Re: FlexCAN on i.MX28 interrupt flooding retrying send

[Matthias Klein]

Hello Stanislav,

I made a similar observation on an i.MX537 with the 3.12.12-rt19 kernel: 
I see the same interrupt flooed when the bus is disconnected.

What do you mean with "kills the machine"? I have a high interrupt load, 
but the machine is still responsive.


Best regards,

Matthias


------ Originalnachricht ------
Von: "Stanislav Meduna" <stano@xxxxxxxxxx>
An: wg@xxxxxxxxxxxxxx; mkl@xxxxxxxxxxxxxx; linux-can@xxxxxxxxxxxxxxx; 
"linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>; 
"linux-rt-users@xxxxxxxxxxxxxxx" <linux-rt-users@xxxxxxxxxxxxxxx>
Gesendet: 07.03.2014 09:08:42
Betreff: FlexCAN on i.MX28 interrupt flooding retrying send
> Hi,
>
> I am using a FlexCAN CAN controller on a Freescale i.MX28 platform [1].
> If a packet is being sent when the bus is disconnected, I am getting
> an interrupt flooed that basically kills the machine.
>
> This is _not_ the same problem as [2] - my kernel already has
> the fix.
>
> The first interrupt comes with ESR 0x00028652, i.e.
>
> TXWRN_INT
> BIT1_ERR
> STF_ERR
> TX_WRN
> TXRX
> FLT_CONF error passive
> ERR_INT
>
> The next ones come the same without the acked TXWRN_INT.
> Reading the ESR again immediately after acking gives
> 0x00000250, i.e.
>
> TX_WRN
> TXRX
> FLT_CONF error passive
>
> so everything ackable has actually been acked.
>
> I think that the problem is that the FlexCAN tries to retransmit
> the frame indefinitely. Each retry senses the bus in the invalid
> state (BIT1_ERR) and immediately fires a new ERR_INT. To verify
> this I aborted the transmitted frame in the error state in the
> interrupt handler
>
> #define FLEXCAN_ESR_ERR_TRANSMIT \
>  (FLEXCAN_ESR_BIT1_ERR | FLEXCAN_ESR_BIT0_ERR | FLEXCAN_ESR_ACK_ERR)
>
> if (reg_esr & FLEXCAN_ESR_ERR_TRANSMIT) {
>
>  /* In case of a transmission error the packet is retried and
>   * if the error persists, we will get another interrupt right
>   * away. Abort the transmission - a lost packet is better than
>   * an irq storm.
>   */
>  if(printk_ratelimit())
>   netdev_err(dev, "Aborted transmission, ESR %08x\n", reg_esr);
>
>  can_get_echo_skb(dev, 0);
>  flexcan_write(FLEXCAN_MB_CNT_CODE(0x4),
>   &regs->cantxfg[FLEXCAN_TX_BUF_ID].can_ctrl);
>  netif_wake_queue(dev);
> }
>
> and the problem disappeared as expected. However, the correct
> way is probably to retry during some reasonable (configurable?)
> time interval.
>
> What puzzles me is that I did not found any other instance
> of this problem in the relevant mailing lists, only the original [2].
>
> I am using the 3.4.77 kernel with the realtime patches, but the
> code in the latest mainline looks the same in this respect.
> Maybe the realtime patches change some bevaviour, but I don't
> think they affect the core problem. I am not really an expert
> in the network devices, NAPI etc - maybe in that case the error
> interrupt should be disabled and re-enabled only if the
> error condition goes away? - I don't know...
>
> Please Cc: me when answering to the list.
>
> [1] 
> http://www.tq-group.com/en/products/product-details/prod/embedded-modul-tqma28/extb/Main/productdetail/
> [2] https://gitorious.org/linux-can/wg-linux-can-next/commit/8ad94fa
>
> Thanks
> --
>                                            Stano
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