linux-kernel - Re: [RFC PATCH 2/3] rtc: Add Amlogic Virtual Wake RTC

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Date:   Thu, 3 Nov 2016 15:36:48 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     khilman@...libre.com, carlo@...one.org, a.zummo@...ertech.it,
        alexandre.belloni@...e-electrons.com,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, rtc-linux@...glegroups.com
Subject: Re: [RFC PATCH 2/3] rtc: Add Amlogic Virtual Wake RTC

On Thu, Nov 03, 2016 at 03:29:24PM +0100, Neil Armstrong wrote:
> The Amlogic Meson GX SoCs uses a special register to store the
> time in seconds to wakeup after a system suspend.

Where does this register live, exactly? What IP block is it part of?

> In order to be able to reuse the RTC wakealarm feature, this
> driver implements a fake RTC device which uses the system time
> to deduce a suspend delay.

This sounds like an always-on oneshot timer device, not an RTC.

> +static int meson_vrtc_read_time(struct device *dev, struct rtc_time *tm)
> +{
> +	unsigned long local_time;
> +	struct timeval time;
> +
> +	do_gettimeofday(&time);
> +	local_time = time.tv_sec - (sys_tz.tz_minuteswest * 60);
> +	rtc_time_to_tm(local_time, tm);
> +
> +	return 0;
> +}

... if this were a timer, you wouldn't need this hack.

> +static int meson_vrtc_probe(struct platform_device *pdev)
> +{
> +	struct meson_vrtc_data *vrtc;
> +	struct resource *res;
> +
> +	vrtc = devm_kzalloc(&pdev->dev, sizeof(*vrtc), GFP_KERNEL);
> +	if (!vrtc)
> +		return -ENOMEM;
> +
> +	vrtc->pdev = pdev;
> +
> +	/* Alarm registers */
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	vrtc->io_alarm = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(vrtc->io_alarm))
> +		return PTR_ERR(vrtc->io_alarm);
> +
> +	device_init_wakeup(&pdev->dev, 1);
> +
> +	platform_set_drvdata(pdev, vrtc);
> +
> +	vrtc->rtc = devm_rtc_device_register(&pdev->dev, "meson-vrtc",
> +			&meson_vrtc_ops, THIS_MODULE);
> +	if (IS_ERR(vrtc->rtc))
> +		return PTR_ERR(vrtc->rtc);
> +
> +	return 0;
> +}

I see that no interrupt is described. How exactly does this wake the system
from suspend? Is there some interrupt managed by FW for this, for example?

> +static const struct of_device_id meson_vrtc_dt_match[] = {
> +	{ .compatible = "amlogic,meson-vrtc"},

There was no binding documentation in this patch series.

Thanks,
Mark.