can: move sanity check for bitrate and tq into can_get_bittiming

This patch moves a sanity check in order to have a second user for CAN FD.
Also simplify the return value generation in can_get_bittiming() as only
correct return values of can_[calc|fixup]_bittiming() lead to a return value of
zero.
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev.c

@@ -260,20 +260,23 @@ static int can_get_bittiming(struct net_device *dev, struct can_bittiming *bt)
 	int err;
 
 	/* Check if the CAN device has bit-timing parameters */
-	if (priv->bittiming_const) {
+	if (!priv->bittiming_const)
+		return 0;
 
-		/* Non-expert mode? Check if the bitrate has been pre-defined */
-		if (!bt->tq)
-			/* Determine bit-timing parameters */
-			err = can_calc_bittiming(dev, bt);
-		else
-			/* Check bit-timing params and calculate proper brp */
-			err = can_fixup_bittiming(dev, bt);
-		if (err)
-			return err;
-	}
+	/*
+	 * Depending on the given can_bittiming parameter structure the CAN
+	 * timing parameters are calculated based on the provided bitrate OR
+	 * alternatively the CAN timing parameters (tq, prop_seg, etc.) are
+	 * provided directly which are then checked and fixed up.
+	 */
+	if (!bt->tq && bt->bitrate)
+		err = can_calc_bittiming(dev, bt);
+	else if (bt->tq && !bt->bitrate)
+		err = can_fixup_bittiming(dev, bt);
+	else
+		err = -EINVAL;
 
-	return 0;
+	return err;
 }
 
 /*
@@ -667,8 +670,6 @@ static int can_changelink(struct net_device *dev,
 		if (dev->flags & IFF_UP)
 			return -EBUSY;
 		memcpy(&bt, nla_data(data[IFLA_CAN_BITTIMING]), sizeof(bt));
-		if ((!bt.bitrate && !bt.tq) || (bt.bitrate && bt.tq))
-			return -EINVAL;
 		err = can_get_bittiming(dev, &bt);
 		if (err)
 			return err;