Factorise the databittiming validation out of can_validate() and move
it in the new add can_validate_databittiming() function. Also move
can_validate()'s comment because it is specific to CAN FD. This is a
preparation patch for the introduction of CAN XL as this databittiming
validation will be reused later on.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
---
Changelog:

v1 -> v2:

  - Move can_validate()'s comment block to
    can_validate_databittiming(). Consequently, the next patch

      can: netlink: remove comment in can_validate()

    is removed.

  - Change WARN_ON(1) into return -EOPNOTSUPP to suppress a gcc
    warning.
    Link: https://lore.kernel.org/linux-can/202509050259.NjPdQyAD-lkp@intel.com/
---
 drivers/net/can/dev/netlink.c | 64 +++++++++++++++++++++++++++++--------------
 1 file changed, 44 insertions(+), 20 deletions(-)

diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index 25c08adee9ade22a5dabdd3dec1b5eb1ee16a78e..549a2247d847dd26c8cb8c76ecb609256f549eb2 100644
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -100,10 +100,13 @@ static int can_validate_tdc(struct nlattr *data_tdc,
 	return 0;
 }
 
-static int can_validate(struct nlattr *tb[], struct nlattr *data[],
-			struct netlink_ext_ack *extack)
+static int can_validate_databittiming(struct nlattr *data[],
+				      struct netlink_ext_ack *extack,
+				      int ifla_can_data_bittiming, u32 flags)
 {
-	bool is_can_fd = false;
+	struct nlattr *data_tdc;
+	u32 tdc_flags;
+	bool is_on;
 	int err;
 
 	/* Make sure that valid CAN FD configurations always consist of
@@ -113,35 +116,56 @@ static int can_validate(struct nlattr *tb[], struct nlattr *data[],
 	 * - TDC parameters are coherent (details in can_validate_tdc())
 	 */
 
+	if (ifla_can_data_bittiming == IFLA_CAN_DATA_BITTIMING) {
+		data_tdc = data[IFLA_CAN_TDC];
+		tdc_flags = flags & CAN_CTRLMODE_FD_TDC_MASK;
+		is_on = flags & CAN_CTRLMODE_FD;
+	} else {
+		return -EOPNOTSUPP; /* Place holder for CAN XL */
+	}
+
+	if (is_on) {
+		if (!data[IFLA_CAN_BITTIMING] || !data[ifla_can_data_bittiming])
+			return -EOPNOTSUPP;
+	}
+
+	if (data[ifla_can_data_bittiming] || data_tdc) {
+		if (!is_on)
+			return -EOPNOTSUPP;
+	}
+
+	err = can_validate_bittiming(data, extack, ifla_can_data_bittiming);
+	if (err)
+		return err;
+
+	err = can_validate_tdc(data_tdc, extack, tdc_flags);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static int can_validate(struct nlattr *tb[], struct nlattr *data[],
+			struct netlink_ext_ack *extack)
+{
+	u32 flags = 0;
+	int err;
+
 	if (!data)
 		return 0;
 
 	if (data[IFLA_CAN_CTRLMODE]) {
 		struct can_ctrlmode *cm = nla_data(data[IFLA_CAN_CTRLMODE]);
 
-		is_can_fd = cm->flags & cm->mask & CAN_CTRLMODE_FD;
-
-		err = can_validate_tdc(data[IFLA_CAN_TDC], extack,
-				       cm->flags & CAN_CTRLMODE_FD_TDC_MASK);
-		if (err)
-			return err;
+		flags = cm->flags & cm->mask;
 	}
 
 	err = can_validate_bittiming(data, extack, IFLA_CAN_BITTIMING);
 	if (err)
 		return err;
 
-	if (is_can_fd) {
-		if (!data[IFLA_CAN_BITTIMING] || !data[IFLA_CAN_DATA_BITTIMING])
-			return -EOPNOTSUPP;
-	}
-
-	if (data[IFLA_CAN_DATA_BITTIMING] || data[IFLA_CAN_TDC]) {
-		if (!is_can_fd)
-			return -EOPNOTSUPP;
-	}
-
-	err = can_validate_bittiming(data, extack, IFLA_CAN_DATA_BITTIMING);
+	err = can_validate_databittiming(data, extack,
+					 IFLA_CAN_DATA_BITTIMING, flags);
 	if (err)
 		return err;
 

-- 
2.49.1