can: calc_bittiming: add can_calc_sample_point_nrz()

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>
Link: https://patch.msgid.link/20251126-canxl-v8-13-e7e3eb74f889@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/dev/calc_bittiming.c b/drivers/net/can/dev/calc_bittiming.c
index c8c166b383cd6f796e1f4a3531950935992ae4b4..bacdf3b218d32c4a01809016c9007671e341691f 100644 (file)
--- a/drivers/net/can/dev/calc_bittiming.c
+++ b/drivers/net/can/dev/calc_bittiming.c
@@ -10,6 +10,18 @@
 
 #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
@@ -79,17 +91,10 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
        u64 v64;
        int err;
 
-       /* Use CiA recommended sample points */
-       if (bt->sample_point) {
+       if (bt->sample_point)
                sample_point_reference = bt->sample_point;
-       } else {
-               if (bt->bitrate > 800 * KILO /* BPS */)
-                       sample_point_reference = 750;
-               else if (bt->bitrate > 500 * KILO /* BPS */)
-                       sample_point_reference = 800;
-               else
-                       sample_point_reference = 875;
-       }
+       else
+               sample_point_reference = can_calc_sample_point_nrz(bt);
 
        /* tseg even = round down, odd = round up */
        for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;