"The (Re-)Synchronization Jump Width (SJW) defines how far a
resynchronization may move the Sample Point inside the limits defined
by the Phase Buffer Segments to compensate for edge phase errors." [1]
In other words, this means that the SJW parameter controls the
tolerance of the CAN controller to frequency errors compared to other
CAN controllers.
If the user space does not provide an SJW parameter, the kernel
chooses a default value of 1. This has proven to be a good default
value for classic CAN controllers, but no longer for modern CAN-FD
controllers.
In the past there were CAN controllers like the sja1000 with a rather
limited range of bit timing parameters. For the standard bit rates
this results in the following bit timing parameters:
| Bit timing parameters for sja1000 with 8.000000 MHz ref clock
| _----+--------------=> tseg1: 1 … 16
| / / _---------=> tseg2: 1 … 8
| | | / _-----=> sjw: 1 … 4
| | | | / _-=> brp: 1 … 64 (inc: 1)
| | | | | /
| nominal | | | | | real Bitrt nom real SampP
| Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error BTR0 BTR1
| 1000000 125 2 3 2 1 1 1000000 0.0% 75.0% 75.0% 0.0% 0x00 0x14
| 800000 125 3 4 2 1 1 800000 0.0% 80.0% 80.0% 0.0% 0x00 0x16
| 666666 125 4 4 3 1 1 666666 0.0% 80.0% 75.0% 6.2% 0x00 0x27
| 500000 125 6 7 2 1 1 500000 0.0% 87.5% 87.5% 0.0% 0x00 0x1c
| 250000 250 6 7 2 1 2 250000 0.0% 87.5% 87.5% 0.0% 0x01 0x1c
| 125000 500 6 7 2 1 4 125000 0.0% 87.5% 87.5% 0.0% 0x03 0x1c
| 100000 625 6 7 2 1 5 100000 0.0% 87.5% 87.5% 0.0% 0x04 0x1c
| 83333 750 6 7 2 1 6 83333 0.0% 87.5% 87.5% 0.0% 0x05 0x1c
| 50000 1250 6 7 2 1 10 50000 0.0% 87.5% 87.5% 0.0% 0x09 0x1c
| 33333 1875 6 7 2 1 15 33333 0.0% 87.5% 87.5% 0.0% 0x0e 0x1c
| 20000 3125 6 7 2 1 25 20000 0.0% 87.5% 87.5% 0.0% 0x18 0x1c
| 10000 6250 6 7 2 1 50 10000 0.0% 87.5% 87.5% 0.0% 0x31 0x1c
The attentive reader will notice that the SJW is 1 in most cases,
while the Seg2 phase is 2. Both values are given in TQ units, which in
turn is a duration in nanoseconds.
For example the 500 kbit/s configuration:
| nominal real Bitrt nom real SampP
| Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error BTR0 BTR1
| 500000 125 6 7 2 1 1 500000 0.0% 87.5% 87.5% 0.0% 0x00 0x1c
the TQ is 125ns, the Phase Seg2 is "2" (== 250ns), the SJW is "1" (==
125 ns).
Looking at a more modern CAN controller like a mcp2518fd, it has wider
bit timing registers.
| Bit timing parameters for mcp251xfd with 40.000000 MHz ref clock
| _----+--------------=> tseg1: 2 … 256
| / / _---------=> tseg2: 1 … 128
| | | / _-----=> sjw: 1 … 128
| | | | / _-=> brp: 1 … 256 (inc: 1)
| | | | | /
| nominal | | | | | real Bitrt nom real SampP
| Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error NBTCFG
| 500000 25 34 35 10 1 1 500000 0.0% 87.5% 87.5% 0.0% 0x00440900
The TQ is 25ns, the Phase Seg 2 is "10" (== 250ns), the SJW is "1" (==
25ns).
Since the kernel chooses a default SJW of 1 regardless of the TQ, this
leads to a much smaller SJW and thus much smaller tolerances to
frequency errors.
