netdev - Re: [PATCH] can: flexcan: fix deadlock when using self wakeup

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Date:   Fri, 17 May 2019 19:18:43 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Joakim Zhang <qiangqing.zhang@....com>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>
Cc:     dl-linux-imx <linux-imx@....com>,
        "wg@...ndegger.com" <wg@...ndegger.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Aisheng Dong <aisheng.dong@....com>
Subject: Re: [PATCH] can: flexcan: fix deadlock when using self wakeup

On 5/17/19 4:39 AM, Joakim Zhang wrote:
> As reproted by Sean Nyekjaer bellow:
> 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.
> 
> Fixes: de3578c198c6 ("can: flexcan: add self wakeup support")
> 
> This patch intends to fix the issue, and also add comment to explain the
> wakeup flow.
> 
> Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>

The existing self wakeup support:

| de3578c198c6 ("can: flexcan: add self wakeup support")

looks broken to me.

According to the data sheet:

> To enter stop mode, the CPU should manually assert a global Stop Mode
> request (see the CAN1_STOP_REQ and CAN2_STOP_REQ bit in the register
> IOMUXC_GPR4) and check the acknowledgement asserted by the FlexCAN
> (see the CAN1_STOP_ACK and CAN2_STOP_ACK in the register
> IOMUXC_GPR4). The CPU must only consider the FlexCAN in Stop Mode
> when both request and acknowledgement conditions are satisfied.
you have to poll for the acknowledgement, which is not done in the
driver. Please fix that first.

As far as I understand the documentation the suspend() and resume
functions should be symmetric. If they are, you shouldn't need the
in_stop_mode hack.

regards,
Marc

-- 
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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