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

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Date:   Wed, 27 Nov 2019 10:58:06 +0100
From:   Sean Nyekjaer <sean@...nix.com>
To:     Joakim Zhang <qiangqing.zhang@....com>,
        "mkl@...gutronix.de" <mkl@...gutronix.de>,
        "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 27/11/2019 06.56, 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>
Tested-by: Sean Nyekjaer <sean@...nix.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)
>   
>   /* 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);
> +	}
> +
>   	/* ACK all bus error and state change IRQ sources */
>   	if (reg_esr & FLEXCAN_ESR_ALL_INT) {
>   		handled = IRQ_HANDLED;
> @@ -1722,6 +1727,9 @@ static int __maybe_unused flexcan_resume(struct device *device)
>   		netif_start_queue(dev);
>   		if (device_may_wakeup(device)) {
>   			disable_irq_wake(dev->irq);
> +			err = flexcan_exit_stop_mode(priv);
> +			if (err)
> +				return err;
>   		} else {
>   			err = pm_runtime_force_resume(device);
>   			if (err)
> @@ -1767,14 +1775,9 @@ static int __maybe_unused flexcan_noirq_resume(struct device *device)
>   {
>   	struct net_device *dev = dev_get_drvdata(device);
>   	struct flexcan_priv *priv = netdev_priv(dev);
> -	int err;
>   
> -	if (netif_running(dev) && device_may_wakeup(device)) {
> +	if (netif_running(dev) && device_may_wakeup(device))
>   		flexcan_enable_wakeup_irq(priv, false);
> -		err = flexcan_exit_stop_mode(priv);
> -		if (err)
> -			return err;
> -	}
>   
>   	return 0;
>   }
>