netdev - RE: [PATCH 1/3] can: flexcan: fix deadlock when using self wakeup

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Message-ID: <DB7PR04MB461895F57FD4F360A723D2FAE64D0@DB7PR04MB4618.eurprd04.prod.outlook.com>
Date:   Mon, 18 Nov 2019 08:04:39 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Sean Nyekjaer <sean@...nix.com>,
        "mkl@...gutronix.de" <mkl@...gutronix.de>
CC:     "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 1/3] can: flexcan: fix deadlock when using self wakeup


> -----Original Message-----
> From: Sean Nyekjaer <sean@...nix.com>
> Sent: 2019年11月18日 15:53
> To: Joakim Zhang <qiangqing.zhang@....com>; mkl@...gutronix.de
> Cc: linux-can@...r.kernel.org; dl-linux-imx <linux-imx@....com>;
> netdev@...r.kernel.org
> Subject: Re: [PATCH 1/3] can: flexcan: fix deadlock when using self wakeup
> 
> 
> 
> On 18/11/2019 08.05, Joakim Zhang wrote:
> >
> >> -----Original Message-----
> >> From: linux-can-owner@...r.kernel.org
> >> <linux-can-owner@...r.kernel.org> On Behalf Of Sean Nyekjaer
> >> Sent: 2019年11月15日 17:08
> >> To: Joakim Zhang <qiangqing.zhang@....com>; mkl@...gutronix.de
> >> Cc: linux-can@...r.kernel.org; dl-linux-imx <linux-imx@....com>;
> >> netdev@...r.kernel.org
> >> Subject: Re: [PATCH 1/3] can: flexcan: fix deadlock when using self
> >> wakeup
> >>
> >>
> >>
> >> On 15/11/2019 06.03, 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,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.
> >>>
> >>> Fixes: de3578c198c6 ("can: flexcan: add self wakeup support")
> >>> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> >>> Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> >>
> >> Hi Joakim and Marc
> >>
> >> We have quite a few devices in the field where flexcan is stuck in Stop-Mode.
> >> We do not have the possibility to cold reboot them, and hot reboot
> >> will not get flexcan out of stop-mode.
> >> So flexcan comes up with:
> >> [  279.444077] flexcan: probe of 2090000.flexcan failed with error
> >> -110 [  279.501405] flexcan: probe of 2094000.flexcan failed with
> >> error -110
> >>
> >> They are on, de3578c198c6 ("can: flexcan: add self wakeup support")
> >>
> >> Would it be a solution to add a check in the probe function to pull
> >> it out of stop-mode?
> >
> > Hi Sean,
> >
> > Soft reset cannot be applied when clocks are shut down in a low power mode.
> The module should be first removed from low power mode, and then soft reset
> can be applied.
> > And exit from stop mode happens when the Stop mode request is removed,
> or when activity is detected on the CAN bus and the Self Wake Up mechanism is
> enabled.
> >
> > So from my point of view, we can add a check in the probe function to
> > pull it out of stop mode, since controller actually could be stuck in stop mode
> if suspend/resume failed and users just want a warm reset for the system.
> 
> Exactly what I thought could be done :)
> 
> >
> > Could you please tell me how can I generate a warm reset? AFAIK, both
> "reboot" command put into prompt and RST KEY in our EVK board all play a role
> of cold reset.
> 
> Warm reset is just `reboot` :-) Cold is poweroff...

I add the code flexcan_enter_stop_mode(priv) at the end of the probe function, 'reboot' the system directly after system active.
However, I do not meet the probe error, it can probe successfully. Do you know the reason?

Best Regards,
Joakim Zhang
> /Sean
> 
> >
> > Best Regards,
> > Joakim Zhang
> >> /Sean