can: dev: move length related code into seperate file

This patch moves all CAN frame length related code of the CAN device
infrastructure into a separate file.

Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20210111141930.693847-5-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 48 insertions, 0 deletions

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
new file mode 100644
index 000000000000..156b9d17969a
--- /dev/null
+++ b/include/linux/can/length.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
+ */
+
+#ifndef _CAN_LENGTH_H
+#define _CAN_LENGTH_H
+
+/*
+ * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
+ * Classical CAN frame into a valid data length of max. 8 bytes.
+ *
+ * To be used in the CAN netdriver receive path to ensure conformance with
+ * ISO 11898-1 Chapter 8.4.2.3 (DLC field)
+ */
+#define can_cc_dlc2len(dlc)	(min_t(u8, (dlc), CAN_MAX_DLEN))
+
+/* 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);
+}
+
+/* get data length from raw data length code (DLC) */
+u8 can_fd_dlc2len(u8 dlc);
+
+/* map the sanitized data length to an appropriate data length code */
+u8 can_fd_len2dlc(u8 len);
+
+#endif /* !_CAN_LENGTH_H */