Commit 9892339c authored by Vincent Mailhol's avatar Vincent Mailhol Committed by Marc Kleine-Budde
Browse files

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: default avatarVincent Mailhol <mailhol@kernel.org>
Signed-off-by: default avatarOliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20251126-canxl-v8-10-e7e3eb74f889@pengutronix.de


Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent 8e2a2885

drivers/net/can/dev/calc_bittiming.c

+36 −0
Original line number Diff line number Diff line
@@ -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@grandegger.com>

 * Copyright (C) 2021-2025 Vincent Mailhol <mailhol@kernel.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;

}

include/linux/can/bittiming.h

+10 −0
Original line number Diff line number Diff line
@@ -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 +197,14 @@ 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)

{

	NL_SET_ERR_MSG(extack,

		       "bit-timing calculation not available: manually provide PWML and PWMS\n");

	return -EINVAL;

}

#endif /* CONFIG_CAN_CALC_BITTIMING */



void can_sjw_set_default(struct can_bittiming *bt);