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

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Date:   Tue, 11 Jun 2019 06:55:53 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>,
        "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


> -----Original Message-----
> From: Marc Kleine-Budde <mkl@...gutronix.de>
> Sent: 2019年5月18日 1:19
> To: Joakim Zhang <qiangqing.zhang@....com>; linux-can@...r.kernel.org
> Cc: dl-linux-imx <linux-imx@....com>; wg@...ndegger.com;
> 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.

Hi Marc,

  Patch has sent out to fix it. Thank you!

> 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.

  Yes, we don't need in_stop_mode hack if we can let FlexCAN stop mode mechanism be symmetric
in suspend() and resume(). However, it can't be realized as I explained in the patch.
  Ang suggestion can provide?
 
Best Regards,
Joakim Zhang

> regards,
> Marc
> 
> --
> Pengutronix e.K.                  | Marc Kleine-Budde           |
> Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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