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From:   "Alice Guo (OSS)" <alice.guo@oss.nxp.com>
To:     Marco Felsch <m.felsch@pengutronix.de>
CC:     "wim@linux-watchdog.org" <wim@linux-watchdog.org>,
        "linux@roeck-us.net" <linux@roeck-us.net>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
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        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        "linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>
Subject: RE: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for
 unlock sequence
Thread-Topic: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for
 unlock sequence
Thread-Index: AQHYsSoBdxZHPlON40a5XuD6jrx4qK2xDxMAgAl1k+A=
Date:   Mon, 22 Aug 2022 07:49:20 +0000
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References: <20220816043643.26569-1-alice.guo@oss.nxp.com>
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> -----Original Message-----
> From: Marco Felsch <m.felsch@pengutronix.de>
> Sent: Tuesday, August 16, 2022 2:24 PM
> To: Alice Guo (OSS) <alice.guo@oss.nxp.com>
> Cc: wim@linux-watchdog.org; linux@roeck-us.net; shawnguo@kernel.org;
> s.hauer@pengutronix.de; festevam@gmail.com;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> dl-linux-imx <linux-imx@nxp.com>; kernel@pengutronix.de;
> linux-watchdog@vger.kernel.org
> Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier fo=
r
> unlock sequence
>=20
> On 22-08-16, Alice Guo (OSS) wrote:
> > From: Jacky Bai <ping.bai@nxp.com>
> >
> > Add explict memory barrier for the wdog unlock sequence.
>=20
> Did you inspected any failures? It's not enough to say what you did, you =
need
> to specify the why as well.
>=20
> Regards,
>   Marco

Hi,

Two 16-bit writes of unlocking the Watchdog should be completed within a ce=
rtain time. The first mb() is used to ensure that previous instructions are=
 completed.
The second mb() is used to ensure that the unlock sequence cannot be affect=
ed by subsequent instructions. The reason will be added in the commit log o=
f v2.

Best Regards,
Alice Guo

>=20
> >
> > Suggested-by: Ye Li <ye.li@nxp.com>
> > Signed-off-by: Jacky Bai <ping.bai@nxp.com>
> > Signed-off-by: Alice Guo <alice.guo@nxp.com>
> > Reviewed-by: Ye Li <ye.li@nxp.com>
> > ---
> >  drivers/watchdog/imx7ulp_wdt.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/watchdog/imx7ulp_wdt.c
> > b/drivers/watchdog/imx7ulp_wdt.c index 014f497ea0dc..b8ac0cb04d2f
> > 100644
> > --- a/drivers/watchdog/imx7ulp_wdt.c
> > +++ b/drivers/watchdog/imx7ulp_wdt.c
> > @@ -179,9 +179,13 @@ static int imx7ulp_wdt_init(void __iomem *base,
> unsigned int timeout)
> >  	int ret;
> >
> >  	local_irq_disable();
> > +
> > +	mb();
> >  	/* unlock the wdog for reconfiguration */
> >  	writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
> >  	writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
> > +	mb();
> > +
> >  	ret =3D imx7ulp_wdt_wait(base, WDOG_CS_ULK);
> >  	if (ret)
> >  		goto init_out;
> > --
> > 2.17.1
> >
> >
> >