On 04/30/2017 01:33 PM, Mirea, Bogdan-Stefan wrote:
> Hello Marc,
>
>> On 04/29/2017 09:48 PM, Bogdan Mirea wrote:
>>> Added rcar_can_set_bittiming as can.do_set_bittiming callback that
>>> will be called from can_changelink generic callback when link state
>>> is
>>> changed.
>>>
>>> This enables set bittiming support:
>>> ip link set can0 type can bitrate 500000 triple-sampling on
>>
>> Why is this needed? rcar_can_set_bittiming() is called during
>> rcar_can_open().
>
> I know that rcar_can_set_bittiming() is called during rcar_can_open()
> and setting bittiming works fine when setting can up with a command
> like:
> (1st approah)
> $ip link set can0 up type can bitrate 500000
>
> But most of tutorials online[1] are presenting as a TODO the following
> pair of commands:
> (2nd approah)
> $ip link set can0 type can bitrate 500000
> $ip link set up can0
>
> And in this 2nd approah, the first command will fail since it will call
> can_changelink which on its turn will try calling .do_set_bittiming
> callback and the former callback is not defined for rcar_can.
Why should it fail?
> memcpy(&bt, nla_data(data[IFLA_CAN_BITTIMING]), sizeof(bt));
> err = can_get_bittiming(dev, &bt,
> priv->bittiming_const,
> priv->bitrate_const,
> priv->bitrate_const_cnt);
> if (err)
> return err;
> memcpy(&priv->bittiming, &bt, sizeof(bt));
Here the bittiming settings are copied to priv->bittiming
>
> if (priv->do_set_bittiming) {
> /* Finally, set the bit-timing registers */
> err = priv->do_set_bittiming(dev);
> if (err)
> return err;
> }
and it will only call the set_bittiming if it's defined.
> I don't say this is a must-have feature, since calling iproute2 with
> "set bitrate" and "set can up" as in 1st approach will work just fine,
> will work just fine, but it is a nice to have feature for the second
> approach of setting bitrate.
> Also peak_usb pcan[2] uses this second approach (the changelink one) and
> this patch updates rcar_can for it.
Sorry I still don't get why this is necessary.
Marc
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Pengutronix e.K. | Marc Kleine-Budde |
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