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>

diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
index b48140b..b7f4d76 100644 (file)
--- 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 521fdbc..abc978b 100644 (file)
--- 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 <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
+ * 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) <= 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 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