Commit c282993c authored Oct 13, 2025 by Vincent Mailhol Committed by Marc Kleine-Budde Oct 13, 2025

can: remove false statement about 1:1 mapping between DLC and length



The CAN-FD section of can.rst still states that there is a 1:1 mapping
between the Classical CAN DLC and its length. This is only true for
the DLC values up to 8. Beyond that point, the length remains at 8.

For reference, the mapping between the CAN DLC and the length is given
in below table [1]:

	 DLC value	CBFF and CEFF	FBFF and FEFF
	 [decimal]	    [byte]	    [byte]
	----------------------------------------------
		 0		 0		 0
		 1		 1		 1
		 2		 2		 2
		 3		 3		 3
		 4		 4		 4
		 5		 5		 5
		 6		 6		 6
		 7		 7		 7
		 8		 8		 8
		 9		 8		12
		10		 8		16
		11		 8		20
		12		 8		24
		13		 8		32
		14		 8		48
		15		 8		64

Remove the erroneous statement. Instead just state that the length of
a Classical CAN frame ranges from 0 to 8.

[1] ISO 11898-1:2024, Table 5 -- DLC: coding of the four LSB

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Link: https://patch.msgid.link/20251013-can-fd-doc-v2-1-5d53bdc8f2ad@kernel.org


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

parent 49836ff2

Documentation/networking/can.rst

+3 −4

Original line number	Diff line number	Diff line
		@@ -1398,10 +1398,9 @@ second bit timing has to be specified in order to enable the CAN FD bitrate.
		Additionally CAN FD capable CAN controllers support up to 64 bytes of
		payload. The representation of this length in can_frame.len and
		canfd_frame.len for userspace applications and inside the Linux network
		layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
		The data length code was a 1:1 mapping to the payload length in the Classical
		CAN frames anyway. The payload length to the bus-relevant DLC mapping is
		only performed inside the CAN drivers, preferably with the helper
		layer is a plain value from 0 .. 64 instead of the Classical CAN length
		which ranges from 0 to 8. The payload length to the bus-relevant DLC mapping
		is only performed inside the CAN drivers, preferably with the helper
		functions can_fd_dlc2len() and can_fd_len2dlc().

		The CAN netdevice driver capabilities can be distinguished by the network