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

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

[Oliver Hartkopp]

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-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>

---

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));

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

[Wolfgang Grandegger]

Hi Oliver,

On 09/22/2011 12:24 PM, Oliver Hartkopp wrote:
> 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-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
> 
> ---
> 
> 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;
> +	}
> +


Hm, bt->sjw is always 0 when can_calc_bittiming() is called!? Or have I
missed something.

Wolfgang,