Merge patch series "can: bittiming: cleanups and rework SJW handling"

Marc Kleine-Budde <mkl@pengutronix.de> says:

several people noticed that on modern CAN controllers with wide bit
timing registers the default SJW of 1 can result in unstable or no
synchronization to the CAN network. See Patch 14/17 for details.

During review of v1 Vincent pointed out that the original code and the
series doesn't always check user provided bit timing parameters,
sometimes silently limits them and the return error values are not
consistent.

This series first cleans up some code in bittiming.c, replacing
open-coded variants by macros or functions (Patches 1, 2).

Patch 3 adds the missing assignment of the effective TQ if the
interface is configured with low level timing parameters.

Patch 4 is another code cleanup.

Patches 5, 6 check the bit timing parameter during interface
registration.

Patch 7 adds a validation of the sample point.

The patches 8-13 convert the error messages from netdev_err() to
NL_SET_ERR_MSG_FMT, factor out the SJW handling from
can_fixup_bittiming(), add checking and error messages for the
individual limits and harmonize the error return values.

Patch 14 changes the default SJW value from 1 to min(Phase Seg1, Phase
Seg2 / 2).

Patch 15 switches can_calc_bittiming() to use the new SJW handling.

Patch 16 converts can_calc_bittiming() to NL_SET_ERR_MSG_FMT().

And patch 16 adds a NL_SET_ERR_MSG_FMT() error message to
can_validate_bitrate().

v1: https://lore.kernel.org/all/20220907103845.3929288-1-mkl@pengutronix.de

Link: https://lore.kernel.org/all/20230202110854.2318594-1-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev/bittiming.c

@@ -6,25 +6,81 @@
 
 #include <linux/can/dev.h>
 
+void can_sjw_set_default(struct can_bittiming *bt)
+{
+	if (bt->sjw)
+		return;
+
+	/* If user space provides no sjw, use sane default of phase_seg2 / 2 */
+	bt->sjw = max(1U, min(bt->phase_seg1, bt->phase_seg2 / 2));
+}
+
+int can_sjw_check(const struct net_device *dev, const struct can_bittiming *bt,
+		  const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
+{
+	if (bt->sjw > btc->sjw_max) {
+		NL_SET_ERR_MSG_FMT(extack, "sjw: %u greater than max sjw: %u",
+				   bt->sjw, btc->sjw_max);
+		return -EINVAL;
+	}
+
+	if (bt->sjw > bt->phase_seg1) {
+		NL_SET_ERR_MSG_FMT(extack,
+				   "sjw: %u greater than phase-seg1: %u",
+				   bt->sjw, bt->phase_seg1);
+		return -EINVAL;
+	}
+
+	if (bt->sjw > bt->phase_seg2) {
+		NL_SET_ERR_MSG_FMT(extack,
+				   "sjw: %u greater than phase-seg2: %u",
+				   bt->sjw, bt->phase_seg2);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 /* Checks the validity of the specified bit-timing parameters prop_seg,
  * phase_seg1, phase_seg2 and sjw and tries to determine the bitrate
  * prescaler value brp. You can find more information in the header
  * file linux/can/netlink.h.
  */
 static int can_fixup_bittiming(const struct net_device *dev, struct can_bittiming *bt,
-			       const struct can_bittiming_const *btc)
+			       const struct can_bittiming_const *btc,
+			       struct netlink_ext_ack *extack)
 {
+	const unsigned int tseg1 = bt->prop_seg + bt->phase_seg1;
 	const struct can_priv *priv = netdev_priv(dev);
-	unsigned int tseg1, alltseg;
 	u64 brp64;
+	int err;
 
-	tseg1 = bt->prop_seg + bt->phase_seg1;
-	if (!bt->sjw)
-		bt->sjw = 1;
-	if (bt->sjw > btc->sjw_max ||
-	    tseg1 < btc->tseg1_min || tseg1 > btc->tseg1_max ||
-	    bt->phase_seg2 < btc->tseg2_min || bt->phase_seg2 > btc->tseg2_max)
-		return -ERANGE;
+	if (tseg1 < btc->tseg1_min) {
+		NL_SET_ERR_MSG_FMT(extack, "prop-seg + phase-seg1: %u less than tseg1-min: %u",
+				   tseg1, btc->tseg1_min);
+		return -EINVAL;
+	}
+	if (tseg1 > btc->tseg1_max) {
+		NL_SET_ERR_MSG_FMT(extack, "prop-seg + phase-seg1: %u greater than tseg1-max: %u",
+				   tseg1, btc->tseg1_max);
+		return -EINVAL;
+	}
+	if (bt->phase_seg2 < btc->tseg2_min) {
+		NL_SET_ERR_MSG_FMT(extack, "phase-seg2: %u less than tseg2-min: %u",
+				   bt->phase_seg2, btc->tseg2_min);
+		return -EINVAL;
+	}
+	if (bt->phase_seg2 > btc->tseg2_max) {
+		NL_SET_ERR_MSG_FMT(extack, "phase-seg2: %u greater than tseg2-max: %u",
+				   bt->phase_seg2, btc->tseg2_max);
+		return -EINVAL;
+	}
+
+	can_sjw_set_default(bt);
+
+	err = can_sjw_check(dev, bt, btc, extack);
+	if (err)
+		return err;
 
