can: canxl: introduce CAN XL data structure

This patch adds defines for data structures and length information for
CAN XL (CAN with eXtended data Length) which can transfer up to 2048
byte inside a single frame.

Notable changes from CAN FD:

- the 11 bit arbitration field is now named 'priority' instead of 'can_id'
  (there are no 29 bit identifiers nor RTR frames anymore)
- the data length needs a uint16 value to cover up to 2048 byte
  (the length element position is different to struct can[fd]_frame)
- new fields (SDT, AF) and a SEC bit have been introduced
- the virtual CAN interface identifier is not part if the CAN XL frame
  struct as this VCID value is stored in struct skbuff (analog to vlan id)
Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20220912170725.120748-5-socketcan@hartkopp.netSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

include/uapi/linux/can.h

@@ -48,6 +48,7 @@
 
 #include <linux/types.h>
 #include <linux/socket.h>
+#include <linux/stddef.h> /* for offsetof */
 
 /* controller area network (CAN) kernel definitions */
 
@@ -60,6 +61,7 @@
 #define CAN_SFF_MASK 0x000007FFU /* standard frame format (SFF) */
 #define CAN_EFF_MASK 0x1FFFFFFFU /* extended frame format (EFF) */
 #define CAN_ERR_MASK 0x1FFFFFFFU /* omit EFF, RTR, ERR flags */
+#define CANXL_PRIO_MASK CAN_SFF_MASK /* 11 bit priority mask */
 
 /*
  * Controller Area Network Identifier structure
@@ -73,6 +75,7 @@ typedef __u32 canid_t;
 
 #define CAN_SFF_ID_BITS		11
 #define CAN_EFF_ID_BITS		29
+#define CANXL_PRIO_BITS		CAN_SFF_ID_BITS
 
 /*
  * Controller Area Network Error Message Frame Mask structure
@@ -91,6 +94,16 @@ typedef __u32 can_err_mask_t;
 #define CANFD_MAX_DLC 15
 #define CANFD_MAX_DLEN 64
 
+/*
+ * CAN XL payload length and DLC definitions according to ISO 11898-1
+ * CAN XL DLC ranges from 0 .. 2047 => data length from 1 .. 2048 byte
+ */
+#define CANXL_MIN_DLC 0
+#define CANXL_MAX_DLC 2047
+#define CANXL_MAX_DLC_MASK 0x07FF
+#define CANXL_MIN_DLEN 1
+#define CANXL_MAX_DLEN 2048
+
 /**
  * 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
@@ -166,8 +179,46 @@ struct canfd_frame {
 	__u8    data[CANFD_MAX_DLEN] __attribute__((aligned(8)));
 };
 
+/*
+ * defined bits for canxl_frame.flags
+ *
+ * The canxl_frame.flags element contains two bits CANXL_XLF and CANXL_SEC
+ * and shares the relative position of the struct can[fd]_frame.len element.
+ * The CANXL_XLF bit ALWAYS needs to be set to indicate a valid CAN XL frame.
+ * As a side effect setting this bit intentionally breaks the length checks
+ * for Classical CAN and CAN FD frames.
+ *
+ * Undefined bits in canxl_frame.flags are reserved and shall be set to zero.
+ */
+#define CANXL_XLF 0x80 /* mandatory CAN XL frame flag (must always be set!) */
+#define CANXL_SEC 0x01 /* Simple Extended Content (security/segmentation) */
+
+/**
+ * struct canxl_frame - CAN with e'X'tended frame 'L'ength frame structure
+ * @prio:  11 bit arbitration priority with zero'ed CAN_*_FLAG flags
+ * @flags: additional flags for CAN XL
+ * @sdt:   SDU (service data unit) type
+ * @len:   frame payload length in byte (CANXL_MIN_DLEN .. CANXL_MAX_DLEN)
+ * @af:    acceptance field
+ * @data:  CAN XL frame payload (CANXL_MIN_DLEN .. CANXL_MAX_DLEN byte)
+ *
+ * @prio shares the same position as @can_id from struct can[fd]_frame.
+ */
+struct canxl_frame {
+	canid_t prio;  /* 11 bit priority for arbitration (canid_t) */
+	__u8    flags; /* additional flags for CAN XL */
+	__u8    sdt;   /* SDU (service data unit) type */
+	__u16   len;   /* frame payload length in byte */
+	__u32   af;    /* acceptance field */
+	__u8    data[CANXL_MAX_DLEN];
+};
+
 #define CAN_MTU		(sizeof(struct can_frame))
 #define CANFD_MTU	(sizeof(struct canfd_frame))
+#define CANXL_MTU	(sizeof(struct canxl_frame))
+#define CANXL_HDR_SIZE	(offsetof(struct canxl_frame, data))
+#define CANXL_MIN_MTU	(CANXL_HDR_SIZE + 64)
+#define CANXL_MAX_MTU	CANXL_MTU
 
 /* particular protocols of the protocol family PF_CAN */
 #define CAN_RAW		1 /* RAW sockets */