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@hartkopp.net>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 9bf1116e5b5e..25695bde0549 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));