linux-kernel - Re: [PATCH] rtc: rtc-omap: Replace mdelay() with msleep() in omap_rtc_power

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Message-ID: <20180828084940.GA28861@localhost>
Date:   Tue, 28 Aug 2018 10:49:40 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Jia-Ju Bai <baijiaju1990@...il.com>, johan@...nel.org,
        j-keerthy@...com, a.zummo@...ertech.it, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: rtc-omap: Replace mdelay() with msleep() in
 omap_rtc_power_off()

On Mon, Aug 27, 2018 at 10:55:17PM +0200, Alexandre Belloni wrote:
> Hi,
> 
> On 30/07/2018 21:53:14+0800, Jia-Ju Bai wrote:
> > omap_rtc_power_off() is never called in atomic context.
> > It calls mdelay() to busily wait, which is not necessary.
> > mdelay() can be replaced with msleep().
> > 
> > This is found by a static analysis tool named DCNS written by myself.
> > 
> > Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> > ---
> >  drivers/rtc/rtc-omap.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/rtc/rtc-omap.c b/drivers/rtc/rtc-omap.c
> > index 39086398833e..ef3d09525d0f 100644
> > --- a/drivers/rtc/rtc-omap.c
> > +++ b/drivers/rtc/rtc-omap.c
> > @@ -476,7 +476,7 @@ static void omap_rtc_power_off(void)
> >  	 * power off the system. Add a 500 ms margin for external latencies
> >  	 * (e.g. debounce circuits).
> >  	 */
> > -	mdelay(2500);
> > +	msleep(2500);
> 
> I'm not sure about that one because this is a poweroff function so it
> doesn't really make sense to sleep versus busy waiting (all the drivers
> in power/reset use mdelay())

This power-off handler is called with interrupts disabled (as mentioned
in the function header) and must not sleep.

Johan