From ea7800565a128c1adafa1791ce80afd6016fe21c Mon Sep 17 00:00:00 2001 From: Oliver Hartkopp Date: Tue, 10 Nov 2020 11:18:45 +0100 Subject: [PATCH] can: add optional DLC element to Classical CAN frame structure ISO 11898-1 Chapter 8.4.2.3 defines a 4 bit data length code (DLC) table which maps the DLC to the payload length of the CAN frame in bytes: DLC -> payload length 0 .. 8 -> 0 .. 8 9 .. 15 -> 8 Although the DLC values 8 .. 15 in Classical CAN always result in a payload length of 8 bytes these DLC values are transparently transmitted on the CAN bus. As the struct can_frame only provides a 'len' element (formerly 'can_dlc') which contains the plain payload length ( 0 .. 8 ) of the CAN frame, the raw DLC is not visible to the application programmer, e.g. for testing use-cases. To access the raw DLC values 9 .. 15 the len8_dlc element is introduced, which is only valid when the payload length 'len' is 8 and the DLC is greater than 8. The len8_dlc element is filled by the CAN interface driver and used for CAN frame creation by the CAN driver when the CAN_CTRLMODE_CC_LEN8_DLC flag is supported by the driver and enabled via netlink configuration interface. Reported-by: Vincent Mailhol Signed-off-by: Oliver Hartkopp Link: https://lore.kernel.org/r/20201110101852.1973-2-socketcan@hartkopp.net Signed-off-by: Marc Kleine-Budde --- include/uapi/linux/can.h | 38 ++++++++++++++++++++++++-------------- include/uapi/linux/can/netlink.h | 1 + 2 files changed, 25 insertions(+), 14 deletions(-) diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h index 6a6d2c7655ff..f75238ac6dce 100644 --- a/include/uapi/linux/can.h +++ b/include/uapi/linux/can.h @@ -84,6 +84,7 @@ typedef __u32 can_err_mask_t; /* CAN payload length and DLC definitions according to ISO 11898-1 */ #define CAN_MAX_DLC 8 +#define CAN_MAX_RAW_DLC 15 #define CAN_MAX_DLEN 8 /* CAN FD payload length and DLC definitions according to ISO 11898-7 */ @@ -91,23 +92,32 @@ typedef __u32 can_err_mask_t; #define CANFD_MAX_DLEN 64 /** - * struct can_frame - basic CAN frame structure - * @can_id: CAN ID of the frame and CAN_*_FLAG flags, see canid_t definition - * @can_dlc: frame payload length in byte (0 .. 8) aka data length code - * N.B. the DLC field from ISO 11898-1 Chapter 8.4.2.3 has a 1:1 - * mapping of the 'data length code' to the real payload length - * @__pad: padding - * @__res0: reserved / padding - * @__res1: reserved / padding - * @data: CAN frame payload (up to 8 byte) + * struct can_frame - Classical CAN frame structure (aka CAN 2.0B) + * @can_id: CAN ID of the frame and CAN_*_FLAG flags, see canid_t definition + * @len: CAN frame payload length in byte (0 .. 8) + * @can_dlc: deprecated name for CAN frame payload length in byte (0 .. 8) + * @__pad: padding + * @__res0: reserved / padding + * @len8_dlc: optional DLC value (9 .. 15) at 8 byte payload length + * len8_dlc contains values from 9 .. 15 when the payload length is + * 8 bytes but the DLC value (see ISO 11898-1) is greater then 8. + * CAN_CTRLMODE_CC_LEN8_DLC flag has to be enabled in CAN driver. + * @data: CAN frame payload (up to 8 byte) */ struct can_frame { canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */ - __u8 can_dlc; /* frame payload length in byte (0 .. CAN_MAX_DLEN) */ - __u8 __pad; /* padding */ - __u8 __res0; /* reserved / padding */ - __u8 __res1; /* reserved / padding */ - __u8 data[CAN_MAX_DLEN] __attribute__((aligned(8))); + union { + /* CAN frame payload length in byte (0 .. CAN_MAX_DLEN) + * was previously named can_dlc so we need to carry that + * name for legacy support + */ + __u8 len; + __u8 can_dlc; /* deprecated */ + }; + __u8 __pad; /* padding */ + __u8 __res0; /* reserved / padding */ + __u8 len8_dlc; /* optional DLC for 8 byte payload length (9 .. 15) */ + __u8 data[CAN_MAX_DLEN] __attribute__((aligned(8))); }; /* diff --git a/include/uapi/linux/can/netlink.h b/include/uapi/linux/can/netlink.h index 6f598b73839e..f730d443b918 100644 --- a/include/uapi/linux/can/netlink.h +++ b/include/uapi/linux/can/netlink.h @@ -100,6 +100,7 @@ struct can_ctrlmode { #define CAN_CTRLMODE_FD 0x20 /* CAN FD mode */ #define CAN_CTRLMODE_PRESUME_ACK 0x40 /* Ignore missing CAN ACKs */ #define CAN_CTRLMODE_FD_NON_ISO 0x80 /* CAN FD in non-ISO mode */ +#define CAN_CTRLMODE_CC_LEN8_DLC 0x100 /* Classic CAN DLC option */ /* * CAN device statistics -- 2.11.0