Re: [RFC PATCH 0/1] Suspending i.MX watchdog in WAIT mode

From: Guenter Roeck <linux@roeck-us.net>
To: Andrej Picej <andrej.picej@norik.com>, linux-watchdog@vger.kernel.org
Cc: wim@linux-watchdog.org, shawnguo@kernel.org,
	s.hauer@pengutronix.de, kernel@pengutronix.de,
	festevam@gmail.com, linux-imx@nxp.com
Subject: Re: [RFC PATCH 0/1] Suspending i.MX watchdog in WAIT mode
Date: Wed, 21 Sep 2022 07:18:43 -0700	[thread overview]
Message-ID: <5823717b-0288-a679-824d-5a26dec5a606@roeck-us.net> (raw)
In-Reply-To: <20220921124647.1521667-1-andrej.picej@norik.com>

On 9/21/22 05:46, Andrej Picej wrote:
> Hi all,
> 
> we are using i.MX6UL with its watchdog WDOG1 and kernel 5.15.62. It was
> discovered that the watchdog triggers reset when the device is put into
> 'Suspend-To-Idle' (WAIT) state.
> 

Is that equivalent to "suspend" from Linux perspective, or some other
mode ? How does the device get into this state ?

Guenter

> i.MX6UL watchdog has a WDW (Watchdog Disable for Wait) bit in WCR
> (Watchdog Control Register) which can put the watchdog in suspend when
> the device is put to WAIT mode. Similarly, WDZST bit is already set in
> imx2_wdt driver by default, which suspends the watchdog in STOP and DOZE
> modes.
> 
> This RFC patch suspends watchdog when the device is in WAIT mode, which
> fixes our problem. During development, we noticed some reports where
> setting WDW bit caused inconsistent timeout events or inability of
> watchdog to reset the board. We didn't have these problems but I am
> curious if there is a case where device is put into WAIT mode and
> watchdog should be enabled?
> 
> Maybe for cases where watchdog is used for WAIT mode supervision? So
> basically to reset the system if device doesn't exit WAIT mode on its
> own?
> 
> The problem can be recreated with:
> 
> 	imx6ul-dev:~# echo freeze > /sys/power/state
> 	[  101.093336] PM: suspend entry (s2idle)
> 	[  101.097785] Filesystems sync: 0.000 seconds
> 	[  101.122295] Freezing user space processes ... (elapsed 0.001 seconds) done.
> 	[  101.130637] OOM killer disabled.
> 	[  101.133998] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
> 	[  101.142941] printk: Suspending console(s) (use no_console_suspend to debug)
> 	...
> Device resets after watchdog timeout expires! ~105s
> 
> Thank you for your feedback.
> 
> Best regards,
> Andrej
> 
> Andrej Picej (1):
>    watchdog: imx2_wdg: suspend watchdog in WAIT mode
> 
>   drivers/watchdog/imx2_wdt.c | 3 +++
>   1 file changed, 3 insertions(+)
> 