 	brp64 = (u64)priv->clock.freq * (u64)bt->tq;
 	if (btc->brp_inc > 1)
@@ -35,12 +91,21 @@ static int can_fixup_bittiming(const struct net_device *dev, struct can_bittimin
 		brp64 *= btc->brp_inc;
 	bt->brp = (u32)brp64;
 
-	if (bt->brp < btc->brp_min || bt->brp > btc->brp_max)
+	if (bt->brp < btc->brp_min) {
+		NL_SET_ERR_MSG_FMT(extack, "resulting brp: %u less than brp-min: %u",
+				   bt->brp, btc->brp_min);
+		return -EINVAL;
+	}
+	if (bt->brp > btc->brp_max) {
+		NL_SET_ERR_MSG_FMT(extack, "resulting brp: %u greater than brp-max: %u",
+				   bt->brp, btc->brp_max);
 		return -EINVAL;
+	}
 
-	alltseg = bt->prop_seg + bt->phase_seg1 + bt->phase_seg2 + 1;
-	bt->bitrate = priv->clock.freq / (bt->brp * alltseg);
-	bt->sample_point = ((tseg1 + 1) * 1000) / alltseg;
+	bt->bitrate = priv->clock.freq / (bt->brp * can_bit_time(bt));
+	bt->sample_point = ((CAN_SYNC_SEG + tseg1) * 1000) / can_bit_time(bt);
+	bt->tq = DIV_U64_ROUND_CLOSEST(mul_u32_u32(bt->brp, NSEC_PER_SEC),
+				       priv->clock.freq);
 
 	return 0;
 }
@@ -49,7 +114,8 @@ static int can_fixup_bittiming(const struct net_device *dev, struct can_bittimin
 static int
 can_validate_bitrate(const struct net_device *dev, const struct can_bittiming *bt,
 		     const u32 *bitrate_const,
-		     const unsigned int bitrate_const_cnt)
+		     const unsigned int bitrate_const_cnt,
+		     struct netlink_ext_ack *extack)
 {
 	unsigned int i;
 
@@ -58,30 +124,30 @@ can_validate_bitrate(const struct net_device *dev, const struct can_bittiming *b
 			return 0;
 	}
 
+	NL_SET_ERR_MSG_FMT(extack, "bitrate %u bps not supported",
+			   bt->brp);
+
 	return -EINVAL;
 }
 
 int can_get_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 		      const struct can_bittiming_const *btc,
 		      const u32 *bitrate_const,
-		      const unsigned int bitrate_const_cnt)
+		      const unsigned int bitrate_const_cnt,
+		      struct netlink_ext_ack *extack)
 {
-	int err;
-
 	/* Depending on the given can_bittiming parameter structure the CAN
 	 * timing parameters are calculated based on the provided bitrate OR
 	 * alternatively the CAN timing parameters (tq, prop_seg, etc.) are
 	 * provided directly which are then checked and fixed up.
 	 */
 	if (!bt->tq && bt->bitrate && btc)
-		err = can_calc_bittiming(dev, bt, btc);
-	else if (bt->tq && !bt->bitrate && btc)
-		err = can_fixup_bittiming(dev, bt, btc);
-	else if (!bt->tq && bt->bitrate && bitrate_const)
-		err = can_validate_bitrate(dev, bt, bitrate_const,
-					   bitrate_const_cnt);
-	else
-		err = -EINVAL;
-
-	return err;
+		return can_calc_bittiming(dev, bt, btc, extack);
+	if (bt->tq && !bt->bitrate && btc)
+		return can_fixup_bittiming(dev, bt, btc, extack);
+	if (!bt->tq && bt->bitrate && bitrate_const)
+		return can_validate_bitrate(dev, bt, bitrate_const,
+					    bitrate_const_cnt, extack);
+
+	return -EINVAL;
 }

drivers/net/can/dev/calc_bittiming.c

@@ -63,7 +63,7 @@ can_update_sample_point(const struct can_bittiming_const *btc,
 }
 
 int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
-		       const struct can_bittiming_const *btc)
+		       const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
 {
 	struct can_priv *priv = netdev_priv(dev);
 	unsigned int bitrate;			/* current bitrate */
@@ -76,6 +76,7 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 	unsigned int best_brp = 0;		/* current best value for brp */
 	unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
 	u64 v64;
+	int err;
 
