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

From: Ken Sloat
Date: Fri Jun 14 2019 - 16:50:21 EST

> -----Original Message-----
> From: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
> Sent: Friday, June 14, 2019 4:33 PM
> To: Ken Sloat <KSloat@xxxxxxxxxxxxxx>
> Cc: Guenter Roeck <linux@xxxxxxxxxxxx>; nicolas.ferre@xxxxxxxxxxxxx;
> ludovic.desroches@xxxxxxxxxxxxx; wim@xxxxxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; linux-watchdog@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> 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

Ken Sloat