linux-kernel - Re: [PATCH v2] watchdog: omap_wdt: Add 'early

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Message-ID: <1411469087.32524.6.camel@lp-lvrv.comap.cz>
Date:	Tue, 23 Sep 2014 12:44:47 +0200
From:	Rostislav Lisovy <lisovy@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Wim Van Sebroeck <wim@...ana.be>, linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org, sojkam1@....cvut.cz,
	michal.vokac@...ap.cz, Rostislav Lisovy <lisovy@...ica.cz>
Subject: Re: [PATCH v2] watchdog: omap_wdt: Add 'early_disable' module
 parameter

On Čt, 2014-09-18 at 21:12 -0700, Guenter Roeck wrote:
> How about reading the OMAP_WATCHDOG_SPR register ?

Unfortunately this would be not only extremely fragile (someone writes
correct start sequence followed by some garbage -- WD is running and we
are reading garbage) but according to some experiments seems not to work
at all (I am reading "0" even for a running WD probably as a result to
the pm_runtime_get_sync() call).

One of the TI employees on the TI forum confirmed (I know this is not a
rock-solid information) that it is not possible to safely determine if
the WD is running or not.

> Either case, you can not issue a message about the watchdog being
> stopped or started if you don't know if it was actually stopped
> or started. Also, if you don't really know if the watchdog was
> stopped or started, all you can do is to either stop or start it,
> without judgment about its previous condition.

You are right. I was blinded by our use case where the watchdog is
always started by the bootloader.
I will wait to see if the WATCHDOG_KEEP_ON will be integrated and then I
will add the feature for the omap_wdt.

Best regards;
Rostislav

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