can: drivers: introduce helpers to access Classical CAN DLC values

This patch adds the following helper to functions to access Classical CAN DLC
values.

can_get_cc_dlc(): get the data length code for Classical CAN raw DLC access
can_frame_set_cc_len(): set len and len8_dlc value for Classical CAN raw DLC access

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/r/20201110154913.1404582-2-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index e767a96ae0759b9432063b878c2a7d9f6d77cf0a..197a79535cc22628304de00e1338a2433f718396 100644 (file)
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -170,6 +170,31 @@ static inline bool can_is_canfd_skb(const struct sk_buff *skb)
        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 struct can_frame *cf, const u32 ctrlmode)
+{
+       /* 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 set len and len8_dlc value for Classical CAN raw DLC access */
+static inline void can_frame_set_cc_len(struct can_frame *cf, const u8 dlc,
+                                       const u32 ctrlmode)
+{
+       /* 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 */
+       cf->len = can_cc_dlc2len(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)