror->to_local_port) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Only one mirroring destination is supported");
+		return -EOPNOTSUPP;
+	}
 
 	if (ingress)
 		loc = B53_IG_MIR_CTL;
@@ -2554,11 +2566,10 @@ int b53_mirror_add(struct dsa_switch *ds, int port,
 	reg |= BIT(port);
 	b53_write16(dev, B53_MGMT_PAGE, loc, reg);
 
-	b53_read16(dev, B53_MGMT_PAGE, B53_MIR_CAP_CTL, &reg);
-	reg &= ~CAP_PORT_MASK;
-	reg |= mirror->to_local_port;
-	reg |= MIRROR_EN;
-	b53_write16(dev, B53_MGMT_PAGE, B53_MIR_CAP_CTL, reg);
+	cap_ctl &= ~CAP_PORT_MASK;
+	cap_ctl |= mirror->to_local_port;
+	cap_ctl |= MIRROR_EN;
+	b53_write16(dev, B53_MGMT_PAGE, B53_MIR_CAP_CTL, cap_ctl);
 
 	return 0;
 }
@@ -2595,10 +2606,8 @@ void b53_mirror_del(struct dsa_switch *ds, int port,
 
 	b53_read16(dev, B53_MGMT_PAGE, B53_MIR_CAP_CTL, &reg);
 	/* Both no longer have ports, let's disable mirroring */
-	if (loc_disable && other_loc_disable) {
-		reg &= ~MIRROR_EN;
-		reg &= ~mirror->to_local_port;
-	}
+	if (loc_disable && other_loc_disable)
+		reg &= ~(MIRROR_EN | CAP_PORT_MASK);
 	b53_write16(dev, B53_MGMT_PAGE, B53_MIR_CAP_CTL, reg);
 }
 EXPORT_SYMBOL(b53_mirror_del);
-- 
2.53.0