can: netlink: add can_dtb_changelink()

Factorise the databittiming parsing out of can_changelink() and move
it in the new can_dtb_changelink() function. This is a preparation
patch for the introduction of CAN XL because the databittiming
changelink logic will be reused later on.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Link: https://patch.msgid.link/20250923-canxl-netlink-prep-v4-10-e720d28f66fe@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Author: vincent-mailhol

drivers/net/can/dev/netlink.c

@@ -221,12 +221,95 @@ static int can_tdc_changelink(struct data_bittiming_params *dbt_params,
 	return 0;
 }
 
+static int can_dbt_changelink(struct net_device *dev, struct nlattr *data[],
+			      bool fd, struct netlink_ext_ack *extack)
+{
+	struct nlattr *data_bittiming, *data_tdc;
+	struct can_priv *priv = netdev_priv(dev);
+	struct data_bittiming_params *dbt_params;
+	struct can_bittiming dbt;
+	bool need_tdc_calc = false;
+	u32 tdc_mask;
+	int err;
+
+	if (fd) {
+		data_bittiming = data[IFLA_CAN_DATA_BITTIMING];
+		data_tdc = data[IFLA_CAN_TDC];
+		dbt_params = &priv->fd;
+		tdc_mask = CAN_CTRLMODE_FD_TDC_MASK;
+	} else {
+		return -EOPNOTSUPP; /* Place holder for CAN XL */
+	}
+
+	if (!data_bittiming)
+		return 0;
+
+	/* Do not allow changing bittiming while running */
+	if (dev->flags & IFF_UP)
+		return -EBUSY;
+
+	/* Calculate bittiming parameters based on data_bittiming_const
+	 * if set, otherwise pass bitrate directly via do_set_bitrate().
+	 * Bail out if neither is given.
+	 */
+	if (!dbt_params->data_bittiming_const && !dbt_params->do_set_data_bittiming &&
+	    !dbt_params->data_bitrate_const)
+		return -EOPNOTSUPP;
+
+	memcpy(&dbt, nla_data(data_bittiming), sizeof(dbt));
+	err = can_get_bittiming(dev, &dbt, dbt_params->data_bittiming_const,
+				dbt_params->data_bitrate_const,
+				dbt_params->data_bitrate_const_cnt, extack);
+	if (err)
+		return err;
+
+	if (priv->bitrate_max && dbt.bitrate > priv->bitrate_max) {
+		NL_SET_ERR_MSG_FMT(extack,
+				   "CAN data bitrate %u bps surpasses transceiver capabilities of %u bps",
+				   dbt.bitrate, priv->bitrate_max);
+		return -EINVAL;
+	}
+
+	memset(&dbt_params->tdc, 0, sizeof(dbt_params->tdc));
+	if (data[IFLA_CAN_CTRLMODE]) {
+		struct can_ctrlmode *cm = nla_data(data[IFLA_CAN_CTRLMODE]);
+
+		need_tdc_calc = !(cm->mask & tdc_mask);
+	}
+	if (data_tdc) {
+		/* TDC parameters are provided: use them */
+		err = can_tdc_changelink(dbt_params, data_tdc, extack);
+		if (err) {
+			priv->ctrlmode &= ~tdc_mask;
+			return err;
+		}
+	} else if (need_tdc_calc) {
+		/* Neither of TDC parameters nor TDC flags are provided:
+		 * do calculation
+		 */
+		can_calc_tdco(&dbt_params->tdc, dbt_params->tdc_const, &dbt,
+			      &priv->ctrlmode, priv->ctrlmode_supported);
+	} /* else: both CAN_CTRLMODE_TDC_{AUTO,MANUAL} are explicitly
+	   * turned off. TDC is disabled: do nothing
+	   */
+
+	memcpy(&dbt_params->data_bittiming, &dbt, sizeof(dbt));
+
+	if (dbt_params->do_set_data_bittiming) {
+		/* Finally, set the bit-timing registers */
+		err = dbt_params->do_set_data_bittiming(dev);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 static int can_changelink(struct net_device *dev, struct nlattr *tb[],
 			  struct nlattr *data[],
 			  struct netlink_ext_ack *extack)
 {
 	struct can_priv *priv = netdev_priv(dev);
-	bool fd_tdc_flag_provided = false;
 	int err;
 
 	/* We need synchronization with dev->stop() */
@@ -273,8 +356,6 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
 		}
 
 		can_set_default_mtu(dev);
-
-		fd_tdc_flag_provided = cm->mask & CAN_CTRLMODE_FD_TDC_MASK;
 	}
 
 	if (data[IFLA_CAN_BITTIMING]) {
@@ -347,67 +428,10 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
 			return err;
 	}
 
-	if (data[IFLA_CAN_DATA_BITTIMING]) {
-		struct can_bittiming dbt;
-
-		/* Do not allow changing bittiming while running */
-		if (dev->flags & IFF_UP)
-			return -EBUSY;
-
-		/* Calculate bittiming parameters based on
-		 * data_bittiming_const if set, otherwise pass bitrate
-		 * directly via do_set_bitrate(). Bail out if neither
-		 * is given.
-		 */
-		if (!priv->fd.data_bittiming_const && !priv->fd.do_set_data_bittiming &&
-		    !priv->fd.data_bitrate_const)
-			return -EOPNOTSUPP;
-
-		memcpy(&dbt, nla_data(data[IFLA_CAN_DATA_BITTIMING]),
-		       sizeof(dbt));
-		err = can_get_bittiming(dev, &dbt,
-					priv->fd.data_bittiming_const,
-					priv->fd.data_bitrate_const,
-					priv->fd.data_bitrate_const_cnt,
-					extack);
-		if (err)
-			return err;
-
-		if (priv->bitrate_max && dbt.bitrate > priv->bitrate_max) {
-			NL_SET_ERR_MSG_FMT(extack,
-					   "CANFD data bitrate %u bps surpasses transceiver capabilities of %u bps",
-					   dbt.bitrate, priv->bitrate_max);
-			return -EINVAL;
-		}
-
-		memset(&priv->fd.tdc, 0, sizeof(priv->fd.tdc));
-		if (data[IFLA_CAN_TDC]) {
-			/* TDC parameters are provided: use them */
-			err = can_tdc_changelink(&priv->fd,
-						 data[IFLA_CAN_TDC], extack);
-			if (err) {
-				priv->ctrlmode &= ~CAN_CTRLMODE_FD_TDC_MASK;
-				return err;
-			}
-		} else if (!fd_tdc_flag_provided) {
-			/* Neither of TDC parameters nor TDC flags are
-			 * provided: do calculation
-			 */
-			can_calc_tdco(&priv->fd.tdc, priv->fd.tdc_const, &dbt,
-				      &priv->ctrlmode, priv->ctrlmode_supported);
-		} /* else: both CAN_CTRLMODE_TDC_{AUTO,MANUAL} are explicitly
-		   * turned off. TDC is disabled: do nothing
-		   */
-
-		memcpy(&priv->fd.data_bittiming, &dbt, sizeof(dbt));
-
-		if (priv->fd.do_set_data_bittiming) {
-			/* Finally, set the bit-timing registers */
-			err = priv->fd.do_set_data_bittiming(dev);
-			if (err)
-				return err;
-		}
-	}
+	/* CAN FD */
+	err = can_dbt_changelink(dev, data, true, extack);
+	if (err)
+		return err;
 
 	if (data[IFLA_CAN_TERMINATION]) {
 		const u16 termval = nla_get_u16(data[IFLA_CAN_TERMINATION]);