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[ Upstream commit 9fde4c557f78ee2f3626e92b4089ce9d54a2573a ]
The Stuff Bit Count is always coded on 4 bits [1]. Update the Stuff
Bit Count size accordingly.
In addition, the CRC fields of CAN FD Frames contain stuff bits at
fixed positions called fixed stuff bits [2]. The CRC field starts with
a fixed stuff bit and then has another fixed stuff bit after each
fourth bit [2], which allows us to derive this formula:
FSB count = 1 + round_down(len(CRC field)/4)
The length of the CRC field is [1]:
len(CRC field) = len(Stuff Bit Count) + len(CRC)
= 4 + len(CRC)
with len(CRC) either 17 or 21 bits depending of the payload length.
In conclusion, for CRC17:
FSB count = 1 + round_down((4 + 17)/4)
= 6
and for CRC 21:
FSB count = 1 + round_down((4 + 21)/4)
= 7
Add a Fixed Stuff bits (FSB) field with above values and update
CANFD_FRAME_OVERHEAD_SFF and CANFD_FRAME_OVERHEAD_EFF accordingly.
[1] ISO 11898-1:2015 section 10.4.2.6 "CRC field":
The CRC field shall contain the CRC sequence followed by a recessive
CRC delimiter. For FD Frames, the CRC field shall also contain the
stuff count.
Stuff count
If FD Frames, the stuff count shall be at the beginning of the CRC
field. It shall consist of the stuff bit count modulo 8 in a 3-bit
gray code followed by a parity bit [...]
[2] ISO 11898-1:2015 paragraph 10.5 "Frame coding":
In the CRC field of FD Frames, the stuff bits shall be inserted at
fixed positions; they are called fixed stuff bits. There shall be a
fixed stuff bit before the first bit of the stuff count, even if the
last bits of the preceding field are a sequence of five consecutive
bits of identical value, there shall be only the fixed stuff bit,
there shall not be two consecutive stuff bits. A further fixed stuff
bit shall be inserted after each fourth bit of the CRC field [...]
Fixes: 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce function to get data length of frame in data link layer")
Suggested-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Thomas Kopp <Thomas.Kopp@microchip.com>
Link: https://lore.kernel.org/all/20230611025728.450837-2-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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of frame in data link layer
This patch adds the function can_skb_get_frame_len() which returns the length
of a CAN frame on the data link layer, including Start-of-frame, Identifier,
various other bits, the actual data, the CRC, the End-of-frame, the Inter frame
spacing.
Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Co-developed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Co-developed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20210111141930.693847-11-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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The data field in CAN-FD frames have specifig frame length (0, 1, 2, 3, 4, 5,
6, 7, 8, 12, 16, 20, 24, 32, 48, 64). This function "rounds" up a given length
to the next valid CAN-FD frame length.
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20210111141930.693847-10-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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This patch moves all CAN frame length related code of the CAN device
infrastructure into a separate file.
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20210111141930.693847-5-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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