 	/* Use CiA recommended sample points */
 	if (bt->sample_point) {
@@ -133,13 +134,14 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 		do_div(v64, bt->bitrate);
 		bitrate_error = (u32)v64;
 		if (bitrate_error > CAN_CALC_MAX_ERROR) {
-			netdev_err(dev,
-				   "bitrate error %d.%d%% too high\n",
-				   bitrate_error / 10, bitrate_error % 10);
-			return -EDOM;
+			NL_SET_ERR_MSG_FMT(extack,
+					   "bitrate error: %u.%u%% too high",
+					   bitrate_error / 10, bitrate_error % 10);
+			return -EINVAL;
 		}
-		netdev_warn(dev, "bitrate error %d.%d%%\n",
-			    bitrate_error / 10, bitrate_error % 10);
+		NL_SET_ERR_MSG_FMT(extack,
+				   "bitrate error: %u.%u%%",
+				   bitrate_error / 10, bitrate_error % 10);
 	}
 
 	/* real sample point */
@@ -154,23 +156,17 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 	bt->phase_seg1 = tseg1 - bt->prop_seg;
 	bt->phase_seg2 = tseg2;
 
-	/* check for sjw user settings */
-	if (!bt->sjw || !btc->sjw_max) {
-		bt->sjw = 1;
-	} else {
-		/* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */
-		if (bt->sjw > btc->sjw_max)
-			bt->sjw = btc->sjw_max;
-		/* bt->sjw must not be higher than tseg2 */
-		if (tseg2 < bt->sjw)
-			bt->sjw = tseg2;
-	}
+	can_sjw_set_default(bt);
+
+	err = can_sjw_check(dev, bt, btc, extack);
+	if (err)
+		return err;
 
 	bt->brp = best_brp;
 
 	/* real bitrate */
 	bt->bitrate = priv->clock.freq /
-		(bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2));
+		(bt->brp * can_bit_time(bt));
 
 	return 0;
 }

drivers/net/can/dev/dev.c

@@ -498,6 +498,18 @@ static int can_get_termination(struct net_device *ndev)
 	return 0;
 }
 
+static bool
+can_bittiming_const_valid(const struct can_bittiming_const *btc)
+{
+	if (!btc)
+		return true;
+
+	if (!btc->sjw_max)
+		return false;
+
+	return true;
+}
+
 /* Register the CAN network device */
 int register_candev(struct net_device *dev)
 {
@@ -518,6 +530,15 @@ int register_candev(struct net_device *dev)
 	if (!priv->data_bitrate_const != !priv->data_bitrate_const_cnt)
 		return -EINVAL;
 
+	/* We only support either fixed bit rates or bit timing const. */
+	if ((priv->bitrate_const || priv->data_bitrate_const) &&
+	    (priv->bittiming_const || priv->data_bittiming_const))
+		return -EINVAL;
+
+	if (!can_bittiming_const_valid(priv->bittiming_const) ||
+	    !can_bittiming_const_valid(priv->data_bittiming_const))
+		return -EINVAL;
+
 	if (!priv->termination_const) {
 		err = can_get_termination(dev);
 		if (err)

drivers/net/can/dev/netlink.c

@@ -36,10 +36,24 @@ static const struct nla_policy can_tdc_policy[IFLA_CAN_TDC_MAX + 1] = {
 	[IFLA_CAN_TDC_TDCF] = { .type = NLA_U32 },
 };
 
+static int can_validate_bittiming(const struct can_bittiming *bt,
+				  struct netlink_ext_ack *extack)
+{
+	/* sample point is in one-tenth of a percent */
+	if (bt->sample_point >= 1000) {
+		NL_SET_ERR_MSG(extack, "sample point must be between 0 and 100%");
+
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int can_validate(struct nlattr *tb[], struct nlattr *data[],
 			struct netlink_ext_ack *extack)
 {
 	bool is_can_fd = false;
+	int err;
 
