From: Wolfgang Grandegger <wg-5Yr1BZd7O62+XT7JhA+gdA@public•gmane.org>
To: Oliver Hartkopp <socketcan-fJ+pQTUTwRTk1uMJSBkQmQ@public•gmane.org>
Cc: SocketCAN Core Mailing List
<socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public•gmane.org>,
Linux Netdev List
<netdev-u79uwXL29TY76Z2rM5mHXA@public•gmane.org>,
David Miller <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public•gmane.org>
Subject: Re: [PATCH net-next v2] candev: allow SJW user setting for bittiming calculation
Date: Thu, 22 Sep 2011 15:07:43 +0200 [thread overview]
Message-ID: <4E7B331F.3070801@grandegger.com> (raw)
In-Reply-To: <4E7B0DE6.9020807-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
Hi Oliver,
On 09/22/2011 12:28 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>
>
> ---
>
> 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;
> + }
> +
As I already said, I expected "bt->sjw" to be always 0 when
can_calc_bittiming() is called. But the software somehow allows to
preset "bt->sjw", which is not intended as the help of the ip utility shows:
$ ip link set can0 type can help
Usage: ip link set DEVICE type can
[ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
[ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
I actually hesitate to extend can_calc_bittiming(). I suggest using an
external tool to calculate proper bit-timing parameters and set them
with "ip link set DEVICE type can tq ...".
See also:
http://lxr.linux.no/#linux+v3.0.4/Documentation/networking/can.txt#L742
Wolfgang.
next prev parent reply other threads:[~2011-09-22 13:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-22 10:28 [PATCH net-next v2] candev: allow SJW user setting for bittiming calculation Oliver Hartkopp
[not found] ` <4E7B0DE6.9020807-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-22 13:07 ` Wolfgang Grandegger [this message]
[not found] ` <4E7B331F.3070801-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-22 16:26 ` Oliver Hartkopp
[not found] ` <4E7B61C8.8020506-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-22 18:10 ` Wolfgang Grandegger
[not found] ` <4E7B7A30.4030707-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-22 19:41 ` Oliver Hartkopp
[not found] ` <4E7B8F63.6060108-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-23 7:24 ` Wolfgang Grandegger
[not found] ` <4E7C3424.8030406-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-23 9:32 ` Pavel Pisa
[not found] ` <201109231132.49976.pisa-/N2ztlQkxE7Ub/6JBqosbQ@public.gmane.org>
2011-09-23 15:50 ` Oliver Hartkopp
2011-09-24 7:22 ` Wolfgang Grandegger
[not found] ` <4E7D8537.8010302-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
2011-09-27 17:32 ` Oliver Hartkopp
[not found] ` <4E8208B5.4050907-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
2011-09-27 20:04 ` Wolfgang Grandegger
2011-09-24 7:44 ` Wolfgang Grandegger
2011-09-27 20:05 ` Wolfgang Grandegger
2011-09-29 6:14 ` Kurt Van Dijck
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