kernel.git/drivers/net/can/dev/bittiming.c, branch linux-6.1.y

can: bittiming: move bittiming calculation functions to calc_bittiming.c

2022-06-11T15:11:01Z

The canonical way to select or deselect an object during compilation is to use this pattern in the relevant Makefile: bar-$(CONFIG_FOO) := foo.o bittiming.c instead uses some #ifdef CONFIG_CAN_CALC_BITTIMG. Create a new file named calc_bittiming.c with all the functions which are conditionally compiled with CONFIG_CAN_CALC_BITTIMG and modify the Makefile according to above pattern. Link: https://lore.kernel.org/all/20220610143009.323579-4-mailhol.vincent@wanadoo.fr Signed-off-by: Vincent Mailhol Acked-by: Max Staudt Tested-by: Oliver Hartkopp Signed-off-by: Marc Kleine-Budde

can: bittiming: can_calc_bittiming(): prefer small bit rate pre-scalers over larger ones

2022-04-19T15:12:05Z

The CiA (CAN in Automation) lists in their Newsletter 1/2018 in the "Recommendation for the CAN FD bit-timing" [1] article several recommendations, one of them is: | Recommendation 3: Choose BRPA and BRPD as low as possible [1] https://can-newsletter.org/uploads/media/raw/f6a36d1461371a2f86ef0011a513712c.pdf With the current bit timing algorithm Srinivas Neeli noticed that on the Xilinx Versal ACAP board the CAN data bit timing parameters are not calculated optimally. For most bit rates, the bit rate prescaler (BRP) is != 1, although it's possible to configure the requested with a bit rate with a prescaler of 1: | Data Bit timing parameters for xilinx_can_fd2i with 79.999999 MHz ref clock (cmd-line) using algo 'v4.8' | nominal real Bitrt nom real SampP | Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error | 12000000 12 2 2 2 1 1 11428571 4.8% 75.0% 71.4% 4.8% | 10000000 25 1 1 1 1 2 9999999 0.0% 75.0% 75.0% 0.0% | 8000000 12 3 3 3 1 1 7999999 0.0% 75.0% 70.0% 6.7% | 5000000 50 1 1 1 1 4 4999999 0.0% 75.0% 75.0% 0.0% | 4000000 62 1 1 1 1 5 3999999 0.0% 75.0% 75.0% 0.0% | 2000000 125 1 1 1 1 10 1999999 0.0% 75.0% 75.0% 0.0% | 1000000 250 1 1 1 1 20 999999 0.0% 75.0% 75.0% 0.0% The bit timing parameter calculation algorithm iterates effectively from low to high BRP values. It selects a new best parameter set, if the sample point error of the current parameter set is equal or less to old best parameter set. If the given hardware constraints (clock rate and bit timing parameter constants) don't allow a sample point error of 0, the algorithm will first find a valid bit timing parameter set with a low BRP, but then will accept parameter sets with higher BRPs that have the same sample point error. This patch changes the algorithm to only accept a new parameter set, if the resulting sample point error is lower. This leads to the following data bit timing parameter for the Versal ACAP board: | Data Bit timing parameters for xilinx_can_fd2i with 79.999999 MHz ref clock (cmd-line) using algo 'can-next' | nominal real Bitrt nom real SampP | Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error | 12000000 12 2 2 2 1 1 11428571 4.8% 75.0% 71.4% 4.8% | 10000000 12 2 3 2 1 1 9999999 0.0% 75.0% 75.0% 0.0% | 8000000 12 3 3 3 1 1 7999999 0.0% 75.0% 70.0% 6.7% | 5000000 12 5 6 4 1 1 4999999 0.0% 75.0% 75.0% 0.0% | 4000000 12 7 7 5 1 1 3999999 0.0% 75.0% 75.0% 0.0% | 2000000 12 14 15 10 1 1 1999999 0.0% 75.0% 75.0% 0.0% | 1000000 25 14 15 10 1 2 999999 0.0% 75.0% 75.0% 0.0% Note: Due to HW constraints a data bit rate of 1 MBit/s with BRP = 1 is not possible. Link: https://lore.kernel.org/all/20220318144913.873614-1-mkl@pengutronix.de Link: https://lore.kernel.org/all/20220113203004.jf2rqj2pirhgx72i@pengutronix.de Cc: Srinivas Neeli Signed-off-by: Marc Kleine-Budde

can: bittiming: mark function arguments and local variables as const

2022-02-24T07:26:03Z

This patch marks the arguments of some functions as well as some local variables as constant. Link: https://lore.kernel.org/all/20220124215642.3474154-7-mkl@pengutronix.de Signed-off-by: Marc Kleine-Budde

can: bittiming: can_validate_bitrate(): simplify bit rate checking

2022-02-24T07:26:03Z

This patch simplifies the validation of the fixed bit rates. If a supported bit rate is found, directly return 0. If no valid bit rate is found return -EINVAL; Link: https://lore.kernel.org/all/20220124215642.3474154-6-mkl@pengutronix.de Signed-off-by: Marc Kleine-Budde

can: bittiming: replace CAN units with the generic ones from linux/units.h

2021-12-08T09:12:58Z

In [1], we introduced a set of units in linux/can/bittiming.h. Since then, generic SI prefixes were added to linux/units.h in [2]. Those new prefixes can perfectly replace CAN specific ones. This patch replaces all occurrences of the CAN units with their corresponding prefix (from linux/units) and the unit (as a comment) according to below table. CAN units SI metric prefix (from linux/units) + unit (as a comment) ------------------------------------------------------------------------ CAN_KBPS KILO /* BPS */ CAN_MBPS MEGA /* BPS */ CAM_MHZ MEGA /* Hz */ The definition are then removed from linux/can/bittiming.h [1] commit 1d7750760b70 ("can: bittiming: add CAN_KBPS, CAN_MBPS and CAN_MHZ macros") [2] commit 26471d4a6cf8 ("units: Add SI metric prefix definitions") Link: https://lore.kernel.org/all/20211124014536.782550-1-mailhol.vincent@wanadoo.fr Suggested-by: Jimmy Assarsson Suggested-by: Oliver Hartkopp Signed-off-by: Vincent Mailhol Signed-off-by: Marc Kleine-Budde