To maintain the same oscillator tolerances on controllers with wide
bit timing registers, select a default SJW value of Phase Seg2 / 2
unless Phase Seg 1 is less. This results in the following bit timing
parameters:
| Bit timing parameters for mcp251xfd with 40.000000 MHz ref clock
| _----+--------------=> tseg1: 2 … 256
| / / _---------=> tseg2: 1 … 128
| | | / _-----=> sjw: 1 … 128
| | | | / _-=> brp: 1 … 256 (inc: 1)
| | | | | /
| nominal | | | | | real Bitrt nom real SampP
| Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error NBTCFG
| 500000 25 34 35 10 5 1 500000 0.0% 87.5% 87.5% 0.0% 0x00440904
The TQ is 25ns, the Phase Seg 2 is "10" (== 250ns), the SJW is "5" (==
125ns). Which is the same as on the sja1000 controller.
[1] http://web.archive.org/http://www.oertel-halle.de/files/cia99paper.pdf
Link: https://lore.kernel.org/all/20230202110854.2318594-15-mkl@pengutronix.de
Cc: Mark Bath <mark@baggywrinkle.co.uk>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
If the user space has supplied an invalid SJW value (greater than the
maximum SJW value), report -EINVAL instead of -ERANGE, this better
matches the actual meaning of the error value.
Additionally report an error message via netlink to the user space.
Link: https://lore.kernel.org/all/20230202110854.2318594-13-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Factor out the functionality of assigning a SJW default value into
can_sjw_set_default() and the checking the SJW limits into
can_sjw_check().
This functions will be improved and called from a different function
in the following patches.
Link: https://lore.kernel.org/all/20230202110854.2318594-11-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This is a preparation patch.
In order to pass warning/error messages during netlink calls back to
user space, pass the extack struct down the callstack of
can_changelink(), the actual error messages will be added in the
following ptaches.
Link: https://lore.kernel.org/all/20230202110854.2318594-10-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Since commit 51c352bdbc ("netlink: add support for formatted extack
messages") formatted extack messages are supported to inform the user
space or warnings/errors during netlink calls.
Replace the netdev_err() by NL_SET_ERR_MSG_FMT() to better inform the
user about the problem. While there, use %u to print unsigned values
and improve error message a bit.
Link: https://lore.kernel.org/all/20230202110854.2318594-9-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Implement the function can_bittiming_const_valid() to check the
validity of the specified bit timing constant. Call this function from
register_candev() to check the bit timing constants during the
registration of the CAN interface.
Link: https://lore.kernel.org/all/20230202110854.2318594-6-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
The can_fixup_bittiming() function is used to validate the
user-supplied low-level bit timing parameters and calculate the
bitrate prescaler (brp) from the requested time quanta (tq) and the
CAN clock of the controller.
can_fixup_bittiming() selects the best matching integer bit rate
prescaler, which may result in a different time quantum than the value
specified by the user.
Calculate the resulting time quantum and assign it so that the user
sees the effective time quantum.
Link: https://lore.kernel.org/all/20230202110854.2318594-4-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Commit 1c47fa6b31 ("can: dev: add a helper function to calculate the
duration of one bit") made the constant CAN_SYNC_SEG available in a
header file.
The magic number 1 in can_fixup_bittiming() represents the width of
the sync segment, replace it by CAN_SYNC_SEG to make the code more
readable.
Link: https://lore.kernel.org/all/20230202110854.2318594-3-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Previously, the CAN channel ID was printed to the kernel log in decimal
upon connecting a new PEAK device. This behavior is inconsistent with
the hexadecimal format of the CAN channel ID sysfs attribute. This patch
updates the log message to output the id in hexadecimal.
Signed-off-by: Lukas Magel <lukas.magel@posteo.net>
Link: https://lore.kernel.org/all/20230116200932.157769-8-lukas.magel@posteo.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This patch exports the CAN channel ID as a sysfs attribute. The CAN
channel ID is a user-configurable u8/u32 identifier that can be set
individually for each CAN interface of a PEAK USB device.
Exporting the channel ID as a sysfs attribute allows users to easily read
the ID and to write udev rules that can match against the ID. This is
especially useful for PEAK USB devices that do not export a serial
number at SUB level.
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Lukas Magel <lukas.magel@posteo.net>
Link: https://lore.kernel.org/all/20230116200932.157769-7-lukas.magel@posteo.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This patch introduces 3 new functions implementing support for ethtool
access to the CAN channel ID of all USB CAN network interfaces managed by
the driver. With this patch, it is possible to read/write the CAN
channel ID from/to the EEPROM via the ethtool interface.
