Commit 80a2fbce authored by Vincent Mailhol's avatar Vincent Mailhol Committed by Marc Kleine-Budde
Browse files

can: length: refactor frame lengths definition to add size in bits 



Introduce a method to calculate the exact size in bits of a CAN(-FD)
frame with or without dynamic bitstuffing.

These are all the possible combinations taken into account:

  - Classical CAN or CAN-FD
  - Standard or Extended frame format
  - CAN-FD CRC17 or CRC21
  - Include or not intermission

Instead of doing several individual macro definitions, declare the
can_frame_bits() function-like macro. To this extent, do a full
refactoring of the length definitions.

In addition add the can_frame_bytes(). This function-like macro
replaces the existing macro:

  - CAN_FRAME_OVERHEAD_SFF: can_frame_bytes(false, false, 0)
  - CAN_FRAME_OVERHEAD_EFF: can_frame_bytes(false, true, 0)
  - CANFD_FRAME_OVERHEAD_SFF: can_frame_bytes(true, false, 0)
  - CANFD_FRAME_OVERHEAD_EFF: can_frame_bytes(true, true, 0)

Function-like macros were chosen over inline functions because they
can be used to initialize const struct fields.

The different maximum frame lengths (maximum data length, including
intermission) are as follow:

   Frame type				bits	bytes
  -------------------------------------------------------
   Classic CAN SFF no bitstuffing	111	14
   Classic CAN EFF no bitstuffing	131	17
   Classic CAN SFF bitstuffing		135	17
   Classic CAN EFF bitstuffing		160	20
   CAN-FD SFF no bitstuffing		579	73
   CAN-FD EFF no bitstuffing		598	75
   CAN-FD SFF bitstuffing		712	89
   CAN-FD EFF bitstuffing		736	92

The macro CAN_FRAME_LEN_MAX and CANFD_FRAME_LEN_MAX are kept as an
alias to, respectively, can_frame_bytes(false, true, CAN_MAX_DLEN) and
can_frame_bytes(true, true, CANFD_MAX_DLEN).

In addition to the above:

 - Use ISO 11898-1:2015 definitions for the names of the CAN frame
   fields.
 - Include linux/bits.h for use of BITS_PER_BYTE.
 - Include linux/math.h for use of mult_frac() and
   DIV_ROUND_UP(). N.B: the use of DIV_ROUND_UP() is not new to this
   patch, but the include was previously omitted.
 - Add copyright 2023 for myself.

Suggested-by: default avatarThomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: default avatarVincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: default avatarThomas Kopp <Thomas.Kopp@microchip.com>
Link: https://lore.kernel.org/all/20230611025728.450837-4-mailhol.vincent@wanadoo.fr


Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent 10711b11

drivers/net/can/dev/length.c

+2 −13
Original line number Diff line number Diff line
@@ -78,18 +78,7 @@ unsigned int can_skb_get_frame_len(const struct sk_buff *skb) 
	else

		len = cf->len;



	if (can_is_canfd_skb(skb)) {

		if (cf->can_id & CAN_EFF_FLAG)

			len += CANFD_FRAME_OVERHEAD_EFF;

		else

			len += CANFD_FRAME_OVERHEAD_SFF;

	} else {

		if (cf->can_id & CAN_EFF_FLAG)

			len += CAN_FRAME_OVERHEAD_EFF;

		else

			len += CAN_FRAME_OVERHEAD_SFF;

	}



	return len;

	return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id & CAN_EFF_FLAG,

			       false, len);

}

EXPORT_SYMBOL_GPL(can_skb_get_frame_len);

include/linux/can/length.h

+214 −88
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

/* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>

 * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>

 * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@wanadoo.fr>

 * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>

 */



#ifndef _CAN_LENGTH_H

#define _CAN_LENGTH_H



#include <linux/bits.h>

#include <linux/can.h>

#include <linux/can/netlink.h>

#include <linux/math.h>



/*

 * Size of a Classical CAN Standard Frame

 * Size of a Classical CAN Standard Frame header in bits

 *

 * 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

 * Start Of Frame (SOF)				1

 * Arbitration field:

 *	base ID					11

 *	Remote Transmission Request (RTR)	1

 * Control field:

 *	IDentifier Extension bit (IDE)		1

 *	FD Format indicator (FDF)		1

 *	Data Length Code (DLC)			4

 *

 * rounded up and ignoring bitstuffing

 * including all fields preceding the data field, ignoring bitstuffing

 */

#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)

#define CAN_FRAME_HEADER_SFF_BITS 19



/*

 * Size of a Classical CAN Extended Frame

 * Size of a Classical CAN Extended Frame header in bits

 *

 * 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

 * Start Of Frame (SOF)				1

 * Arbitration field:

