Re: FlexCAN on i.MX28 interrupt flooding retrying send

[Marc Kleine-Budde <mkl@pengutronix.de>]

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Adding the linux-can mailinglist to Cc.

Marc

On 03/07/2014 09:08 AM, Stanislav Meduna wrote:
> 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
> 


-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |


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