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

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Message-ID: <20190614203327.GE3369@piout.net>
Date:   Fri, 14 Jun 2019 22:33:27 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Ken Sloat <KSloat@...pglobal.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

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.

> 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.

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