The CAN channel ID is a user-configurable device identifier that can be
set individually for each CAN interface of a PEAK USB device. Depending on
the device, the identifier has a length of 8 or 32 bit. The identifier
is stored in the non-volatile memory of the device.
The identifier of a CAN interface can be read/written as an 8 or 32 bit
byte string in native (little-endian) byte order, where the length depends
on the device type.
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Lukas Magel <lukas.magel@posteo.net>
Link: https://lore.kernel.org/all/20230116200932.157769-6-lukas.magel@posteo.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This patch adds callbacks that allow the user to set a new self-defined
CAN channel ID to all USB - CAN/CANFD interfaces of PEAK-System managed by
this driver, namely:
- PCAN-USB
- PCAN-USB FD
- PCAN-USB Pro FD
- PCAN-USB X6
- PCAN-Chip USB
- PCAN-USB Pro
The callback functions write the CAN channel ID to the non-volatile
memory of the devices.
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Lukas Magel <lukas.magel@posteo.net>
Link: https://lore.kernel.org/all/20230116200932.157769-4-lukas.magel@posteo.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
The so-called "device id" is a user-defined identifier value that can be
set individually for each CAN interface of a PEAK USB device.
Contrary to a static serial number, the value can be changed by the
user. With this ID, each CAN interface can be uniquely identified even if
the USB device does not export a proper serial number or the USB device
exports multiple CAN interfaces. In order to not confuse it with the
device ID used by the USB core and emphasize the link to the CAN
interface, the functions and variables for reading this user-defined
value are renamed to CAN channel ID.
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Lukas Magel <lukas.magel@posteo.net>
Link: https://lore.kernel.org/all/20230116200932.157769-2-lukas.magel@posteo.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Geert Uytterhoeven <geert+renesas@glider.be> says:
This patch series adds support for the CAN-FD interface on the Renesas
R-Car V4H (R8A779G0) SoC and support for CAN transceivers described as
PHYs to the R-Car CAN-FD driver. It includes several fixes for issues
(some minor) detected while adding the support and during testing.
More details can be found in the individual patches.
This has been tested on the Renesas White-Hawk development board using
cansend, candump, and canfdtest:
- Channel 0 uses an NXP TJR1443AT CAN transceiver, and works fine,
- Channels 1-7 use Microchip MCP2558FD-H/SN CAN transceivers (not
mounted for channels 4-7), which do not need explicit description.
While channel 1 works fine, channels 2-3 do not seem to work.
Hence despite the new fixes, the test results are similar to what Ulrich
Hecht reported for R-Car V3U on the Falcon development board before,
i.e. only channels 0 and 1 work (FTR, [2] does not help).
Whether this is a CAN-FD driver issue, a pin control issue, an IP core
issue, or an SoC integration issue is still to be seen...
[1] https://lore.kernel.org/all/f53a1bcca637ceeafb04ce3540a605532d3bc34a.1674036164.git.geert+renesas@glider.be
[2] commit e3e5bccc92446048 ("can: rcar_canfd:
rcar_canfd_configure_afl_rules(): Fix Rx FIFO entry setting") in
renesas-bsp/v5.10.147/rcar-5.2.0.rc3.
Link: https://lore.kernel.org/all/cover.1674499048.git.geert+renesas@glider.be
[mkl: applying patches 1...11 only]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
When adding support for R-Car V3U, the Global FD Configuration register
(CFDGFDCFG) and the Channel-specific CAN-FD Configuration Registers
(CFDCmFDCFG) were mixed up. Use the correct register, and apply the
selected CAN mode to all available channels.
Annotate the corresponding register bits, to make it clear they do
not exist on older variants.
Fixes: 45721c406d ("can: rcar_canfd: Add support for r8a779a0 SoC")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/all/388ddf312917eb9f6cc460a481f68402a876f9b5.1674499048.git.geert+renesas@glider.be
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
To send CAN traffic back to the incoming interface a special flag has to
be set. When creating a routing job for identical interfaces without this
flag the rule is created but has no effect.
This patch adds an error return value in the case that the CAN interfaces
are identical but the CGW_FLAGS_CAN_IIF_TX_OK flag was not set.
Reported-by: Jannik Hartung <jannik.hartung@tu-bs.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20230125055407.2053-1-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
