net: dsa: mv88e6xxx: wait for AVB Busy bit

The AVB is not an indirect table using an Update bit, but a unit using
a Busy bit. This means that we must ensure that this bit is cleared
before setting it and wait until it gets cleared again after writing
an operation. Reflect that.
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/global2_avb.c

@@ -11,6 +11,8 @@
  *	Brandon Streiff <brandon.streiff@ni.com>
  */
 
+#include <linux/bitfield.h>
+
 #include "global2.h"
 
 /* Offset 0x16: AVB Command Register
@@ -27,17 +29,33 @@
 /* mv88e6xxx_g2_avb_read -- Read one or multiple 16-bit words.
  * The hardware supports snapshotting up to four contiguous registers.
  */
+static int mv88e6xxx_g2_avb_wait(struct mv88e6xxx_chip *chip)
+{
+	int bit = __bf_shf(MV88E6352_G2_AVB_CMD_BUSY);
+
+	return mv88e6xxx_g2_wait_bit(chip, MV88E6352_G2_AVB_CMD, bit, 0);
+}
+
 static int mv88e6xxx_g2_avb_read(struct mv88e6xxx_chip *chip, u16 readop,
 				 u16 *data, int len)
 {
 	int err;
 	int i;
 
+	err = mv88e6xxx_g2_avb_wait(chip);
+	if (err)
+		return err;
+
 	/* Hardware can only snapshot four words. */
 	if (len > 4)
 		return -E2BIG;
 
-	err = mv88e6xxx_g2_update(chip, MV88E6352_G2_AVB_CMD, readop);
+	err = mv88e6xxx_g2_write(chip, MV88E6352_G2_AVB_CMD,
+				 MV88E6352_G2_AVB_CMD_BUSY | readop);
+	if (err)
+		return err;
+
+	err = mv88e6xxx_g2_avb_wait(chip);
 	if (err)
 		return err;
 
@@ -57,11 +75,18 @@ static int mv88e6xxx_g2_avb_write(struct mv88e6xxx_chip *chip, u16 writeop,
 {
 	int err;
 
+	err = mv88e6xxx_g2_avb_wait(chip);
+	if (err)
+		return err;
+
 	err = mv88e6xxx_g2_write(chip, MV88E6352_G2_AVB_DATA, data);
 	if (err)
 		return err;
 
-	return mv88e6xxx_g2_update(chip, MV88E6352_G2_AVB_CMD, writeop);
+	err = mv88e6xxx_g2_write(chip, MV88E6352_G2_AVB_CMD,
+				 MV88E6352_G2_AVB_CMD_BUSY | writeop);
+
+	return mv88e6xxx_g2_avb_wait(chip);
 }
 
 static int mv88e6352_g2_avb_port_ptp_read(struct mv88e6xxx_chip *chip,