linux-kernel - Re: [PATCH v5 2/5] can: kvaser_usb: Consolidate and unify state change handling

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Date:	Wed, 21 Jan 2015 10:36:47 -0500
From:	"Ahmed S. Darwish" <darwish.07@...il.com>
To:	Andri Yngvason <andri.yngvason@...el.com>
Cc:	Wolfgang Grandegger <wg@...ndegger.com>,
	Olivier Sobrie <olivier@...rie.be>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Linux-CAN <linux-can@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/5] can: kvaser_usb: Consolidate and unify state
 change handling

On Wed, Jan 21, 2015 at 03:00:15PM +0000, Andri Yngvason wrote:
> Quoting Ahmed S. Darwish (2015-01-21 14:43:23)
> > Hi!

...

> > <-- Unplug the cable -->
> > 
> >  (000.009106)  can0  20000080   [8]  00 00 00 00 00 00 08 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{8}{0}}
> >  (000.001872)  can0  20000080   [8]  00 00 00 00 00 00 10 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{16}{0}}
> [...]
> >         error-counter-tx-rx{{80}{0}}
> >  (000.001910)  can0  20000080   [8]  00 00 00 00 00 00 58 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{88}{0}}
> >  (000.001753)  can0  20000084   [8]  00 08 00 00 00 00 60 00   ERRORFRAME
> >         controller-problem{tx-error-warning}
> Good.
> >         bus-error
> >         error-counter-tx-rx{{96}{0}}

Nice.

> >  (000.001720)  can0  20000080   [8]  00 00 00 00 00 00 68 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{104}{0}}
> >  (000.001876)  can0  20000080   [8]  00 00 00 00 00 00 70 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{112}{0}}
> >  (000.001749)  can0  20000080   [8]  00 00 00 00 00 00 78 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{120}{0}}
> >  (000.001771)  can0  20000084   [8]  00 20 00 00 00 00 80 00   ERRORFRAME
> >         controller-problem{tx-error-passive}
> Also good.
> >         bus-error
> >         error-counter-tx-rx{{128}{0}}

Also nice :-)

> >  (000.001868)  can0  20000080   [8]  00 00 00 00 00 00 80 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{128}{0}}
> >  (000.001982)  can0  20000080   [8]  00 00 00 00 00 00 80 00   ERRORFRAME
> >         bus-error
> >         error-counter-tx-rx{{128}{0}}
> > 
> > (( Then a continous flood, exactly similar to the above packet, appears.
> >    Unfortunately this flooding is a firmware problem. ))
> > 
> > <-- Replug the cable, after a good amount of time -->
> >
> Where are the reverse state transitions?
> > 

Hmmm...

[ ... ]
> 
> Reverse state transitions are missing from the logs. See comments above.
> 

When the device is on the _receiving_ end, and I unplug the CAN cable after
introducing some noise to the level of reaching WARNING or PASSIVE, I
receive a BUS_ERROR event with the rxerr count reset back to 0 or 1. In
that case, the driver correctly transitions back the state to ERROR_ACTIVE
and candump produces something similar to:

    (000.000362)  can0  2000008C   [8]  00 40 40 00 00 00 00 01   ERRORFRAME
    controller-problem{}
    protocol-violation{{back-to-error-active}{}}
    bus-error
    error-counter-tx-rx{{0}{1}}

which is, AFAIK, the correct behaviour from the driver side.

Meanwhile, when the device is on the _sending_ end and I re-plug the CAN
cable again. Sometimes I receive events with txerr reset to 0 or 1, and
the driver correctly reverts back to ERROR_ACTIVE in that case. But on
another times like the quoted case above, I don't receive any events
resetting txerr back -- only data packets on the bus.

So, What can the driver do given the above?

Thanks,
Darwish

P.S. just in case, I'll also re-check now if the driver unintentionally
drops any important events resetting the txerr count back after a CAN
cable replug -- preventing the code from returning to ERROR_ACTIVE in
the process.

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