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Message-Id: <20251013-canxl-netlink-v1-8-f422b7e2729f@kernel.org>
Date: Mon, 13 Oct 2025 20:01:30 +0900
From: Vincent Mailhol <mailhol@...nel.org>
To: Marc Kleine-Budde <mkl@...gutronix.de>,
Oliver Hartkopp <socketcan@...tkopp.net>
Cc: Vincent Mailhol <mailhol@...nel.org>,
Stéphane Grosjean <stephane.grosjean@...-networks.com>,
Robert Nawrath <mbro1689@...il.com>, Minh Le <minh.le.aj@...esas.com>,
Duy Nguyen <duy.nguyen.rh@...esas.com>, linux-can@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 8/9] can: calc_bittiming: add PWM calculation
Perform the PWM calculation according to CiA recommendations.
Note that for databitrates greater than 5 MBPS, tqmin is less than
CAN_PWM_NS_MAX (which is defined to 200 nano seconds), consequently,
the result of the division:
DIV_ROUND_UP(xl_ns, CAN_PWM_NS_MAX)
is one and thus the for loop automatically stops on the first
iteration giving a single PWM symbol per bit as expected. Because of
that, there is no actual need for a separate conditional branch for
when the databitrate is greater than 5 MBPS.
Signed-off-by: Vincent Mailhol <mailhol@...nel.org>
---
drivers/net/can/dev/calc_bittiming.c | 36 ++++++++++++++++++++++++++++++++++++
include/linux/can/bittiming.h | 7 +++++++
2 files changed, 43 insertions(+)
diff --git a/drivers/net/can/dev/calc_bittiming.c b/drivers/net/can/dev/calc_bittiming.c
index 394d6974f481..268ec6fa7c49 100644
--- a/drivers/net/can/dev/calc_bittiming.c
+++ b/drivers/net/can/dev/calc_bittiming.c
@@ -2,6 +2,7 @@
/* Copyright (C) 2005 Marc Kleine-Budde, Pengutronix
* Copyright (C) 2006 Andrey Volkov, Varma Electronics
* Copyright (C) 2008-2009 Wolfgang Grandegger <wg@...ndegger.com>
+ * Copyright (C) 2021-2025 Vincent Mailhol <mailhol@...nel.org>
*/
#include <linux/units.h>
@@ -198,3 +199,38 @@ void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
*ctrlmode |= tdc_auto;
}
}
+
+int can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack)
+{
+ struct can_priv *priv = netdev_priv(dev);
+ const struct can_pwm_const *pwm_const = priv->xl.pwm_const;
+ struct can_pwm *pwm = &priv->xl.pwm;
+ u32 xl_tqmin = can_bit_time_tqmin(&priv->xl.data_bittiming);
+ u32 xl_ns = can_tqmin_to_ns(xl_tqmin, priv->clock.freq);
+ u32 nom_tqmin = can_bit_time_tqmin(&priv->bittiming);
+ int pwm_per_bit_max = xl_tqmin / (pwm_const->pwms_min + pwm_const->pwml_min);
+ int pwm_per_bit;
+ u32 pwm_tqmin;
+
+ /* For 5 MB/s databitrate or greater, xl_ns < CAN_PWM_NS_MAX
+ * giving us a pwm_per_bit of 1 and the loop immediately breaks
+ */
+ for (pwm_per_bit = DIV_ROUND_UP(xl_ns, CAN_PWM_NS_MAX);
+ pwm_per_bit <= pwm_per_bit_max; pwm_per_bit++)
+ if (xl_tqmin % pwm_per_bit == 0)
+ break;
+
+ if (pwm_per_bit > pwm_per_bit_max) {
+ NL_SET_ERR_MSG_FMT(extack,
+ "Can not divide the XL data phase's bit time: %u tqmin into multiple PWM symbols",
+ xl_tqmin);
+ return -EINVAL;
+ }
+
+ pwm_tqmin = xl_tqmin / pwm_per_bit;
+ pwm->pwms = DIV_ROUND_UP_POW2(pwm_tqmin, 4);
+ pwm->pwml = pwm_tqmin - pwm->pwms;
+ pwm->pwmo = nom_tqmin % pwm_tqmin;
+
+ return 0;
+}
diff --git a/include/linux/can/bittiming.h b/include/linux/can/bittiming.h
index 02cf9541a1dd..e7671a86afcc 100644
--- a/include/linux/can/bittiming.h
+++ b/include/linux/can/bittiming.h
@@ -180,6 +180,8 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
const struct can_bittiming *dbt,
u32 tdc_mask, u32 *ctrlmode, u32 ctrlmode_supported);
+
+int can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack);
#else /* !CONFIG_CAN_CALC_BITTIMING */
static inline int
can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
@@ -195,6 +197,11 @@ can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
u32 tdc_mask, u32 *ctrlmode, u32 ctrlmode_supported)
{
}
+
+static inline int
+can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack)
+{
+}
#endif /* CONFIG_CAN_CALC_BITTIMING */
void can_sjw_set_default(struct can_bittiming *bt);
--
2.49.1
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