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

[Alice Guo (OSS)]

> -----Original Message-----
> From: Marco Felsch <m.felsch at pengutronix.de>
> Sent: Tuesday, August 16, 2022 2:24 PM
> To: Alice Guo (OSS) <alice.guo at oss.nxp.com>
> Cc: wim at linux-watchdog.org; linux at roeck-us.net; shawnguo at kernel.org;
> s.hauer at pengutronix.de; festevam at gmail.com;
> linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org;
> dl-linux-imx <linux-imx at nxp.com>; kernel at pengutronix.de;
> linux-watchdog at vger.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 at nxp.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 at nxp.com>
> > Signed-off-by: Jacky Bai <ping.bai at nxp.com>
> > Signed-off-by: Alice Guo <alice.guo at nxp.com>
> > Reviewed-by: Ye Li <ye.li at 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 = imx7ulp_wdt_wait(base, WDOG_CS_ULK);
> >  	if (ret)
> >  		goto init_out;
> > --
> > 2.17.1
> >
> >
> >