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

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

Hi Marc and Dario,

On 9/21/22 09:47, Marc Kleine-Budde wrote:
> On 21.09.2022 09:25:41, dariobin@libero.it wrote:
>>> On 9/16/22 06:14, Jacob Kroon wrote:
>>> ...> What I do know is that if I revert commit:
>>>>
>>>> "can: c_can: cache frames to operate as a true FIFO"
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=387da6bc7a826cc6d532b1c0002b7c7513238d5f
>>>>
>>>> then everything looks good. I don't get any BUG messages, and the host
>>>> has been running overnight without problems, so it seems to have fixed
>>>> the network interface lockup as well.
>>
>> Here's what I think:
>> If one or more messages are cached, the controller has to transmit more frames
>> in the unit of time when they can be transmitted (IF_COMM_TXRQST), different from
>> when the transmission occurs directly on request from the user space. In the case
>> of cached data transmission I therefore think that the controller is more heavily
>> loaded. Can this shift the balance ?
>>
>>>
>>> I ran the kernel *with* the commit above, and also with the following patch:
>>>
>>>> diff --git a/drivers/net/can/c_can/c_can_main.c b/drivers/net/can/c_can/c_can_main.c
>>>> index 52671d1ea17d..4375dc70e21f 100644
>>>> --- a/drivers/net/can/c_can/c_can_main.c
>>>> +++ b/drivers/net/can/c_can/c_can_main.c
>>>> @@ -1,3 +1,4 @@
>>>> +#define DEBUG
>>>>   /*
>>>>    * CAN bus driver for Bosch C_CAN controller
>>>>    *
>>>> @@ -469,8 +470,15 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
>>>>   	if (c_can_get_tx_free(tx_ring) == 0)
>>>>   		netif_stop_queue(dev);
>>>>   
>>>> -	if (idx < c_can_get_tx_tail(tx_ring))
>>>> +	netdev_dbg(dev, "JAKR:%d:%d:%d:%d\n", idx,
>>>> +	                                      c_can_get_tx_head(tx_ring),
>>>> +	                                      c_can_get_tx_tail(tx_ring),
>>>> +	                                      c_can_get_tx_free(tx_ring));
>>>> +
>>>> +	if (idx < c_can_get_tx_tail(tx_ring)) {
>>>>   		cmd &= ~IF_COMM_TXRQST; /* Cache the message */
>>>> +		netdev_dbg(dev, "JAKR:Caching messages\n");
>>>> +	}
>>>>   
>>>>   	/* Store the message in the interface so we can call
>>>>   	 * can_put_echo_skb(). We must do this before we enable
>>>
>>> and I've uploaded the entire log I could capture from /dev/kmsg, right
>>> up to the hang, here:
>>>
>>> https://pastebin.com/6hvAcPc9
>>>
>>> What looks odd to me right from the start is that sometimes when idx
>>> rolls over to 0, and *only* when it rolls over to 0, the CAN frame gets
>>> cached because "idx < c_can_get_tx_tail(tx_ring)".
>>
>> If the message were not stored but transmitted, the order of transmission
>> would not be respected.
>>
>>>
>>> Is it possible there is some difference between c_can and d_can in how
>>> the HW buffers are working, which breaks the driver on my particular HW
>>> setup ?
>>>
>>
>> I tested the patch on a beaglebone board without encountering any problems.
>> There is also a version of the driver I submitted to Xenomai running on a custom
>> board without problems. But surely the setup and context is different from yours.
>>
>> What compatible are you using in your device tree?
>> I used "ti,am3352-d_can".
> 
> I think Jacob's board has a c_can core, while the beagle bone uses a
> d_can. Maybe there's a subtle difference between these cores?
> 
> Dario, do you have access to a real c_can core to test?
> 
> As reverting 387da6bc7a82 ("can: c_can: cache frames to operate as a
> true FIFO") helps to fix Jacob's problem, a temporary solution might be
> to only cache frames on d_can cores.
> 

Yes, mine is c_can, my hardware is

https://www.compulab.com/products/computer-on-modules/cm-itc/

which has a Intel Platform Controller Hub (PCH) EG20T that includes the 
CAN bus. A quick Google list the datasheet here:

https://www.versalogic.com/wp-content/themes/vsl-new/assets/resources/support/pdf/Intel_PCH_EG20T_Datasheet.pdf

Regards,
Jacob