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

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Message-ID: <20190615142216.GA32514@roeck-us.net>
Date:   Sat, 15 Jun 2019 07:22:16 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Ken Sloat <KSloat@...pglobal.com>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "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

On Fri, Jun 14, 2019 at 08:45:28PM +0000, Ken Sloat wrote:
> > -----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
> 

If that is what those involved in this discussion argue for, they will
need to confirm with Reviewed-by: or Acked-by: tags.

Thanks,
Guenter

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