linux-kernel - RE: [PATCH v2 1/1] watchdog: atmel: atmel-sama5d4-wdt: Disable watchdog on system suspend

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Date:   Fri, 14 Jun 2019 20:45:28 +0000
From:   Ken Sloat <KSloat@...pglobal.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
CC:     Guenter Roeck <linux@...ck-us.net>,
        "nicolas.ferre@...rochip.com" <nicolas.ferre@...rochip.com>,
        "ludovic.desroches@...rochip.com" <ludovic.desroches@...rochip.com>,
        "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 1/1] watchdog: atmel: atmel-sama5d4-wdt: Disable
 watchdog on system suspend

> -----Original Message-----
> From: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Sent: Friday, June 14, 2019 4:33 PM
> To: Ken Sloat <KSloat@...pglobal.com>
> Cc: Guenter Roeck <linux@...ck-us.net>; nicolas.ferre@...rochip.com;
> ludovic.desroches@...rochip.com; wim@...ux-watchdog.org; linux-arm-
> kernel@...ts.infradead.org; linux-watchdog@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH v2 1/1] watchdog: atmel: atmel-sama5d4-wdt: Disable
> watchdog on system suspend
> 
> [This is an EXTERNAL EMAIL]
> ________________________________
> 
> On 14/06/2019 18:43:22+0000, Ken Sloat wrote:
> > Well I'm a little confused still because there are two separate
> > comments in these statements. The first within resume implies that the
> > init should be called because we might have lost register values for
> > some reason unexplained.
> 
> The sama5d2 has a suspend mode where power to the core is completely
> cut. Only a few IPs remain powered (in the backup power domain).
> Unfortunately, the watchdog is not in that domain and may lose its registers.
> 
> > Then within the init it says that the bootloader might have modified
> > the registers so we should check them and then update it or otherwise
> > disable it. I'm not trying to pick apart the logic or anything, I'm
> > just readily assuming it is good as it was already reviewed before.
> >
> 
> The bootloaders may have started the watchdog (this makes sense if you
> really care about reliability) and so we need to be careful to keep the proper
> parameters.

Thanks for the explanation Alexandre I appreciate it.

> > So without digging into that too much, if we don't know if any of the
> > runtime situations above might have occurred, then isn't it best to
> > leave my patch as is? Yes this has the side effect of resetting the
> > timer count, but if the init call is needed and we don't have any way
> > to know if any of the situations occurred, then we have no choice right?
> >
> 
> Until we can differentiate between suspend modes, we have no other
> choice.

Ok I will leave my patch as is for now then

> --
> Alexandre Belloni, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

Thanks,
Ken Sloat