netdev - [PATCH net-next v2] candev: allow SJW user setting for bittiming calculation

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Date:	Thu, 22 Sep 2011 12:28:54 +0200
From:	Oliver Hartkopp <socketcan@...tkopp.net>
To:	David Miller <davem@...emloft.net>
CC:	Linux Netdev List <netdev@...r.kernel.org>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	Pavel Píša <pisa@....felk.cvut.cz>,
	SocketCAN Core Mailing List <socketcan-core@...ts.berlios.de>
Subject: [PATCH net-next v2] candev: allow SJW user setting for bittiming
 calculation

This patch adds support for SJW user settings to not set the synchronization
jump width (SJW) to 1 in any case when using the in-kernel bittiming
calculation.

The ip-tool from iproute2 already supports to pass the user defined SJW
value. The given SJW value is sanitized with the controller specific sjw_max
and the calculated tseg2 value. As the SJW can have values up to 4 providing
this value will lead to the maximum possible SJW automatically. A higher SJW
allows higher controller oscillator tolerances.

Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.net>

---

v2: Resend due to wrong mail address header encoding.

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 9bf1116..25695bd 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -150,7 +150,19 @@ static int can_calc_bittiming(struct net_device *dev,
struct can_bittiming *bt)
 	bt->prop_seg = tseg1 / 2;
 	bt->phase_seg1 = tseg1 - bt->prop_seg;
 	bt->phase_seg2 = tseg2;
-	bt->sjw = 1;
+
+	/* 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;
+	}
+
 	bt->brp = best_brp;
 	/* real bit-rate */
 	bt->bitrate = priv->clock.freq / (bt->brp * (tseg1 + tseg2 + 1));

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