Re: CM-ITC, pch_can/c_can_pci, sendto() returning ENOBUFS

[Jacob Kroon <jacob.kroon@gmail.com>]

Hi Wolfgang and Marc,

On 8/29/22 11:14, Jacob Kroon wrote:
> On 8/26/22 13:24, Jacob Kroon wrote:
>> On 8/25/22 15:25, Jacob Kroon wrote:
>>> Hi,
>>>
>>> I am using a CM-ITC board 
>>> (https://www.compulab.com/products/computer-on-modules/cm-itc/) with 
>>> an application that uses the CAN interface. After a while of 
>>> successfully sending packets, sendto() starts returning ENOBUFS. I 
>>> wait a whole second and try to send, several retries, but I get 
>>> ENOBUFS every time. I'm using kernel 5.15.59, and I've tried both the 
>>> pch_can and c_can_pci driver, but both show the same error.
>>>
>>> In the console I see several of:
>>> can0: can_put_echo_skb: BUG! echo_skb 0 is occupied
>>>
>>> I've also tried to increase the txqueuelen to 1000, as suggested here
>>>
>>> https://stackoverflow.com/questions/40424433/write-no-buffer-space-available-socket-can-linux-can
>>>
>>> but I think that if I increase the queuelen the threads just block 
>>> forever in sendto() (sockets are opened in blocking mode)
>>>
>>> If I bring down the interface with
>>>
>>> ifconfig can0 down
>>> ifconfig can0 up
>>>
>>> the transmitting does get unblocked.
>>>
>>> Is there anything I can do to debug this further ? Any other ideas ?
>>>
>>
>> First I get the print:
>>
>> can_put_echo_skb: BUG! echo_skb 0 is occupied!
>>
>> then netif_stop_queue() is called from here:
>>
>> https://github.com/torvalds/linux/blob/master/drivers/net/can/c_can/c_can_main.c#L469
>>
>> and then there is no call to netif_start_queue(), so the bus hangs.
>>
> 
> Switching back to the pch_can driver. I'm guessing here but it would 
> seem that the driver is not receiving the TX interrupt for 
> 'PCH_TX_OBJ_END' that would wake up the netif queue, since with the 
> changes below I can't reproduce the hang, although I'm still seeing a 
> lot of "echo_skb <x> is occupied!":
> 
>> diff --git a/drivers/net/can/pch_can.c b/drivers/net/can/pch_can.c
>> index 964c8a09226a..75ad2272d9b2 100644
>> --- a/drivers/net/can/pch_can.c
>> +++ b/drivers/net/can/pch_can.c
>> @@ -719,8 +720,7 @@ static void pch_can_tx_complete(struct net_device 
>> *ndev, u32 int_stat)
>>                           PCH_IF_MCONT_DLC);
>>         stats->tx_bytes += dlc;
>>         stats->tx_packets++;
>> -       if (int_stat == PCH_TX_OBJ_END)
>> -               netif_wake_queue(ndev);
>> +       netif_wake_queue(ndev);
>>  }
> 

Is there a recommended driver for the Intel EG20T PCH CAN controller ? 
pch_can or c_can_pci ?

Jacob