linux-kernel - [PATCH can-next v8 17/17] can: dev: print bitrate error with two decimal digits

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Message-Id: <20251126-canxl-v8-17-e7e3eb74f889@pengutronix.de>
Date: Wed, 26 Nov 2025 11:16:18 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Marc Kleine-Budde <mkl@...gutronix.de>, 
 Vincent Mailhol <mailhol@...nel.org>, 
 Oliver Hartkopp <socketcan@...tkopp.net>
Cc: kernel@...gutronix.de, linux-can@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Stéphane Grosjean <stephane.grosjean@...-networks.com>
Subject: [PATCH can-next v8 17/17] can: dev: print bitrate error with two
 decimal digits

From: Oliver Hartkopp <socketcan@...tkopp.net>

Increase the resolution when printing the bitrate error and round-up the
value to 0.01% in the case the resolution would still provide values
which would lead to 0.00%.

Suggested-by: Vincent Mailhol <mailhol@...nel.org>
Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 drivers/net/can/dev/calc_bittiming.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/net/can/dev/calc_bittiming.c b/drivers/net/can/dev/calc_bittiming.c
index 60a505ce69de..cc4022241553 100644
--- a/drivers/net/can/dev/calc_bittiming.c
+++ b/drivers/net/can/dev/calc_bittiming.c
@@ -153,19 +153,22 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 	}
 
 	if (best_bitrate_error) {
-		/* Error in one-tenth of a percent */
-		v64 = (u64)best_bitrate_error * 1000;
+		/* Error in one-hundredth of a percent */
+		v64 = (u64)best_bitrate_error * 10000;
 		do_div(v64, bt->bitrate);
 		bitrate_error = (u32)v64;
+		/* print at least 0.01% if the error is smaller */
+		bitrate_error = max(bitrate_error, 1U);
 		if (bitrate_error > CAN_CALC_MAX_ERROR) {
 			NL_SET_ERR_MSG_FMT(extack,
-					   "bitrate error: %u.%u%% too high",
-					   bitrate_error / 10, bitrate_error % 10);
+					   "bitrate error: %u.%02u%% too high",
+					   bitrate_error / 100,
+					   bitrate_error % 100);
 			return -EINVAL;
 		}
 		NL_SET_ERR_MSG_FMT(extack,
-				   "bitrate error: %u.%u%%",
-				   bitrate_error / 10, bitrate_error % 10);
+				   "bitrate error: %u.%02u%%",
+				   bitrate_error / 100, bitrate_error % 100);
 	}
 
 	/* real sample point */

-- 
2.51.0