linux-kernel - Re: FlexCAN on i.MX28 interrupt flooding retrying send

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Message-Id: <emb03a570d-a7ce-4ae7-b026-29c159b98a36@nb-mak>
Date:	Fri, 07 Mar 2014 08:32:57 +0000
From:	"Matthias Klein" <matthias.klein@...imeas.de>
To:	"Stanislav Meduna" <stano@...una.org>, wg@...ndegger.com,
	mkl@...gutronix.de, linux-can@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>
Subject: Re: FlexCAN on i.MX28 interrupt flooding retrying send

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@...una.org>
An: wg@...ndegger.com; mkl@...gutronix.de; linux-can@...r.kernel.org; 
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>; 
"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>
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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>

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