[PATCH v5 7/8] can-dev: introduce helpers to access Classical CAN DLC values

[Oliver Hartkopp <socketcan@hartkopp.net>]

can_get_len8_dlc: get value to fill len8_dlc at frame reception time
can_get_cc_dlc: get DLC value to be written into CAN controller

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 include/linux/can/dev.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index e767a96ae075..f25558609d09 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -168,10 +168,29 @@ 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 handle len8_dlc value for Classical CAN raw DLC access */
+static inline u8 can_check_len8_dlc(u32 ctrlmode, u8 len, u8 dlc, u8 ret)
+{
+	/* return value for len8_dlc only if all conditions apply */
+	if ((ctrlmode & CAN_CTRLMODE_CC_LEN8_DLC) &&
+	    (len == CAN_MAX_DLEN) &&
+	    (dlc > CAN_MAX_DLEN && dlc <= CAN_MAX_RAW_DLC))
+		ret = dlc;
+
+	/* no valid len8_dlc value -> return provided default value */
+	return ret;
+}
+
+/* get value to fill len8_dlc in struct can_frame at frame reception time */
+#define can_get_len8_dlc(cm, len, dlc) can_check_len8_dlc(cm, len, dlc, 0)
+
+/* get DLC value to be written into Classical CAN controller at tx time */
+#define can_get_cc_dlc(cm, len, dlc) can_check_len8_dlc(cm, len, dlc, len)
+
 /* 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