can: bittiming: change can_calc_tdco()'s prototype to not directly modify priv

2021-10-24T14:24:29Z

The function can_calc_tdco() directly retrieves can_priv from the net_device and directly modifies it. This is annoying for the upcoming patch. In drivers/net/can/dev/netlink.c:can_changelink(), the data bittiming are written to a temporary structure and memcpyed to can_priv only after everything succeeded. In the next patch, where we will introduce the netlink interface for TDC parameters, we will add a new TDC block which can potentially fail. For this reason, the data bittiming temporary structure has to be copied after that to-be-introduced TDC block. However, TDC also needs to access data bittiming information. We change the prototype so that the data bittiming structure is passed to can_calc_tdco() as an argument instead of retrieving it from priv. This way can_calc_tdco() can access the data bittiming before it gets memcpyed to priv. Link: https://lore.kernel.org/all/20210918095637.20108-4-mailhol.vincent@wanadoo.fr Signed-off-by: Vincent Mailhol Signed-off-by: Marc Kleine-Budde

can: bittiming: change unit of TDC parameters to clock periods

2021-10-24T14:24:28Z

In the current implementation, all Transmission Delay Compensation (TDC) parameters are expressed in time quantum. However, ISO 11898-1 actually specifies that these should be expressed in *minimum* time quantum. Furthermore, the minimum time quantum is specified to be "one node clock period long" (c.f. paragraph 11.3.1.1 "Bit time"). For sake of simplicity, we prefer to use the "clock period" term instead of "minimum time quantum" because we believe that it is more broadly understood. This patch fixes that discrepancy by updating the documentation and the formula for TDCO calculation. N.B. In can_calc_tdco(), the sample point (in time quantum) was calculated using a division, thus introducing a risk of rounding and truncation errors. On top of changing the unit to clock period, we also modified the formula to use only additions. Link: https://lore.kernel.org/all/20210918095637.20108-3-mailhol.vincent@wanadoo.fr Suggested-by: Stefan Mätje Signed-off-by: Vincent Mailhol Signed-off-by: Marc Kleine-Budde

can: bittiming: allow TDC{V,O} to be zero and add can_tdc_const::tdc{v,o,f}_min

2021-10-24T14:24:28Z

ISO 11898-1 specifies in section 11.3.3 "Transmitter delay compensation" that "the configuration range for [the] SSP position shall be at least 0 to 63 minimum time quanta." Because SSP = TDCV + TDCO, it means that we should allow both TDCV and TDCO to hold zero value in order to honor SSP's minimum possible value. However, current implementation assigned special meaning to TDCV and TDCO's zero values: * TDCV = 0 -> TDCV is automatically measured by the transceiver. * TDCO = 0 -> TDC is off. In order to allow for those values to really be zero and to maintain current features, we introduce two new flags: * CAN_CTRLMODE_TDC_AUTO indicates that the controller support automatic measurement of TDCV. * CAN_CTRLMODE_TDC_MANUAL indicates that the controller support manual configuration of TDCV. N.B.: current implementation failed to provide an option for the driver to indicate that only manual mode was supported. TDC is disabled if both CAN_CTRLMODE_TDC_AUTO and CAN_CTRLMODE_TDC_MANUAL flags are off, c.f. the helper function can_tdc_is_enabled() which is also introduced in this patch. Also, this patch adds three fields: tdcv_min, tdco_min and tdcf_min to struct can_tdc_const. While we are not convinced that those three fields could be anything else than zero, we can imagine that some controllers might specify a lower bound on these. Thus, those minimums are really added "just in case". Comments of struct can_tdc and can_tdc_const are updated accordingly. Finally, the changes are applied to the etas_es58x driver. Link: https://lore.kernel.org/all/20210918095637.20108-2-mailhol.vincent@wanadoo.fr Signed-off-by: Vincent Mailhol Signed-off-by: Marc Kleine-Budde

can: bittiming: can_fixup_bittiming(): change type of tseg1 and alltseg to unsigned int

2021-10-24T14:24:28Z

All timing calculation is done with unsigned integers, so change type of tseg1 and alltseg to unsigned int, too. Link: https://lore.kernel.org/all/20211013130653.1513627-1-mkl@pengutronix.de Link: https://github.com/linux-can/can-utils/pull/314 Reported-by: Gary Bisson Signed-off-by: Marc Kleine-Budde

can: bittiming: add CAN_KBPS, CAN_MBPS and CAN_MHZ macros

2021-03-30T09:14:45Z

Add three macro to simplify the readability of big bit timing numbers: - CAN_KBPS: kilobits per second (one thousand) - CAN_MBPS: megabits per second (one million) - CAN_MHZ: megahertz per second (one million) Example: u32 bitrate_max = 8 * CAN_MBPS; struct can_clock clock = {.freq = 80 * CAN_MHZ}; instead of: u32 bitrate_max = 8000000; struct can_clock clock = {.freq = 80000000}; Apply the new macro to driver/net/can/dev/bittiming.c. Link: https://lore.kernel.org/r/20210306054040.76483-1-mailhol.vincent@wanadoo.fr Signed-off-by: Vincent Mailhol Signed-off-by: Marc Kleine-Budde