 	/* Make sure that valid CAN FD configurations always consist of
 	 * - nominal/arbitration bittiming
@@ -51,6 +65,15 @@ static int can_validate(struct nlattr *tb[], struct nlattr *data[],
 	if (!data)
 		return 0;
 
+	if (data[IFLA_CAN_BITTIMING]) {
+		struct can_bittiming bt;
+
+		memcpy(&bt, nla_data(data[IFLA_CAN_BITTIMING]), sizeof(bt));
+		err = can_validate_bittiming(&bt, extack);
+		if (err)
+			return err;
+	}
+
 	if (data[IFLA_CAN_CTRLMODE]) {
 		struct can_ctrlmode *cm = nla_data(data[IFLA_CAN_CTRLMODE]);
 		u32 tdc_flags = cm->flags & CAN_CTRLMODE_TDC_MASK;
@@ -71,7 +94,6 @@ static int can_validate(struct nlattr *tb[], struct nlattr *data[],
 		 */
 		if (data[IFLA_CAN_TDC]) {
 			struct nlattr *tb_tdc[IFLA_CAN_TDC_MAX + 1];
-			int err;
 
 			err = nla_parse_nested(tb_tdc, IFLA_CAN_TDC_MAX,
 					       data[IFLA_CAN_TDC],
@@ -102,6 +124,15 @@ static int can_validate(struct nlattr *tb[], struct nlattr *data[],
 			return -EOPNOTSUPP;
 	}
 
+	if (data[IFLA_CAN_DATA_BITTIMING]) {
+		struct can_bittiming bt;
+
+		memcpy(&bt, nla_data(data[IFLA_CAN_DATA_BITTIMING]), sizeof(bt));
+		err = can_validate_bittiming(&bt, extack);
+		if (err)
+			return err;
+	}
+
 	return 0;
 }
 
@@ -184,13 +215,15 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
 		err = can_get_bittiming(dev, &bt,
 					priv->bittiming_const,
 					priv->bitrate_const,
-					priv->bitrate_const_cnt);
+					priv->bitrate_const_cnt,
+					extack);
 		if (err)
 			return err;
 
 		if (priv->bitrate_max && bt.bitrate > priv->bitrate_max) {
-			netdev_err(dev, "arbitration bitrate surpasses transceiver capabilities of %d bps\n",
-				   priv->bitrate_max);
+			NL_SET_ERR_MSG_FMT(extack,
+					   "arbitration bitrate %u bps surpasses transceiver capabilities of %u bps",
+					   bt.bitrate, priv->bitrate_max);
 			return -EINVAL;
 		}
 
@@ -288,13 +321,15 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
 		err = can_get_bittiming(dev, &dbt,
 					priv->data_bittiming_const,
 					priv->data_bitrate_const,
-					priv->data_bitrate_const_cnt);
+					priv->data_bitrate_const_cnt,
+					extack);
 		if (err)
 			return err;
 
 		if (priv->bitrate_max && dbt.bitrate > priv->bitrate_max) {
-			netdev_err(dev, "canfd data bitrate surpasses transceiver capabilities of %d bps\n",
-				   priv->bitrate_max);
+			NL_SET_ERR_MSG_FMT(extack,
+					   "CANFD data bitrate %u bps surpasses transceiver capabilities of %u bps",
+					   dbt.bitrate, priv->bitrate_max);
 			return -EINVAL;
 		}
 

include/linux/can/bittiming.h

@@ -116,7 +116,7 @@ struct can_tdc_const {
 
 #ifdef CONFIG_CAN_CALC_BITTIMING
 int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
-		       const struct can_bittiming_const *btc);
+		       const struct can_bittiming_const *btc, struct netlink_ext_ack *extack);
 
 void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
 		   const struct can_bittiming *dbt,
@@ -138,10 +138,16 @@ can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
 }
 #endif /* CONFIG_CAN_CALC_BITTIMING */
 
+void can_sjw_set_default(struct can_bittiming *bt);
+
+int can_sjw_check(const struct net_device *dev, const struct can_bittiming *bt,
+		  const struct can_bittiming_const *btc, struct netlink_ext_ack *extack);
+
 int can_get_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 		      const struct can_bittiming_const *btc,
 		      const u32 *bitrate_const,
-		      const unsigned int bitrate_const_cnt);
+		      const unsigned int bitrate_const_cnt,
+		      struct netlink_ext_ack *extack);
 
 /*
  * can_bit_time() - Duration of one bit