 *	base ID					11

 *	Substitute Remote Request (SRR)		1

 *	IDentifier Extension bit (IDE)		1

 *	ID extension				18

 *	Remote Transmission Request (RTR)	1

 * Control field:

 *	FD Format indicator (FDF)		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

 * including all fields preceding the data field, ignoring bitstuffing

 */

#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)

#define CAN_FRAME_HEADER_EFF_BITS 39



/*

 * Size of a CAN-FD Standard Frame

 * Size of a CAN-FD Standard Frame in bits

 *

 * Name of Field				Bits

 * ---------------------------------------------------------

 * Start-of-frame			1

 * Identifier				11

 * Start Of Frame (SOF)				1

 * Arbitration field:

 *	base ID					11

 *	Remote Request Substitution (RRS)	1

 * Identifier extension bit (IDE)	1

 * Flexible data rate format (FDF)	1

 * Reserved bit (r0)			1

 * Control field:

 *	IDentifier Extension bit (IDE)		1

 *	FD Format indicator (FDF)		1

 *	Reserved bit (res)			1

 *	Bit Rate Switch (BRS)			1

 *	Error Status Indicator (ESI)		1

 *	Data length code (DLC)			4

 * Data field				0...512

 * Stuff Bit Count (SBC)		4

 * CRC					0...16: 17 20...64:21

 * CRC delimiter (CD)			1

 * Fixed Stuff bits (FSB)		0...16: 6 20...64:7

 * ACK slot (AS)			1

 * ACK delimiter (AD)			1

 * End-of-frame (EOF)			7

 * Inter frame spacing			3

 *

 * assuming CRC21, rounded up and ignoring dynamic bitstuffing

 * including all fields preceding the data field, ignoring bitstuffing

 */

#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)

#define CANFD_FRAME_HEADER_SFF_BITS 22



/*

 * Size of a CAN-FD Extended Frame

 * Size of a CAN-FD Extended Frame in bits

 *

 * Name of Field				Bits

 * ---------------------------------------------------------

 * Start-of-frame			1

 * Identifier A				11

 * Substitute remote request (SRR)	1

 * Identifier extension bit (IDE)	1

 * Identifier B				18

 * Start Of Frame (SOF)				1

 * Arbitration field:

 *	base ID					11

 *	Substitute Remote Request (SRR)		1

 *	IDentifier Extension bit (IDE)		1

 *	ID extension				18

 *	Remote Request Substitution (RRS)	1

 * Flexible data rate format (FDF)	1

 * Reserved bit (r0)			1

 * Control field:

 *	FD Format indicator (FDF)		1

 *	Reserved bit (res)			1

 *	Bit Rate Switch (BRS)			1

 *	Error Status Indicator (ESI)		1

 *	Data length code (DLC)			4

 * Data field				0...512

 * Stuff Bit Count (SBC)		4

 * CRC					0...16: 17 20...64:21

 * CRC delimiter (CD)			1

 * Fixed Stuff bits (FSB)		0...16: 6 20...64:7

 * ACK slot (AS)			1

 * ACK delimiter (AD)			1

 * End-of-frame (EOF)			7

 * Inter frame spacing			3

 *

 * assuming CRC21, rounded up and ignoring dynamic bitstuffing

 * including all fields preceding the data field, ignoring bitstuffing

 */

#define CANFD_FRAME_HEADER_EFF_BITS 41



/*

 * Size of a CAN CRC Field in bits

 *

 * Name of Field			Bits

 * ---------------------------------------------------------

 * CRC sequence (CRC15)			15

 * CRC Delimiter			1

 *

 * ignoring bitstuffing

 */

#define CAN_FRAME_CRC_FIELD_BITS 16



/*

 * Size of a CAN-FD CRC17 Field in bits (length: 0..16)

 *

 * Name of Field			Bits

 * ---------------------------------------------------------

 * Stuff Count				4

 * CRC Sequence (CRC17)			17

 * CRC Delimiter			1

 * Fixed stuff bits			6

 */

#define CANFD_FRAME_CRC17_FIELD_BITS 28



/*

 * Size of a CAN-FD CRC21 Field in bits (length: 20..64)

 *

 * Name of Field			Bits

 * ---------------------------------------------------------

 * Stuff Count				4

 * CRC sequence (CRC21)			21

 * CRC Delimiter			1

 * Fixed stuff bits			7

 */

#define CANFD_FRAME_CRC21_FIELD_BITS 33



/*

 * Size of a CAN(-FD) Frame footer in bits

 *

 * Name of Field			Bits

 * ---------------------------------------------------------

 * ACK slot				1

 * ACK delimiter			1

 * End Of Frame (EOF)			7

 *

 * including all fields following the CRC field

 */

#define CAN_FRAME_FOOTER_BITS 9



/*

 * First part of the Inter Frame Space

 * (a.k.a. IMF - intermission field)

