netdev - [PATCH net 8/9] can: remove false statement about 1:1 mapping between DLC and length

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251012142836.285370-9-mkl@pengutronix.de>
Date: Sun, 12 Oct 2025 16:20:52 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	kuba@...nel.org,
	linux-can@...r.kernel.org,
	kernel@...gutronix.de,
	Vincent Mailhol <mailhol@...nel.org>,
	Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH net 8/9] can: remove false statement about 1:1 mapping between DLC and length

From: Vincent Mailhol <mailhol@...nel.org>

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@...nel.org>
Link: https://patch.msgid.link/20251012-can-fd-doc-v1-1-86cc7d130026@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 Documentation/networking/can.rst | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
index 7650c4b5be5f..ccd321d29a8a 100644
--- a/Documentation/networking/can.rst
+++ b/Documentation/networking/can.rst
@@ -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
-- 
2.51.0