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

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Message-ID: <b77829d5-9eda-a244-3ee8-2ccdbdfb6524@pengutronix.de>
Date:   Tue, 3 Dec 2019 18:25:08 +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 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.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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