Hello Oliver,

On 12/2/20 3:35 PM, Oliver Hartkopp wrote:

On 27.11.20 12:09, Jeroen Hofstee wrote:

quoted

On 11/27/20 11:30 AM, Marc Kleine-Budde wrote:

quoted

On 11/27/20 10:59 AM, Jeroen Hofstee wrote:

quoted

Losing arbitration is normal in a CAN-bus network, it means that a
higher priority frame is being send and the pending message will be
retried later. Hence most driver only increment arbitration_lost, but
the sja1000 and sun4i driver also incremeant tx_error, causing errors
to be reported on a normal functioning CAN-bus. So stop counting them
as errors.

Sounds plausible.

quoted

For completeness, the Kvaser USB hybra also increments the tx_error
on arbitration lose, but it does so in single shot. Since in that
case the message is not retried, that behaviour is kept.

You mean only in one shot mode?

Yes, well at least the function is called 
kvaser_usb_hydra_one_shot_fail.

quoted

  What about one shot mode on the sja1000 cores?

That is a good question. I guess it will be counted as error by:

         if (isrc & IRQ_TI) {
             /* transmission buffer released */
             if (priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT &&
                 !(status & SR_TCS)) {
                 stats->tx_errors++;

I can confirm with CAN_CTRLMODE_ONE_SHOT active and the patch ("can: 
sja1000: sja1000_err(): don't count arbitration lose as an error")

https://git.kernel.org/pub/scm/linux/kernel/git/mkl/linux-can.git/commit/?h=testing&id=bd0ccb92efb09c7da5b55162b283b42a93539ed7 


I now get ONE(!) increment for tx_errors and ONE increment in the 
arbitration-lost counter.

Before the above patch I had TWO tx_errors for each arbitration lost case.

Good, thanks for checking!

quoted

                 can_free_echo_skb(dev, 0);
             } else {
                 /* transmission complete */
                 stats->tx_bytes +=
                     priv->read_reg(priv, SJA1000_FI) & 0xf;
                 stats->tx_packets++;
                 can_get_echo_skb(dev, 0);
             }
             netif_wake_queue(dev);
             can_led_event(dev, CAN_LED_EVENT_TX);
         }

 From the datasheet, Transmit Interrupt:

"set; this bit is set whenever the transmit bufferstatus
changes from ‘0-to-1’ (released) and the TIE bit is set
within the interrupt enable register".

I cannot test it though, since I don't have a sja1000.

Do we agree that in one-shot mode both the tx_errors and the 
arbitration_lost counters are increased in the arbitration-lost case?

At least this would fit to the Kvaser USB behaviour.

I have no opinion about that. I just kept existing behavior.

And btw. I wondered if we should remove the check for 
CAN_CTRLMODE_ONE_SHOT here, as we ALWAYS should count a tx_error and 
drop the echo_skb when we have a TX-interrupt and TX-complete flag is 
zero.

So replace:

if (priv->can.ctrlmode & CAN_CTRLMODE_ONE_SHOT &&
                  !(status & SR_TCS)) {

with:

if (!(status & SR_TCS)) {

Any suggestions?

In theory, yes. But I can't think of a reason you would end
up there without CAN_CTRLMODE_ONE_SHOT being set.
Aborting the current transmission in non single shot mode
will get you there and incorrectly report the message as
transmitted, but that is not implemented afaik.

Regards,

Jeroen



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