[canxl v3 12/17] can: calc_bittiming: add can_calc_sample_point_nrz()

Oliver Hartkopp
2025-11-20T18:45:41Z

CAN XL optimal sample point for PWM encoding (when TMS is on) differs
from the NRZ optimal one. There is thus a need to calculate a
different sample point depending whether TMS is on or off.

This is a preparation change: move the sample point calculation from
can_calc_bittiming() into the new can_calc_sample_point_nrz()
function.

In an upcoming change, a function will be added to calculate the
sample point for PWM encoding.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
drivers/net/can/dev/calc_bittiming.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/net/can/dev/calc_bittiming.c b/drivers/net/can/dev/calc_bittiming.c
index 46f6f5942abb..35db90be9c9a 100644
--- a/drivers/net/can/dev/calc_bittiming.c
+++ b/drivers/net/can/dev/calc_bittiming.c
@@ -8,10 +8,22 @@
#include <linux/units.h>
#include <linux/can/dev.h>

#define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */

+/* CiA recommended sample points for Non Return to Zero encoding. */
+static int can_calc_sample_point_nrz(const struct can_bittiming *bt)
+{
+ if (bt->bitrate > 800 * KILO /* BPS */)
+ return 750;
+
+ if (bt->bitrate > 500 * KILO /* BPS */)
+ return 800;
+
+ return 875;
+}
+
/* Bit-timing calculation derived from:
*
* Code based on LinCAN sources and H8S2638 project
* Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz
* Copyright 2005 Stanislav Marek
@@ -76,21 +88,14 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
unsigned int best_brp = 0; /* current best value for brp */
unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
u64 v64;
int err;

- /* Use CiA recommended sample points */
- if (bt->sample_point) {
+ if (bt->sample_point)
sample_point = bt->sample_point;
- } else {
- if (bt->bitrate > 800 * KILO /* BPS */)
- sample_point = 750;
- else if (bt->bitrate > 500 * KILO /* BPS */)
- sample_point = 800;
- else
- sample_point = 875;
- }
+ else
+ sample_point = can_calc_sample_point_nrz(bt);

/* tseg even = round down, odd = round up */
for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
tsegall = CAN_SYNC_SEG + tseg / 2;
--
2.47.3