linux-kernel - Re: [PATCH V2 2/2] timer: imx-tpm: add imx tpm timer support

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Date:   Mon, 19 Jun 2017 23:36:39 +0800
From:   Dong Aisheng <dongas86@...il.com>
To:     Alexander Stein <alexander.stein@...tec-electronic.com>
Cc:     linux-kernel@...r.kernel.org, Dong Aisheng <aisheng.dong@....com>,
        linux-arm-kernel@...ts.infradead.org, daniel.lezcano@...aro.org,
        tglx@...utronix.de, shawnguo@...nel.org, ping.bai@....com,
        anson.huang@....com, kernel@...gutronix.de, arnd@...db.de
Subject: Re: [PATCH V2 2/2] timer: imx-tpm: add imx tpm timer support

On Tue, Jun 13, 2017 at 10:19:47AM +0200, Alexander Stein wrote:
> On Tuesday 13 June 2017 15:58:45, Dong Aisheng wrote:
> > diff --git a/drivers/clocksource/timer-imx-tpm.c
> > b/drivers/clocksource/timer-imx-tpm.c new file mode 100644
> > index 0000000..940a4f75
> > --- /dev/null
> > +++ b/drivers/clocksource/timer-imx-tpm.c
> > @@ -0,0 +1,227 @@
> > [...]
> > +static int tpm_set_next_event(unsigned long delta,
> > +				struct clock_event_device *evt)
> > +{
> > +	unsigned long next, now;
> > +
> > +	next = readl(timer_base + TPM_CNT) + delta;
> > +	writel(next, timer_base + TPM_C0V);
> > +	now = readl(timer_base + TPM_CNT);
> 
> What about:
> > now = readl(timer_base + TPM_CNT);
> > next = now + delta;
> > writel(next, timer_base + TPM_C0V);
> > return 0;
> 
> > +	return (int)((next - now) <= 0) ? -ETIME : 0;
> 
> Can this error actually happen, even with your implementation?

Yes, i did observe some -ETIME when testing with nanosleep or
hrtimer during programing min_delta event, especially when system
is high loading. e.g. run GPU stress test.

Please also refer to another mail for details i just replied to Daniel.

Regards
Dong Aisheng