Re: flexcan napi poll and error frames

[Wolfgang Grandegger <wg@grandegger.com>]

On Fri, 24 Oct 2014 10:26:11 +0000, Andri Yngvason
<andri.yngvason@marel.com> wrote:
> Hi,
> 
> I was running some tests on my patches when I noticed the following:
> If I have 2 flexcan devices on the bus, each sending to the bus using
> cangen,and then I disconnect the cable to one of them, that device
> will enter"error-warning" state, but it will not continue on to
> "error-passive" as itshould.
> 
> However, when I reconnect the cable, I get the "error-passive" message
> followed by an "error-warning" and eventually "back-to-error-active".

Yes, I think I observed that behaviour as well as you can see here:
https://gitorious.org/linux-can/wg-linux-can-next/commit/bd3acb12dbb9551541d28ae8766c154d3cf6ed57.patch

> Notice the time differences:
> root@(none):~# candump -td -e can0,0~0,#FFFFFFFFFF
>  (000.000000)  can0  20000004   [8]  00 08 00 00 00 00 00 00  
ERRORFRAME
>         controller-problem{tx-error-warning}
>  (006.493209)  can0  20000004   [8]  00 40 00 00 00 00 00 00  
ERRORFRAME
>         controller-problem{back-to-error-active}
>  (002.701331)  can0  20000004   [8]  00 08 00 00 00 00 00 00  
ERRORFRAME
>         controller-problem{tx-error-warning}
>  (006.498567)  can0  20000004   [8]  00 20 00 00 00 00 00 00  
ERRORFRAME
>         controller-problem{tx-error-passive}
>  (000.013915)  can0  20000004   [8]  00 08 00 00 00 00 00 00  
ERRORFRAME
>         controller-problem{tx-error-warning}
>  (001.990695)  can0  20000004   [8]  00 40 00 00 00 00 00 00  
ERRORFRAME
>         controller-problem{back-to-error-active}
> 
> 
> I suspect that the problem is that the driver doesn't receive any
> interruptsother than the one for "error-passive" and so things
> won't "weigh" enoughfor napi. There seems to be some truth in this
> conjecture, because when Itried setting the napi weight to 1, the
> message got through.

Hm, why should it depend on NAPI. It does not delay messages for
a long time. I think the problem is that the state change is not
signalled my an interrupt but some time later when another event
(message) occurs.
 
> Another thing that I found peculiar was that I had to be sending on
> both devices for the error states to change to anything other than
> "error-warning".

Well, the error reporting on the SJA1000 is perfect... on all other
CAN controllers it's more or less worse.

Wolfgang.