netdev - Re: [PATCH] can: don't count arbitration lose as an error

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Date:   Sun, 29 Nov 2020 16:52:17 +0100
From:   Jeroen Hofstee <jhofstee@...tronenergy.com>
To:     Oliver Hartkopp <socketcan@...tkopp.net>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        linux-can@...r.kernel.org
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
        "moderated list:ARM/Allwinner sunXi SoC support" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] can: don't count arbitration lose as an error

Hello Oliver,

On 11/28/20 6:23 PM, Oliver Hartkopp wrote:
>
>
> On 27.11.20 12:09, Jeroen Hofstee wrote:
>> Hi,
>>
>> On 11/27/20 11:30 AM, Marc Kleine-Budde wrote:
>>> On 11/27/20 10:59 AM, Jeroen Hofstee wrote:
>>>> 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.
>>>
>>>> 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.
>>
>>
>>>   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++;
>>                  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.
>
> I have a PCAN-ExpressCard 34 here, which should make it in a test 
> setup as it acts as a PCI attached SJA1000.
>
> Will take a look at that arbitration lost behaviour on Monday. A 
> really interesting detail!
>
>

Thanks, appreciated. I would be surprised if this path is not taken though.

With kind regards,

Jeroen