[rtc-linux] [PATCH v3] rtc: snvs: add Freescale rtc-snvs driver

[Shawn Guo]

Thanks for looking at the patch, Andrew.

On Tue, Aug 14, 2012 at 05:03:00PM -0700, Andrew Morton wrote:
> On Fri, 13 Jul 2012 15:31:03 +0800
> Shawn Guo <shawn.guo at linaro.org> wrote:
> 
> > +static int snvs_rtc_enable(struct snvs_rtc_data *data, bool enable)
> > +{
> > +	unsigned long timeout = jiffies + msecs_to_jiffies(1);
> > +	unsigned long flags;
> > +	u32 lpcr;
> > +
> > +	spin_lock_irqsave(&data->lock, flags);
> > +
> > +	lpcr = readl(data->ioaddr + SNVS_LPCR);
> > +	if (enable)
> > +		lpcr |= SNVS_LPCR_SRTC_ENV;
> > +	else
> > +		lpcr &= ~SNVS_LPCR_SRTC_ENV;
> > +	writel(lpcr, data->ioaddr + SNVS_LPCR);
> > +
> > +	spin_unlock_irqrestore(&data->lock, flags);
> > +
> > +	while (1) {
> > +		lpcr = readl(data->ioaddr + SNVS_LPCR);
> > +
> > +		if (enable) {
> > +			if (lpcr & SNVS_LPCR_SRTC_ENV)
> > +				break;
> > +		} else {
> > +			if (!(lpcr & SNVS_LPCR_SRTC_ENV))
> > +				break;
> > +		}
> > +
> > +		if (time_after(jiffies, timeout))
> > +			return -ETIMEDOUT;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> The timeout code here is fragile.  If acquiring the spinlock takes more
> than a millisecond or if this thread gets interrupted or preempted then
> we could easily execute that loop just a single time, and fail.
> 
So what about moving the timeout initialization to right above the
while(1) loop?

> It would be better to retry a fixed number of times, say 1000?  That
> would take around 1 millisecond, but might be overkill.
> 
How long a 1000 times loop takes really depends on the cpu frequency,
right?

BTW, I have received the notification telling that the patch has been
applied on -mm tree.  So should I just send you an incremental patch
to address the comment?

-- 
Regards,
Shawn