Date: Mon, 19 Jun 2017 23:36:39 +0800
From: Dong Aisheng <dongas86@gmail.com>
To: Alexander Stein <alexander.stein@systec-electronic.com>
Cc: linux-kernel@vger.kernel.org, Dong Aisheng <aisheng.dong@nxp.com>,
        linux-arm-kernel@lists.infradead.org, daniel.lezcano@linaro.org,
        tglx@linutronix.de, shawnguo@kernel.org, ping.bai@nxp.com,
        anson.huang@nxp.com, kernel@pengutronix.de, arnd@arndb.de
Subject: Re: [PATCH V2 2/2] timer: imx-tpm: add imx tpm timer support
Message-ID: <20170619153638.GB8913@b29396-OptiPlex-7040>
References: <1497340725-26594-1-git-send-email-aisheng.dong@nxp.com>
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 <2318694.E4xdUbedMD@ws-stein>
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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