[PATCH v5 3/3] can: length: refactor frame lengths definition to add size in bits
From: HMS Incident Management
Date: Wed Jun 14 2023 - 16:40:38 EST
**We apologize for the delay in delivering this email, which was caused by a mail incident that occurred over the weekend on June 10th. This email was originally sent from vincent.mailhol@xxxxxxxxx on 06/11/2023 02:58:17
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
Signed-off-by: Vincent Mailhol
Reviewed-by: Thomas Kopp
---
drivers/net/can/dev/length.c | 15 +-
include/linux/can/length.h | 302 +++++++++++++++++++++++++----------
2 files changed, 216 insertions(+), 101 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..abc978b38f79 100644
--- a/include/linux/can/length.h
+++ b/include/linux/can/length.h
@@ -1,132 +1,258 @@
/* SPDX-License-Identifier: GPL-2.0 */
/* Copyright (C) 2020 Oliver Hartkopp
* Copyright (C) 2020 Marc Kleine-Budde
- * Copyright (C) 2020 Vincent Mailhol
+ * Copyright (C) 2020, 2023 Vincent Mailhol
*/
#ifndef _CAN_LENGTH_H
#define _CAN_LENGTH_H
+#include
#include
#include
+#include
/*
- * 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 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
*
- * rounded up and ignoring bitstuffing
+ * 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_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
+#define CAN_FRAME_HEADER_EFF_BITS 39
/*
- * Size of a Classical CAN Extended Frame
+ * 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
* ---------------------------------------------------------
- * 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
+ *
+ * ignoring bitstuffing
+ */
+#define CAN_FRAME_CRC_FIELD_BITS 16
+
+/*
+ * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
*
- * rounded up and ignoring bitstuffing
+ * Name of Field Bits
+ * ---------------------------------------------------------
+ * Stuff Count 4
+ * CRC Sequence (CRC17) 17
+ * CRC Delimiter 1
+ * Fixed stuff bits 6
*/
-#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
+#define CANFD_FRAME_CRC17_FIELD_BITS 28
/*
- * Size of a CAN-FD Standard Frame
+ * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
*
* 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 (CRC21) 21
+ * CRC Delimiter 1
+ * Fixed stuff bits 7
+ */
+#define CANFD_FRAME_CRC21_FIELD_BITS 33
/*
- * Size of a CAN-FD Extended Frame
+ * Size of a CAN(-FD) Frame footer 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 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)
+ * 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) 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 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
--
2.39.3