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kernel/include/linux/can/length.h
Vincent Mailhol 80a2fbce45 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: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Link: https://lore.kernel.org/all/20230611025728.450837-4-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
2023-06-22 09:43:40 +02:00

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/* 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, 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 header in bits
*
* Name of Field Bits
* ---------------------------------------------------------
* 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
*
* including all fields preceding the data field, ignoring bitstuffing
*/
#define CAN_FRAME_HEADER_SFF_BITS 19
/*
* Size of a Classical CAN Extended Frame header in bits
*
* Name of Field Bits
* ---------------------------------------------------------
* 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
*
* including all fields preceding the data field, ignoring bitstuffing
*/
#define CAN_FRAME_HEADER_EFF_BITS 39
/*
* Size of a CAN-FD Standard Frame in bits
*
* Name of Field Bits
* ---------------------------------------------------------
* Start Of Frame (SOF) 1
* Arbitration field:
* base ID 11
* Remote Request Substitution (RRS) 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
*
* including all fields preceding the data field, ignoring bitstuffing
*/
#define CANFD_FRAME_HEADER_SFF_BITS 22
/*
* Size of a CAN-FD Extended Frame in bits
*
* Name of Field Bits
* ---------------------------------------------------------
* 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
* 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
*
* 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 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, ignoring bitstuffing but including intermission)
*/
#define CAN_FRAME_LEN_MAX can_frame_bytes(false, true, false, CAN_MAX_DLEN)
/*
* Maximum size of a CAN-FD frame
* (rounded up, ignoring dynamic bitstuffing but including intermission)
*/
#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
* 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);
/* 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)
{
return can_fd_dlc2len(can_fd_len2dlc(len));
}
#endif /* !_CAN_LENGTH_H */
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