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

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Date:   Fri, 27 Nov 2020 12:09:54 +0100
From:   Jeroen Hofstee <jhofstee@...tronenergy.com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>, linux-can@...r.kernel.org
Cc:     Oliver Hartkopp <socketcan@...tkopp.net>,
        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

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.

>
>> Signed-off-by: Jeroen Hofstee <jhofstee@...tronenergy.com>
> I've split this into two patches, and added Fixes: lines, and pushed this for
> now to linux-can/sja1000.
>
Thanks, regards,

Jeroen