Message-ID: <dd8f5269-8403-702b-b054-e031423ffc73@geanix.com>
Date:   Tue, 20 Aug 2019 12:25:24 +0200
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:     "wg@...ndegger.com" <wg@...ndegger.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        Martin Hundebøll <martin@...nix.com>
Subject: Re: [PATCH REPOST 1/2] can: flexcan: fix deadlock when using self
 wakeup



On 16/08/2019 10.20, Joakim Zhang wrote:
> As reproted by Sean Nyekjaer below:
> 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.
> 
> The best way to exit stop mode is in Wake Up interrupt context, and then
> suspend() and resume() functions can be symmetric. However, stop mode
> request and ack will be controlled by SCU(System Control Unit) firmware(manage
> clock,power,stop mode, etc. by Cortex-M4 core) in coming i.MX8(QM/QXP). And SCU
> firmware interface can't be available in interrupt context.
> 
> For compatibillity, the wake up mechanism can't be symmetric, so we need
> in_stop_mode hack.
> 
> Fixes: de3578c198c6 ("can: flexcan: add self wakeup support")
> Reported-by: Sean Nyekjaer <sean@...nix.com>
> Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> 

Unfortunatly it's still possible to reproduce the deadlock with this 
patch...

[  689.921717] flexcan: probe of 2094000.flexcan failed with error -110

My test setup:
PC with CAN-USB dongle connected to can0 and can1.

PC:
$ while true; do cansend can0 '123#DEADBEEF'; done

iMX6ull:
root@...26:~# systemctl suspend 
 

[  365.858054] systemd[1]: Reached target Sleep.
root@...26:~# [  365.939826] systemd[1]: Starting Suspend...
[  366.115839] systemd-sleep[248]: Suspending system...
[  366.517949] dpm_run_callback(): platform_pm_suspend+0x0/0x5c returns -110
[  366.518249] PM: Device 2094000.flexcan failed to suspend: error -110
[  366.518406] PM: Some devices failed to suspend, or early wake event 
detected
[  366.732162] dpm_run_callback(): platform_pm_suspend+0x0/0x5c returns -110
[  366.732285] PM: Device 2090000.flexcan failed to suspend: error -110
[  366.732330] PM: Some devices failed to suspend, or early wake event 
detected
[  366.890637] systemd-sleep[248]: System resumed.
[  366.923062] systemd[1]: Started Suspend.
[  366.942819] systemd[1]: sleep.target: Unit not needed anymore. Stopping.
[  366.954791] systemd[1]: Stopped target Sleep.
[  366.962402] systemd[1]: Reached target Suspend.
[  366.977546] systemd-logind[135]: Operation 'sleep' finished.
[  366.979194] systemd[1]: suspend.target: Unit not needed anymore. 
Stopping.
[  366.993831] systemd[1]: Stopped target Suspend.
[  367.139972] systemd-networkd[220]: usb0: Lost carrier
[  367.294077] systemd-networkd[220]: usb0: Gained carrier

root@...26:~# candump can0 | head -n 2 

   can0  123   [4]  DE AD BE EF
   can0  123   [4]  DE AD BE EF
root@...26:~# candump can1 | head -n 2 

   can1  123   [4]  DE AD BE EF
   can1  123   [4]  DE AD BE EF
root@...26:~# systemctl suspend 

root@...26:~# [  385.106658] systemd[1]: Reached target Sleep.
[  385.147602] systemd[1]: Starting Suspend...
[  385.246421] systemd-sleep[260]: Suspending system...
[  385.634733] dpm_run_callback(): platform_pm_suspend+0x0/0x5c returns -110
[  385.634855] PM: Device 2090000.flexcan failed to suspend: error -110
[  385.634897] PM: Some devices failed to suspend, or early wake event 
detected
[  385.856251] PM: noirq suspend of devices failed
[  385.998364] systemd-sleep[260]: System resumed.
[  386.023390] systemd[1]: Started Suspend.
[  386.031570] systemd[1]: sleep.target: Unit not needed anymore. Stopping.
[  386.055886] systemd[1]: Stopped target Sleep.
[  386.061430] systemd[1]: Reached target Suspend.
[  386.066142] systemd[1]: suspend.target: Unit not needed anymore. 
Stopping.
[  386.112575] systemd-networkd[220]: usb0: Lost carrier
[  386.116797] systemd-logind[135]: Operation 'sleep' finished.
[  386.146161] systemd[1]: Stopped target Suspend.
[  386.260866] systemd-networkd[220]: usb0: Gained carrier
root@...26:~# candump can0 | head -n 2
   can0  123   [4]  DE AD BE EF
   can0  123   [4]  DE AD BE EF
root@...26:~# candump can1 | head -n 2 

   can1  123   [4]  DE AD BE EF
   can1  123   [4]  DE AD BE EF
root@...26:~# systemctl suspend 

[  396.919303] systemd[1]: Reached target Sleep.
root@...26:~# [  396.964722] systemd[1]: Starting Suspend...
[  397.067336] systemd-sleep[268]: Suspending system...
[  397.574571] PM: noirq suspend of devices failed
[  397.834731] PM: noirq suspend of devices failed
[  397.807996] systemd-networkd[220]: usb0: Lost carrier
[  398.156295] dpm_run_callback(): platform_pm_suspend+0x0/0x5c returns -110
[  398.156339] PM: Device 2094000.flexcan failed to suspend: error -110
[  398.156509] PM: Some devices failed to suspend, or early wake event 
detected
[  398.053555] systemd-sleep[268]: Failed to write /sys/power/state: 
Device or resource busy
[  398.074751] systemd[1]: systemd-suspend.service: Main process exited, 
code=exited, status=1/FAILURE
[  398.076779] systemd[1]: systemd-suspend.service: Failed with result 
'exit-code'.
[  398.109255] systemd[1]: Failed to start Suspend.
[  398.118704] systemd[1]: Dependency failed for Suspend.
[  398.136283] systemd-logind[135]: Operation 'sleep' finished.
[  398.137770] systemd[1]: suspend.target: Job suspend.target/start 
failed with result 'dependency'.
[  398.139105] systemd[1]: sleep.target: Unit not needed anymore. Stopping.
[  398.167590] systemd[1]: Stopped target Sleep.
[  398.201558] systemd-networkd[220]: usb0: Gained carrier

root@...26:~# candump can0 | head -n 2
   can0  123   [4]  DE AD BE EF
   can0  123   [4]  DE AD BE EF
root@...26:~# candump can1 | head -n 2

nothing on can1 anymore :-(

root@...26:~# rmmod flexcan
[  622.884746] systemd-networkd[220]: can1: Lost carrier
[  623.046766] systemd-networkd[220]: can0: Lost carrier
root@...26:~# insmod /mnt/flexcan.ko
[  628.323981] flexcan 2094000.flexcan: registering netdev failed

and can1 fails to register with:
[  628.347485] flexcan: probe of 2094000.flexcan failed with error -110

/Sean

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