can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer

This patch adds the function can_skb_get_frame_len() which returns the length
of a CAN frame on the data link layer, including Start-of-frame, Identifier,
various other bits, the actual data, the CRC, the End-of-frame, the Inter frame
spacing.

Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Co-developed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Co-developed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20210111141930.693847-11-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 120 insertions, 0 deletions

diff --git a/include/linux/can/length.h b/include/linux/can/length.h
index b2313b2a0b02..6995092b774e 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,11 +1,128 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
+ * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
  */
 
 #ifndef _CAN_LENGTH_H
 #define _CAN_LENGTH_H
 
 /*
+ * Size of a Classical CAN Standard Frame
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Start-of-frame			1
+ * Identifier				11
+ * Remote transmission request (RTR)	1
+ * Identifier extension bit (IDE)	1
+ * Reserved bit (r0)			1
+ * Data length code (DLC)		4
+ * Data field				0...64
+ * CRC					15
+ * CRC delimiter			1
+ * ACK slot				1
+ * ACK delimiter			1
+ * End-of-frame (EOF)			7
+ * Inter frame spacing			3
+ *
+ * rounded up and ignoring bitstuffing
+ */
+#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
+
+/*
+ * Size of a Classical CAN Extended Frame
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Start-of-frame			1
+ * Identifier A				11
+ * Substitute remote request (SRR)	1
+ * Identifier extension bit (IDE)	1
+ * Identifier B				18
+ * Remote transmission request (RTR)	1
+ * Reserved bits (r1, r0)		2
+ * Data length code (DLC)		4
+ * Data field				0...64
+ * CRC					15
+ * CRC delimiter			1
+ * ACK slot				1
+ * ACK delimiter			1
+ * End-of-frame (EOF)			7
+ * Inter frame spacing			3
+ *
+ * rounded up and ignoring bitstuffing
+ */
+#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
+
+/*
+ * Size of a CAN-FD Standard Frame
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Start-of-frame			1
+ * Identifier				11
+ * Reserved bit (r1)			1
+ * Identifier extension bit (IDE)	1
+ * Flexible data rate format (FDF)	1
+ * Reserved bit (r0)			1
+ * Bit Rate Switch (BRS)		1
+ * Error Status Indicator (ESI)		1
+ * Data length code (DLC)		4
+ * Data field				0...512
+ * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * CRC					0...16: 17 20...64:21
+ * CRC delimiter (CD)			1
+ * ACK slot (AS)			1
+ * ACK delimiter (AD)			1
+ * End-of-frame (EOF)			7
+ * Inter frame spacing			3
+ *
+ * assuming CRC21, rounded up and ignoring bitstuffing
+ */
+#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(61, 8)
+
+/*
+ * Size of a CAN-FD Extended Frame
+ *
+ * Name of Field			Bits
+ * ---------------------------------------------------------
+ * Start-of-frame			1
+ * Identifier A				11
+ * Substitute remote request (SRR)	1
+ * Identifier extension bit (IDE)	1
+ * Identifier B				18
+ * Reserved bit (r1)			1
+ * Flexible data rate format (FDF)	1
+ * Reserved bit (r0)			1
+ * Bit Rate Switch (BRS)		1
+ * Error Status Indicator (ESI)		1
+ * Data length code (DLC)		4
+ * Data field				0...512
+ * Stuff Bit Count (SBC)		0...16: 4 20...64:5
+ * CRC					0...16: 17 20...64:21
+ * CRC delimiter (CD)			1
+ * ACK slot (AS)			1
+ * ACK delimiter (AD)			1
+ * End-of-frame (EOF)			7
+ * Inter frame spacing			3
+ *
+ * assuming CRC21, rounded up and ignoring bitstuffing
+ */
+#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(80, 8)
+
+/*
+ * Maximum size of a Classical CAN frame
+ * (rounded up and ignoring bitstuffing)
+ */
+#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)
+
+/*
+ * Maximum size of a CAN-FD frame
+ * (rounded up and ignoring bitstuffing)
+ */
+#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)
+
+/*
  * 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.
  *
@@ -45,6 +162,9 @@ u8 can_fd_dlc2len(u8 dlc);
 /* map the sanitized data length to an appropriate data length code */
 u8 can_fd_len2dlc(u8 len);
 
+/* calculate the CAN Frame length in bytes of a given skb */
+unsigned int can_skb_get_frame_len(const struct sk_buff *skb);
+
 /* map the data length to an appropriate data link layer length */
 static inline u8 canfd_sanitize_len(u8 len)
 {