 */

#define CAN_INTERMISSION_BITS 3



/**

 * can_bitstuffing_len() - Calculate the maximum length with bitstuffing

 * @destuffed_len: length of a destuffed bit stream

 *

 * The worst bit stuffing case is a sequence in which dominant and

 * recessive bits alternate every four bits:

 *

 *   Destuffed: 1 1111  0000  1111  0000  1111

 *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o

 *

 * Nomenclature

 *

 *  - "0": dominant bit

 *  - "o": dominant stuff bit

 *  - "1": recessive bit

 *  - "i": recessive stuff bit

 *

 * Aside from the first bit, one stuff bit is added every four bits.

 *

 * Return: length of the stuffed bit stream in the worst case scenario.

 */

#define can_bitstuffing_len(destuffed_len)			\

	(destuffed_len + (destuffed_len - 1) / 4)



#define __can_bitstuffing_len(bitstuffing, destuffed_len)	\

	(bitstuffing ? can_bitstuffing_len(destuffed_len) :	\

		       destuffed_len)



#define __can_cc_frame_bits(is_eff, bitstuffing,		\

			    intermission, data_len)		\

(								\

	__can_bitstuffing_len(bitstuffing,			\

		(is_eff ? CAN_FRAME_HEADER_EFF_BITS :		\

			  CAN_FRAME_HEADER_SFF_BITS) +		\

		(data_len) * BITS_PER_BYTE +			\

		CAN_FRAME_CRC_FIELD_BITS) +			\

	CAN_FRAME_FOOTER_BITS +					\

	(intermission ? CAN_INTERMISSION_BITS : 0)		\

)



#define __can_fd_frame_bits(is_eff, bitstuffing,		\

			    intermission, data_len)		\

(								\

	__can_bitstuffing_len(bitstuffing,			\

		(is_eff ? CANFD_FRAME_HEADER_EFF_BITS :		\

			  CANFD_FRAME_HEADER_SFF_BITS) +	\

		(data_len) * BITS_PER_BYTE) +			\

	((data_len) <= 16 ?					\

		CANFD_FRAME_CRC17_FIELD_BITS :			\

		CANFD_FRAME_CRC21_FIELD_BITS) +			\

	CAN_FRAME_FOOTER_BITS +					\

	(intermission ? CAN_INTERMISSION_BITS : 0)		\

)



/**

 * can_frame_bits() - Calculate the number of bits on the wire in a

 *	CAN frame

 * @is_fd: true: CAN-FD frame; false: Classical CAN frame.

 * @is_eff: true: Extended frame; false: Standard frame.

 * @bitstuffing: true: calculate the bitstuffing worst case; false:

 *	calculate the bitstuffing best case (no dynamic

 *	bitstuffing). CAN-FD's fixed stuff bits are always included.

 * @intermission: if and only if true, include the inter frame space

 *	assuming no bus idle (i.e. only the intermission). Strictly

 *	speaking, the inter frame space is not part of the

 *	frame. However, it is needed when calculating the delay

 *	between the Start Of Frame of two consecutive frames.

 * @data_len: length of the data field in bytes. Correspond to

 *	can(fd)_frame->len. Should be zero for remote frames. No

 *	sanitization is done on @data_len and it shall have no side

 *	effects.

 *

 * Return: the numbers of bits on the wire of a CAN frame.

 */

#define can_frame_bits(is_fd, is_eff, bitstuffing,		\

		       intermission, data_len)			\

(								\

	is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,	\

				    intermission, data_len) :	\

		__can_cc_frame_bits(is_eff, bitstuffing,	\

				    intermission, data_len)	\

)



/*

 * Number of bytes in a CAN frame

 * (rounded up, including intermission)

 */

#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)

#define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)	\

	DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing,	\

				    true, data_len),		\

		     BITS_PER_BYTE)



/*

 * Maximum size of a Classical CAN frame

 * (rounded up and ignoring bitstuffing)

 * (rounded up, ignoring bitstuffing but including intermission)

 */

#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)

#define CAN_FRAME_LEN_MAX can_frame_bytes(false, true, false, CAN_MAX_DLEN)



/*

 * Maximum size of a CAN-FD frame

 * (rounded up and ignoring bitstuffing)

 * (rounded up, ignoring dynamic bitstuffing but including intermission)

 */

#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)

#define CANFD_FRAME_LEN_MAX can_frame_bytes(true, true, false, CANFD_MAX_DLEN)



/*

 * can_cc_dlc2len(value) - convert a given data length code (dlc) of a