netdev - Re: [PATCH V2 1/4] can: flexcan: fix deadlock when using self wakeup

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Message-ID: <cad4be61-b409-093a-9f05-9de691bc4a10@pengutronix.de>
Date:   Tue, 3 Dec 2019 18:42:16 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Joakim Zhang <qiangqing.zhang@....com>,
        "sean@...nix.com" <sean@...nix.com>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>
Cc:     dl-linux-imx <linux-imx@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH V2 1/4] can: flexcan: fix deadlock when using self wakeup

On 12/3/19 6:25 PM, Marc Kleine-Budde wrote:
> On 11/27/19 6:56 AM, Joakim Zhang wrote:
>> From: Sean Nyekjaer <sean@...nix.com>
>>
>> When suspending, when there is still can traffic on the interfaces the
>> flexcan immediately wakes the platform again. As it should :-). But it
>> throws this error msg:
>> [ 3169.378661] PM: noirq suspend of devices failed
>>
>> On the way down to suspend the interface that throws the error message does
>> call flexcan_suspend but fails to call flexcan_noirq_suspend. That means the
>> flexcan_enter_stop_mode is called, but on the way out of suspend the driver
>> only calls flexcan_resume and skips flexcan_noirq_resume, thus it doesn't call
>> flexcan_exit_stop_mode. This leaves the flexcan in stop mode, and with the
>> current driver it can't recover from this even with a soft reboot, it requires
>> a hard reboot.
>>
>> This patch can fix deadlock when using self wakeup, it happenes to be
>> able to fix another issue that frames out-of-order in first IRQ handler
>> run after wakeup.
>>
>> In wakeup case, after system resume, frames received out-of-order in
>> first IRQ handler, the problem is wakeup latency from frame reception to
>> IRQ handler is much bigger than the counter overflow. This means it's
>> impossible to sort the CAN frames by timestamp. The reason is that controller
>> exits stop mode during noirq resume, then it can receive the frame immediately.
>> If noirq reusme stage consumes much time, it will extend interrupt response
>> time. So exit stop mode during resume stage instead of noirq resume can
>> fix this issue.
>>
>> Fixes: de3578c198c6 ("can: flexcan: add self wakeup support")
>> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
>> Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
>> ------
>> ChangeLog:
>> 	V1->V2: no change.
>> ---
>>  drivers/net/can/flexcan.c | 19 +++++++++++--------
>>  1 file changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c
>> index 2efa06119f68..2297663cacb2 100644
>> --- a/drivers/net/can/flexcan.c
>> +++ b/drivers/net/can/flexcan.c
>> @@ -134,8 +134,7 @@
>>  	(FLEXCAN_ESR_ERR_BUS | FLEXCAN_ESR_ERR_STATE)
>>  #define FLEXCAN_ESR_ALL_INT \
>>  	(FLEXCAN_ESR_TWRN_INT | FLEXCAN_ESR_RWRN_INT | \
>> -	 FLEXCAN_ESR_BOFF_INT | FLEXCAN_ESR_ERR_INT | \
>> -	 FLEXCAN_ESR_WAK_INT)
>> +	 FLEXCAN_ESR_BOFF_INT | FLEXCAN_ESR_ERR_INT)
> 
> Why do you remove the FLEXCAN_ESR_WAK_INT from the FLEXCAN_ESR_ALL_INT?
> 
>>  
>>  /* FLEXCAN interrupt flag register (IFLAG) bits */
>>  /* Errata ERR005829 step7: Reserve first valid MB */
>> @@ -960,6 +959,12 @@ static irqreturn_t flexcan_irq(int irq, void *dev_id)
>>  
>>  	reg_esr = priv->read(&regs->esr);
>>  
>> +	/* ACK wakeup interrupt */
>> +	if (reg_esr & FLEXCAN_ESR_WAK_INT) {
>> +		handled = IRQ_HANDLED;
>> +		priv->write(reg_esr & FLEXCAN_ESR_WAK_INT, &regs->esr);
>> +	}
>> +
> 
> If FLEXCAN_ESR_WAK_INT stays in FLEXCAN_ESR_ALL_INT, you don't need that
> explicit ACK here.

Otherwise this patch is OK. With this patch the flexcan_suspend() and
flexcan_resume() look finally symmetric. \o/

Marc

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



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