Re: at91_can.c: Data transmission stops

[Wolfgang Grandegger <wg@grandegger.com>]

On 11/28/2012 03:56 PM, Marc Kleine-Budde wrote:
> On 11/27/2012 05:31 PM, Wolfgang Grandegger wrote:
> [...]
> 
>> As mentioned above, on the c_can there is definitely a race with the
>> message ram due to the busy wait after accessing it. See:
>>
>>   http://lxr.linux.no/#linux+v3.6.8/drivers/net/can/c_can/c_can.c#L237
>>
>>> Or is it the potential race between "c_can_start_xmit" and "c_can_do_tx" ?
>>> Or even the access to the net api?
>>>
>>> Would someone care to explain?
>>
>> I will try. In at91_start_xmit, if we get interrupted
>>
>> 	if (!(at91_read(priv, AT91_MSR(get_tx_next_mb(priv))) &
>>               AT91_MSR_MRDY) ||
>>              (priv->tx_next & get_next_mask(priv)) == 0)
>>
>> 		/* HERE */
>>
>> 		netif_stop_queue(dev);
>>
>> and then at91_irq_tx() is called executing netif_wake_queue() we may end
>> up with a stopped tx queue. But I'm not yet 100% sure.
> 
> I don't think so, because after this follows[1]
> 
> 	/* Enable interrupt for this mailbox */
> 	at91_write(priv, AT91_IER, 1 << mb);
> 
> [1] http://lxr.free-electrons.com/source/drivers/net/can/at91_can.c#L524
> 
> So first the queued ist stopped, then the interrupt activated.

OK, if not the interrupt of another mailbox does occur before the queue
gets stopped. May that happen?

Wolfgang.