RE: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits

From: Thomas.Kopp
Date: Thu Jun 01 2023 - 06:32:07 EST

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> Introduce a method to calculate the exact size in bits of a CAN(-FD)
> frame with or without dynamic bitsuffing.
>
> 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)
>
> 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 name 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.
>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
> ---
> drivers/net/can/dev/length.c | 15 +-
> include/linux/can/length.h | 298 +++++++++++++++++++++++++----------
> 2 files changed, 213 insertions(+), 100 deletions(-)
>
> diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
> index b48140b1102e..b7f4d76dd444 100644
> --- a/drivers/net/can/dev/length.c
> +++ b/drivers/net/can/dev/length.c
> @@ -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);
> diff --git a/include/linux/can/length.h b/include/linux/can/length.h
> index 521fdbce2d69..ef6e78fa95b9 100644
> --- a/include/linux/can/length.h
> +++ b/include/linux/can/length.h
> @@ -1,132 +1,256 @@
> /* SPDX-License-Identifier: GPL-2.0 */
> /* Copyright (C) 2020 Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
> * Copyright (C) 2020 Marc Kleine-Budde <kernel@xxxxxxxxxxxxxx>
> - * Copyright (C) 2020 Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
> + * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
> */
>
> #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
> + * 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 indicatior (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 indicatior (FDF) 1
Nit: indicator, same above
> + * 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
> *
> - * 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 CANFD_FRAME_HEADER_EFF_BITS 41
>
> /*
> - * Size of a Classical CAN Extended Frame
> + * Size of a CAN CRC Field 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
> - * 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
> + * CRC sequence (CRC15) 15
> + * CRC Delimiter 1
> *
> - * rounded up and ignoring bitstuffing
> + * ignoring bitstuffing
> */
> -#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
> +#define CAN_FRAME_CRC_FIELD_BITS 16
>
> /*
> - * Size of a CAN-FD Standard Frame
> + * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
> *
> * Name of Field Bits
> * ---------------------------------------------------------
> - * Start-of-frame 1
> - * Identifier 11
> - * Remote Request Substitution (RRS) 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) 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
> - */
> -#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(67, 8)
> + * 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 Extended Frame
> + * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
> *
> * 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 Request Substitution (RRS) 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) 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
> - */
> -#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(86, 8)
> + * 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 bitsuffing
Nit: bitstuffing, same further down
> + * @bitstream_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 of 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) \
> +)
I think Footer and Intermission need to be pulled out of the parameter for __can_bitstuffing_length as these fields are never stuffed.
> +
> +#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) \
> +)
I think Footer and Intermission need to be pulled out of the parameter for __can_bitstuffing_length as these fields are never stuffed.
The CAN_FRAME_CRC_FIELD_BITS bits need to be pulled out of the can_bitstuffing_len. That portion of the Frame is not dynamically stuffed in FD frames.
> +
> +/**
> + * can_frame_bits() - Calculate the number of bits in on the wire in a
Nit: "in on the wire" -in
> + * CAN frame
> + * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
> + * @is_eff: true: Extended frame; false: Standard frame.
> + * @bitstuffing: true: calculate the bitsuffing worst case; false:
> + * calculate the bitsuffing best case (no dynamic
> + * bitsuffing). 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 gets added).
> + * @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.
> + *
> + * 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 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)
Ignoring dynamic bitstuffing
> */
> -#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
> --
> 2.39.3

I think your attribution of suggested-by for myself is mixed up for the patches 2/3 and 3/3 😊

For the entire series you can add my reviewed-by.

Thanks,
Thomas

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