net: dsa: b53: Do not clear existing mirrored port mask

[ Upstream commit c763ac43 ]

Clearing the existing bitmask of mirrored ports essentially prevents us
from capturing more than one port at any given time. This is clearly
wrong, do not clear the bitmask prior to setting up the new port.
Reported-by: Hubert Feurstein <h.feurstein@gmail.com>
Fixes: ed3af5fd ("net: dsa: b53: Add support for port mirroring")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/dsa/b53/b53_common.c

@@ -1584,7 +1584,6 @@ int b53_mirror_add(struct dsa_switch *ds, int port,
 		loc = B53_EG_MIR_CTL;
 
 	b53_read16(dev, B53_MGMT_PAGE, loc, &reg);
-	reg &= ~MIRROR_MASK;
 	reg |= BIT(port);
 	b53_write16(dev, B53_MGMT_PAGE, loc, reg);