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

From: Thomas.Kopp
Date: Thu Jun 01 2023 - 07:26:36 EST

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In reply to: Vincent MAILHOL: "Re: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits"
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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
>
> ACK.
>
> > > + * 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
>
> ACK.
>
> > > + * @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.
>
> Look again at the opening and closing bracket of
> __can_bitstuffing_len(). These are already out :)
> I indented the parameters of __can_bitstuffing_length() to highlight
> what is in and out.
>
> Maybe adding some newlines would help readability? Something like that:
>
> #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) \
> > > +)
> > 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.
>
> Same as above, these are already out.
Whoops - my bad, re-reading these portions both old and new look ok to me. No need for extra newlines from my point of view, just better attention at the reader side to the indentation which is already there - that greatly helps 😉

>
> > > +
> > > +/**
> > > + * 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 😊
>
> ACK. I will remove it from 2/3 and add it to 3/3.
>
> > For the entire series you can add my reviewed-by.
>
> I will do so.
> Thanks for picking my typos!

Best Regards,
Thomas

Next message: Bao D. Nguyen: "[PATCH v1 1/1] ufs: mcq: Fix the sq_head_slot wrap around logic"
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In reply to: Vincent MAILHOL: "Re: [PATCH v3 3/3] can: length: refactor frame lengths definition to add size in bits"
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