dsa: mv88e6xxx: Timeout based on iterations, not time

The mv88e6xxx driver times out operations on the switch based on
looping until an elapsed wall clock time is reached. However, if
usleep_range() sleeps much longer than expected, it could timeout with
an error without actually checking to see if the devices has completed
the operation. So replace the elapsed time with a fixed upper bound on
the number of loops.

Testing on various switches has shown that switches takes either 0 or
1 iteration, so a maximum of 16 iterations is a safe limit.
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -309,9 +309,9 @@ static int mv88e6xxx_serdes_write(struct mv88e6xxx_chip *chip, int reg, u16 val)
 static int mv88e6xxx_wait(struct mv88e6xxx_chip *chip, int addr, int reg,
 			  u16 mask)
 {
-	unsigned long timeout = jiffies + HZ / 10;
+	int i;
 
-	while (time_before(jiffies, timeout)) {
+	for (i = 0; i < 16; i++) {
 		u16 val;
 		int err;
 
@@ -375,7 +375,7 @@ static int _mv88e6xxx_reg_write(struct mv88e6xxx_chip *chip, int addr,
 static int mv88e6xxx_ppu_disable(struct mv88e6xxx_chip *chip)
 {
 	int ret;
-	unsigned long timeout;
+	int i;
 
 	ret = _mv88e6xxx_reg_read(chip, REG_GLOBAL, GLOBAL_CONTROL);
 	if (ret < 0)
@@ -386,8 +386,7 @@ static int mv88e6xxx_ppu_disable(struct mv88e6xxx_chip *chip)
 	if (ret)
 		return ret;
 
-	timeout = jiffies + 1 * HZ;
-	while (time_before(jiffies, timeout)) {
+	for (i = 0; i < 16; i++) {
 		ret = _mv88e6xxx_reg_read(chip, REG_GLOBAL, GLOBAL_STATUS);
 		if (ret < 0)
 			return ret;
@@ -403,8 +402,7 @@ static int mv88e6xxx_ppu_disable(struct mv88e6xxx_chip *chip)
 
 static int mv88e6xxx_ppu_enable(struct mv88e6xxx_chip *chip)
 {
-	int ret, err;
-	unsigned long timeout;
+	int ret, err, i;
 
 	ret = _mv88e6xxx_reg_read(chip, REG_GLOBAL, GLOBAL_CONTROL);
 	if (ret < 0)
@@ -415,8 +413,7 @@ static int mv88e6xxx_ppu_enable(struct mv88e6xxx_chip *chip)
 	if (err)
 		return err;
 
-	timeout = jiffies + 1 * HZ;
-	while (time_before(jiffies, timeout)) {
+	for (i = 0; i < 16; i++) {
 		ret = _mv88e6xxx_reg_read(chip, REG_GLOBAL, GLOBAL_STATUS);
 		if (ret < 0)
 			return ret;