linux-kernel - [PATCH RFC 1/3] can: calc_bittiming: get rid of the incorrect "nominal" word

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Message-Id: <20251102-pwm_sample_point-v1-1-3bbea180f59e@kernel.org>
Date: Sun, 02 Nov 2025 23:01:22 +0100
From: Vincent Mailhol <mailhol@...nel.org>
To: Marc Kleine-Budde <mkl@...gutronix.de>, 
 Oliver Hartkopp <socketcan@...tkopp.net>
Cc: linux-can@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Vincent Mailhol <mailhol@...nel.org>
Subject: [PATCH RFC 1/3] can: calc_bittiming: get rid of the incorrect
 "nominal" word

The functions can_update_sample_point() and can_calc_bittiming() are
generic and meant to be used for both the nominal and the data
bittiming calculation.

However, those functions use terminologies such as "bitrate nominal"
or "sample point nominal". This is a leftover from when only Classical
CAN was supported and now became incorrect.

Remove or replace any occurrences of the word "nominal" with something
more accurate.

Signed-off-by: Vincent Mailhol <mailhol@...nel.org>
---
 drivers/net/can/dev/calc_bittiming.c | 30 ++++++++++++++----------------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/drivers/net/can/dev/calc_bittiming.c b/drivers/net/can/dev/calc_bittiming.c
index 268ec6fa7c49..222117596704 100644
--- a/drivers/net/can/dev/calc_bittiming.c
+++ b/drivers/net/can/dev/calc_bittiming.c
@@ -24,7 +24,7 @@
  */
 static int
 can_update_sample_point(const struct can_bittiming_const *btc,
-			const unsigned int sample_point_nominal, const unsigned int tseg,
+			unsigned int sp_origin, unsigned int tseg,
 			unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
 			unsigned int *sample_point_error_ptr)
 {
@@ -35,8 +35,7 @@ can_update_sample_point(const struct can_bittiming_const *btc,
 
 	for (i = 0; i <= 1; i++) {
 		tseg2 = tseg + CAN_SYNC_SEG -
-			(sample_point_nominal * (tseg + CAN_SYNC_SEG)) /
-			1000 - i;
+			(sp_origin * (tseg + CAN_SYNC_SEG)) / 1000 - i;
 		tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max);
 		tseg1 = tseg - tseg2;
 		if (tseg1 > btc->tseg1_max) {
@@ -46,9 +45,9 @@ can_update_sample_point(const struct can_bittiming_const *btc,
 
 		sample_point = 1000 * (tseg + CAN_SYNC_SEG - tseg2) /
 			(tseg + CAN_SYNC_SEG);
-		sample_point_error = abs(sample_point_nominal - sample_point);
+		sample_point_error = abs(sp_origin - sample_point);
 
-		if (sample_point <= sample_point_nominal &&
+		if (sample_point <= sp_origin &&
 		    sample_point_error < best_sample_point_error) {
 			best_sample_point = sample_point;
 			best_sample_point_error = sample_point_error;
@@ -68,11 +67,11 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 {
 	struct can_priv *priv = netdev_priv(dev);
 	unsigned int bitrate;			/* current bitrate */
-	unsigned int bitrate_error;		/* difference between current and nominal value */
+	unsigned int bitrate_error;		/* difference between current and calculated value */
 	unsigned int best_bitrate_error = UINT_MAX;
-	unsigned int sample_point_error;	/* difference between current and nominal value */
+	unsigned int sample_point_error;	/* difference between current and calculated value */
 	unsigned int best_sample_point_error = UINT_MAX;
-	unsigned int sample_point_nominal;	/* nominal sample point */
+	unsigned int sample_point;
 	unsigned int best_tseg = 0;		/* current best value for tseg */
 	unsigned int best_brp = 0;		/* current best value for brp */
 	unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
@@ -81,14 +80,14 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 
 	/* Use CiA recommended sample points */
 	if (bt->sample_point) {
-		sample_point_nominal = bt->sample_point;
+		sample_point = bt->sample_point;
 	} else {
 		if (bt->bitrate > 800 * KILO /* BPS */)
-			sample_point_nominal = 750;
+			sample_point = 750;
 		else if (bt->bitrate > 500 * KILO /* BPS */)
-			sample_point_nominal = 800;
+			sample_point = 800;
 		else
-			sample_point_nominal = 875;
+			sample_point = 875;
 	}
 
 	/* tseg even = round down, odd = round up */
@@ -115,7 +114,7 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 		if (bitrate_error < best_bitrate_error)
 			best_sample_point_error = UINT_MAX;
 
-		can_update_sample_point(btc, sample_point_nominal, tseg / 2,
+		can_update_sample_point(btc, sample_point, tseg / 2,
 					&tseg1, &tseg2, &sample_point_error);
 		if (sample_point_error >= best_sample_point_error)
 			continue;
@@ -146,9 +145,8 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 	}
 
 	/* real sample point */
-	bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
-						   best_tseg, &tseg1, &tseg2,
-						   NULL);
+	bt->sample_point = can_update_sample_point(btc, sample_point, best_tseg,
+						   &tseg1, &tseg2, NULL);
 
 	v64 = (u64)best_brp * 1000 * 1000 * 1000;
 	do_div(v64, priv->clock.freq);

-- 
2.51.0