Input: atmel_mxt_ts - return errors from i2c layer

The i2c layer can report a variety of errors, including -ENXIO for an i2c
NAK.  Instead of treating them all as -EIO, pass the actual i2c layer
error up to the caller.

However, still report as -EIO the unlikely case that a transaction was
partially completed, and no error message was returned from i2c_*().
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Henrik Rydberg <rydberg@euromail.se>

drivers/input/touchscreen/atmel_mxt_ts.c

@@ -396,6 +396,7 @@ static int __mxt_read_reg(struct i2c_client *client,
 {
 	struct i2c_msg xfer[2];
 	u8 buf[2];
+	int ret;
 
 	buf[0] = reg & 0xff;
 	buf[1] = (reg >> 8) & 0xff;
@@ -412,12 +413,17 @@ static int __mxt_read_reg(struct i2c_client *client,
 	xfer[1].len = len;
 	xfer[1].buf = val;
 
-	if (i2c_transfer(client->adapter, xfer, 2) != 2) {
-		dev_err(&client->dev, "%s: i2c transfer failed\n", __func__);
-		return -EIO;
+	ret = i2c_transfer(client->adapter, xfer, 2);
+	if (ret == 2) {
+		ret = 0;
+	} else {
+		if (ret >= 0)
+			ret = -EIO;
+		dev_err(&client->dev, "%s: i2c transfer failed (%d)\n",
+			__func__, ret);
 	}
 
-	return 0;
+	return ret;
 }
 
 static int mxt_read_reg(struct i2c_client *client, u16 reg, u8 *val)
@@ -428,17 +434,23 @@ static int mxt_read_reg(struct i2c_client *client, u16 reg, u8 *val)
 static int mxt_write_reg(struct i2c_client *client, u16 reg, u8 val)
 {
 	u8 buf[3];
+	int ret;
 
 	buf[0] = reg & 0xff;
 	buf[1] = (reg >> 8) & 0xff;
 	buf[2] = val;
 
-	if (i2c_master_send(client, buf, 3) != 3) {
-		dev_err(&client->dev, "%s: i2c send failed\n", __func__);
-		return -EIO;
+	ret = i2c_master_send(client, buf, 3);
+	if (ret == 3) {
+		ret = 0;
+	} else {
+		if (ret >= 0)
+			ret = -EIO;
+		dev_err(&client->dev, "%s: i2c send failed (%d)\n",
+			__func__, ret);
 	}
 
-	return 0;
+	return ret;
 }
 
 static int mxt_read_object_table(struct i2c_client *client,