[PATCH net-next] net: dsa: mv88e6xxx: read then write PVID

[Vivien Didelot]

The port register 0x07 contains more options than just the default VID,
even though they are not used yet. So prefer a read then write operation
over a direct write.

This also allows to keep track of the change through dynamic debug.

Signed-off-by: Vivien Didelot <vivien.dide...@savoirfairelinux.com>
---
 drivers/net/dsa/mv88e6xxx.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx.c b/drivers/net/dsa/mv88e6xxx.c
index 3a58a8a..1aee42d 100644
--- a/drivers/net/dsa/mv88e6xxx.c
+++ b/drivers/net/dsa/mv88e6xxx.c
@@ -1166,23 +1166,45 @@ int mv88e6xxx_port_stp_update(struct dsa_switch *ds, 
int port, u8 state)
        return 0;
 }
 
-static int _mv88e6xxx_port_pvid_get(struct dsa_switch *ds, int port, u16 *pvid)
+static int _mv88e6xxx_port_pvid(struct dsa_switch *ds, int port, u16 *new,
+                               u16 *old)
 {
+       u16 pvid;
        int ret;
 
        ret = _mv88e6xxx_reg_read(ds, REG_PORT(port), PORT_DEFAULT_VLAN);
        if (ret < 0)
                return ret;
 
-       *pvid = ret & PORT_DEFAULT_VLAN_MASK;
+       pvid = ret & PORT_DEFAULT_VLAN_MASK;
+
+       if (new) {
+               ret &= ~PORT_DEFAULT_VLAN_MASK;
+               ret |= *new & PORT_DEFAULT_VLAN_MASK;
+
+               ret = _mv88e6xxx_reg_write(ds, REG_PORT(port),
+                                          PORT_DEFAULT_VLAN, ret);
+               if (ret < 0)
+                       return ret;
+
+               netdev_dbg(ds->ports[port], "DefaultVID %d (was %d)\n", *new,
+                          pvid);
+       }
+
+       if (old)
+               *old = pvid;
 
        return 0;
 }
 
+static int _mv88e6xxx_port_pvid_get(struct dsa_switch *ds, int port, u16 *pvid)
+{
+       return _mv88e6xxx_port_pvid(ds, port, NULL, pvid);
+}
+
 static int _mv88e6xxx_port_pvid_set(struct dsa_switch *ds, int port, u16 pvid)
 {
-       return _mv88e6xxx_reg_write(ds, REG_PORT(port), PORT_DEFAULT_VLAN,
-                                  pvid & PORT_DEFAULT_VLAN_MASK);
+       return _mv88e6xxx_port_pvid(ds, port, &pvid, NULL);
 }
 
 static int _mv88e6xxx_vtu_wait(struct dsa_switch *ds)
-- 
2.7.2