Multiple tc matchall filters can use the same source port, direction and
capture destination, but the hardware represents that source with one
mask bit. Removing any one filter currently clears the bit even when
another filter still needs it, and can also disable mirroring globally.

Track references to each port's ingress and egress source bits. Program
a bit for the first reference and retain it until the last reference is
removed. Keep the two directions independent and ignore a deletion with
no matching reference to avoid underflow. The tc callbacks serialize this
accounting under RTNL.

Fixes: ed3af5fd08eb ("net: dsa: b53: Add support for port mirroring")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 drivers/net/dsa/b53/b53_common.c | 16 ++++++++++++++++
 drivers/net/dsa/b53/b53_priv.h   |  2 ++
 2 files changed, 18 insertions(+)

diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index 75033b28100e..b16167c9510b 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -2545,6 +2545,7 @@ int b53_mirror_add(struct dsa_switch *ds, int port,
 		   struct netlink_ext_ack *extack)
 {
 	struct b53_device *dev = ds->priv;
+	unsigned int *mirror_count = &dev->ports[port].mirror_count[ingress];
 	u16 reg, loc, cap_ctl;
 	int ret;
 
@@ -2559,6 +2560,11 @@ int b53_mirror_add(struct dsa_switch *ds, int port,
 		return -EOPNOTSUPP;
 	}
 
+	if (*mirror_count) {
+		(*mirror_count)++;
+		return 0;
+	}
+
 	if (ingress)
 		loc = B53_IG_MIR_CTL;
 	else
@@ -2573,6 +2579,8 @@ int b53_mirror_add(struct dsa_switch *ds, int port,
 	cap_ctl |= MIRROR_EN;
 	b53_write16(dev, B53_MGMT_PAGE, B53_MIR_CAP_CTL, cap_ctl);
 
+	(*mirror_count)++;
+
 	return 0;
 }
 EXPORT_SYMBOL(b53_mirror_add);
@@ -2581,9 +2589,17 @@ void b53_mirror_del(struct dsa_switch *ds, int port,
 		    struct dsa_mall_mirror_tc_entry *mirror)
 {
 	struct b53_device *dev = ds->priv;
+	unsigned int *mirror_count =
+		&dev->ports[port].mirror_count[mirror->ingress];
 	bool loc_disable = false, other_loc_disable = false;
 	u16 reg, loc;
 
+	if (!*mirror_count)
+		return;
+
+	if (--(*mirror_count))
+		return;
+
 	if (mirror->ingress)
 		loc = B53_IG_MIR_CTL;
 	else
diff --git a/drivers/net/dsa/b53/b53_priv.h b/drivers/net/dsa/b53/b53_priv.h
index 29cca7945df7..910c71618d0b 100644
--- a/drivers/net/dsa/b53/b53_priv.h
+++ b/drivers/net/dsa/b53/b53_priv.h
@@ -121,6 +121,8 @@ struct b53_pcs {
 struct b53_port {
 	u16		vlan_ctl_mask;
 	u16		pvid;
+	/* References to each egress/ingress mirror source mask bit. */
+	unsigned int	mirror_count[2];
 	struct ethtool_keee eee;
 };
 
-- 
2.53.0