i2c: Retry automatically on arbitration loss

Some small changes in i2c core to retry i2c xfers until either the
maximum number of retries or the timeout is hit.

Signed-off-by: Clifford Wolf <[e-mail]>
Signed-off-by: Jean Delvare <[e-mail]>

drivers/i2c/i2c-core.c

···
  */
 int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 {
-	int ret;
+	unsigned long orig_jiffies;
+	int ret, try;
 
 	/* REVISIT the fault reporting model here is weak:
 	 *
···
 			mutex_lock_nested(&adap->bus_lock, adap->level);
 		}
 
-		ret = adap->algo->master_xfer(adap,msgs,num);
+		/* Retry automatically on arbitration loss */
+		orig_jiffies = jiffies;
+		for (ret = 0, try = 0; try <= adap->retries; try++) {
+			ret = adap->algo->master_xfer(adap, msgs, num);
+			if (ret != -EAGAIN)
+				break;
+			if (time_after(jiffies, orig_jiffies + adap->timeout))
+				break;
+		}
 		mutex_unlock(&adap->bus_lock);
 
 		return ret;
···
 		   char read_write, u8 command, int protocol,
 		   union i2c_smbus_data *data)
 {
+	unsigned long orig_jiffies;
+	int try;
 	s32 res;
 
 	flags &= I2C_M_TEN | I2C_CLIENT_PEC;
 
 	if (adapter->algo->smbus_xfer) {
 		mutex_lock(&adapter->bus_lock);
-		res = adapter->algo->smbus_xfer(adapter,addr,flags,read_write,
-						command, protocol, data);
+
+		/* Retry automatically on arbitration loss */
+		orig_jiffies = jiffies;
+		for (res = 0, try = 0; try <= adapter->retries; try++) {
+			res = adapter->algo->smbus_xfer(adapter, addr, flags,
+							read_write, command,
+							protocol, data);
+			if (res != -EAGAIN)
+				break;
+			if (time_after(jiffies,
+				       orig_jiffies + adapter->timeout))
+				break;
+		}
 		mutex_unlock(&adapter->bus_lock);
 	} else
 		res = i2c_smbus_xfer_emulated(adapter,addr,flags,read_write,