diff options
| author | Oliver Hartkopp <socketcan@hartkopp.net> | 2020-11-10 11:18:45 +0100 |
|---|---|---|
| committer | Marc Kleine-Budde <mkl@pengutronix.de> | 2020-11-20 09:43:29 +0100 |
| commit | ea7800565a128c1adafa1791ce80afd6016fe21c (patch) | |
| tree | 382831535a4110c793d1177432c27b8101dcecee /include/uapi/linux/can | |
| parent | b7d3c0e5930deb3c8f69d7572e17baf2f07c56db (diff) | |
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 <mailhol.vincent@wanadoo.fr>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/r/20201110101852.1973-2-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Diffstat (limited to 'include/uapi/linux/can')
| -rw-r--r-- | include/uapi/linux/can/netlink.h | 1 |
1 files changed, 1 insertions, 0 deletions
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 |