Wolfgang Grandegger wrote:
> Hi Jan,
> 
> Jan Kiszka wrote:
>> Hi Wolfgang,
>>
>> fiddling with the CAN utils, I noticed the behaviour that rtcansend on
>> freshly registered but stopped devices simply blocks. And when you
>> meanwhile call rtcanconfig up on that device, rtcansend will continue to
>> block.
> 
> I see the expected behavior on stopped devices:
> 
>   bash-2.05b# rtcansend rtcan0
>   rt_dev_send: Network is down
> 
> This is, because the tx_sem is marked "destroyed" already when the
> device gets initialized. I wonder why your app blocks.

Unlikely, because the sem is _not_ marked destroyed on startup:

http://www.rts.uni-hannover.de/xenomai/lxr/source/ksrc/drivers/can/rtcan_dev.c#181

In case it makes a subtle difference: I tested with xeno_can_virt, but I
think I saw the same effect on real SJA1000 hw as well.

> 
>> The reason is that during startup of CAN devices the tx-semaphore is
>> re-initialised while it is already set up during device registration.
>> Re-init on an already initialised rtdm_sem is, say, undefined.
> 
> That makes definitely trouble. A CAN_MODE_START should only start the
> device if it's not active. The attached patch fixes this. Another
> possibility would be to force a CAN_MODE_STOP in case the device is
> already active (=restart).
> 
>> So rtdm_sem should better only be initialised/destroyed by the drivers.
>> Trying to send on a shut down CAN device could be catched differently,
>> e.g. via the device state. This likely needs more thoughts, take it as a
>> note that $something should be done.
> 
> With the fix above I do not see further problems with the existing
> implementation using the "destroyed" state to mark the device unavailable.

The problem of double init remains. I don't think that the sem state
should be used for encoding the CAN device state towards potential senders.

Jan

> 
> Wolfgang.
> 
> 
> ------------------------------------------------------------------------
> 
> + diff -u xenomai/ksrc/drivers/can/rtcan_raw_dev.c.TXSEM xenomai/ksrc/drivers/can/rtcan_raw_dev.c
> --- xenomai/ksrc/drivers/can/rtcan_raw_dev.c.TXSEM	2007-02-15 11:21:43.000000000 +0100
> +++ xenomai/ksrc/drivers/can/rtcan_raw_dev.c	2007-02-15 14:16:16.000000000 +0100
> @@ -193,7 +193,8 @@
>      switch (request) {
>      case SIOCSCANMODE:
>  	mode = (can_mode_t *)&ifr->ifr_ifru;
> -	if (dev->do_set_mode)
> +	if (dev->do_set_mode &&
> +	    !(*mode == CAN_MODE_START && CAN_STATE_OPERATING(dev->state)))
>  	    ret = dev->do_set_mode(dev, *mode, &lock_ctx);
>  	break;
>