linux-kernel - RE: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for unlock sequence

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Message-ID: <AM6PR04MB60537292F559EC012F0EB510E2719@AM6PR04MB6053.eurprd04.prod.outlook.com>
Date:   Mon, 22 Aug 2022 07:49:20 +0000
From:   "Alice Guo (OSS)" <alice.guo@....nxp.com>
To:     Marco Felsch <m.felsch@...gutronix.de>
CC:     "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>
Subject: RE: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for
 unlock sequence

> -----Original Message-----
> From: Marco Felsch <m.felsch@...gutronix.de>
> Sent: Tuesday, August 16, 2022 2:24 PM
> To: Alice Guo (OSS) <alice.guo@....nxp.com>
> Cc: wim@...ux-watchdog.org; linux@...ck-us.net; shawnguo@...nel.org;
> s.hauer@...gutronix.de; festevam@...il.com;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> dl-linux-imx <linux-imx@....com>; kernel@...gutronix.de;
> linux-watchdog@...r.kernel.org
> Subject: Re: [PATCH 2/7] watchdog: imx7ulp: Add explict memory barrier for
> unlock sequence
> 
> On 22-08-16, Alice Guo (OSS) wrote:
> > From: Jacky Bai <ping.bai@....com>
> >
> > Add explict memory barrier for the wdog unlock sequence.
> 
> Did you inspected any failures? It's not enough to say what you did, you need
> to specify the why as well.
> 
> Regards,
>   Marco

Hi,

Two 16-bit writes of unlocking the Watchdog should be completed within a certain 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 affected by subsequent instructions. The reason will be added in the commit log of v2.

Best Regards,
Alice Guo

> 
> >
> > Suggested-by: Ye Li <ye.li@....com>
> > Signed-off-by: Jacky Bai <ping.bai@....com>
> > Signed-off-by: Alice Guo <alice.guo@....com>
> > Reviewed-by: Ye Li <ye.li@....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 = imx7ulp_wdt_wait(base, WDOG_CS_ULK);
> >  	if (ret)
> >  		goto init_out;
> > --
> > 2.17.1
> >
> >
> >