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

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Message-ID: <2318694.E4xdUbedMD@ws-stein>
Date:   Tue, 13 Jun 2017 10:19:47 +0200
From:   Alexander Stein <alexander.stein@...tec-electronic.com>
To:     linux-kernel@...r.kernel.org
Cc:     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, dongas86@...il.com, kernel@...gutronix.de,
        arnd@...db.de, Anson Huang <Anson.Huang@....com>
Subject: Re: [PATCH V2 2/2] timer: imx-tpm: add imx tpm timer support

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?

Best regards,
Alexander