net: dsa: mv88e6xxx: Preserve priority when setting CPU port.

The 6390 family uses an extended register to set the port connected to
the CPU. The lower 5 bits indicate the port, the upper three bits are
the priority of the frames as they pass through the switch, what
egress queue they should use, etc. Since frames being set to the CPU
are typically management frames, BPDU, IGMP, ARP, etc set the priority
to 7, the reset default, and the highest.

Fixes: 33641994a676 ("net: dsa: mv88e6xxx: Monitor and Management tables")
Signed-off-by: Andrew Lunn <[e-mail]>
Tested-by: Chris Healy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/dsa/mv88e6xxx/global1.c

···
 {
 	u16 ptr = MV88E6390_G1_MONITOR_MGMT_CTL_PTR_CPU_DEST;
 
+	/* Use the default high priority for management frames sent to
+	 * the CPU.
+	 */
+	port |= MV88E6390_G1_MONITOR_MGMT_CTL_PTR_CPU_DEST_MGMTPRI;
+
 	return mv88e6390_g1_monitor_write(chip, ptr, port);
 }
 

drivers/net/dsa/mv88e6xxx/global1.h

···
 #define MV88E6390_G1_MONITOR_MGMT_CTL_PTR_INGRESS_DEST		0x2000
 #define MV88E6390_G1_MONITOR_MGMT_CTL_PTR_EGRESS_DEST		0x2100
 #define MV88E6390_G1_MONITOR_MGMT_CTL_PTR_CPU_DEST		0x3000
+#define MV88E6390_G1_MONITOR_MGMT_CTL_PTR_CPU_DEST_MGMTPRI	0x00e0
 #define MV88E6390_G1_MONITOR_MGMT_CTL_DATA_MASK			0x00ff
 
 /* Offset 0x1C: Global Control 2 */