[PATCH v6 7/8] can-dev: introduce helpers to access Classical CAN DLC values

[Oliver Hartkopp <socketcan@hartkopp.net>]

can_get_cc_dlc: get the data length code for Classical CAN raw DLC access
can_get_cc_len: get len and len8_dlc value for Classical CAN raw DLC access

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 include/linux/can/dev.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index e767a96ae075..9a787f73399e 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -168,10 +168,38 @@ static inline bool can_is_canfd_skb(const struct sk_buff *skb)
 {
 	/* the CAN specific type of skb is identified by its data length */
 	return skb->len == CANFD_MTU;
 }
 
+/* helper to get the data length code (DLC) for Classical CAN raw DLC access */
+static inline u8 can_get_cc_dlc(const u32 ctrlmode, const struct can_frame *cf)
+{
+	/* return len8_dlc as dlc value only if all conditions apply */
+	if ((ctrlmode & CAN_CTRLMODE_CC_LEN8_DLC) &&
+	    (cf->len == CAN_MAX_DLEN) &&
+	    (cf->len8_dlc > CAN_MAX_DLEN && cf->len8_dlc <= CAN_MAX_RAW_DLC))
+		return cf->len8_dlc;
+
+	/* return the payload length as dlc value */
+	return cf->len;
+}
+
+/* helper to get len and len8_dlc value for Classical CAN raw DLC access */
+static inline u8 can_get_cc_len(const u32 ctrlmode, struct can_frame *cf,
+				u8 dlc)
+{
+	/* the caller already ensured that dlc is a value from 0 .. 15 */
+	if ((ctrlmode & CAN_CTRLMODE_CC_LEN8_DLC) && (dlc > CAN_MAX_DLEN))
+		cf->len8_dlc = dlc;
+
+	/* limit the payload length 'len' to CAN_MAX_DLEN */
+	if (dlc > CAN_MAX_DLEN)
+		return CAN_MAX_DLEN;
+
+	return dlc;
+}
+
 /* helper to define static CAN controller features at device creation time */
 static inline void can_set_static_ctrlmode(struct net_device *dev,
 					   u32 static_mode)
 {
 	struct can_priv *priv = netdev_priv(dev);
-- 
2.28.0