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From:   Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
To:     Marco Felsch <m.felsch@pengutronix.de>,
        Support Opensource <Support.Opensource@diasemi.com>,
        "linux@roeck-us.net" <linux@roeck-us.net>,
        Steve Twiss <stwiss.opensource@diasemi.com>,
        Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
CC:     "linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>
Subject: RE: [PATCH] watchdog: da9062: do not ping the hw during stop()
Thread-Topic: [PATCH] watchdog: da9062: do not ping the hw during stop()
Thread-Index: AQHVz3J0N/2psq1VGU68MqLs/CX6Pqf/54WA
Date:   Tue, 28 Jan 2020 10:13:33 +0000
Message-ID: <AM6PR10MB2263D6F62A45568D5671377D800A0@AM6PR10MB2263.EURPRD10.PROD.OUTLOOK.COM>
References: <20200120091729.16256-1-m.felsch@pengutronix.de>
In-Reply-To: <20200120091729.16256-1-m.felsch@pengutronix.de>
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On 20 January 2020 09:17, Marco Felsch wrote:

> The da9062 hw has a minimum ping cool down phase of at least 200ms. The
> driver takes that into account by setting the min_hw_heartbeat_ms to
> 300ms and the core guarantees that the hw limit is observed for the
> ping() calls. But the core can't guarantees the required minimum ping
> cool down phase if a stop() command is send immediately after the ping()
> command. So it is not allowed to ping the watchdog within the stop()
> command as the driver do. Remove the ping can be done without doubts
> because the watchdog gets disabled anyway and a (re)start reset the
> watchdog counter too.
>=20

Good spot. Thanks for this. Am wondering if this might also be an issue for
da9062_wdt_set_timeout() which calls down to
da9062_wdt_update_timeout_register() which in turn pings the watchdog first
before disabling it and then setting the new timeout value. I think it make=
s
sense to remove the ping from da9062_wdt_update_timeout_register() as well =
to
avoid any possible issues where a ping() is called and then immediately aft=
er
there's a call to adjust the timeout. If you can double check my hypothesis
that would be good though.

> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
>  drivers/watchdog/da9062_wdt.c | 7 -------
>  1 file changed, 7 deletions(-)
>=20
> diff --git a/drivers/watchdog/da9062_wdt.c b/drivers/watchdog/da9062_wdt.=
c
> index 77b6b5336067..0ad15d55071c 100644
> --- a/drivers/watchdog/da9062_wdt.c
> +++ b/drivers/watchdog/da9062_wdt.c
> @@ -97,13 +97,6 @@ static int da9062_wdt_stop(struct watchdog_device *wdd=
)
>  	struct da9062_watchdog *wdt =3D watchdog_get_drvdata(wdd);
>  	int ret;
>=20
> -	ret =3D da9062_reset_watchdog_timer(wdt);
> -	if (ret) {
> -		dev_err(wdt->hw->dev, "Failed to ping the watchdog (err =3D
> %d)\n",
> -			ret);
> -		return ret;
> -	}
> -
>  	ret =3D regmap_update_bits(wdt->hw->regmap,
>  				 DA9062AA_CONTROL_D,
>  				 DA9062AA_TWDSCALE_MASK,
> --
> 2.20.1