On 10/23/20 10:30 PM, Oliver Hartkopp wrote: > 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 CC stands for Classic CAN? Is this the "official" name? For example there was a press release to harmonize the CAN transceiver nameing recently: https://can-cia.org/news/press-releases/view/harmonized-transceiver-naming/2020/7/16/ > supported by the driver and enabled via netlink configuration interface. > > Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx> > --- > include/uapi/linux/can.h | 36 ++++++++++++++++++++------------ > include/uapi/linux/can/netlink.h | 1 + > 2 files changed, 24 insertions(+), 13 deletions(-) > > diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h > index 6a6d2c7655ff..bcf28ae7f14c 100644 > --- a/include/uapi/linux/can.h > +++ b/include/uapi/linux/can.h > @@ -82,34 +82,44 @@ typedef __u32 canid_t; > */ > 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 */ > #define CANFD_MAX_DLC 15 > #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) > + * @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 */ > + }; There was an old compiler version, which struggled with C99 initialized unions within structs.....So this change would break existing source, but I think that old compilers are long gone (for good). > + __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))); > }; > > /* > * defined bits for canfd_frame.flags > * > 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 > @@ -98,10 +98,11 @@ struct can_ctrlmode { > #define CAN_CTRLMODE_ONE_SHOT 0x08 /* One-Shot mode */ > #define CAN_CTRLMODE_BERR_REPORTING 0x10 /* Bus-error reporting */ > #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 > */ > struct can_device_stats { > Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
Attachment:
signature.asc
Description: OpenPGP digital signature
