On 11/03/2016 04:36 PM, Mark Rutland wrote:

On Thu, Nov 03, 2016 at 03:29:24PM +0100, Neil Armstrong wrote:

quoted

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?

It's part of the Always-ON APB registers, there is no clear IP block here,
but it seems to be like a scratch register shared with the BL3 FW.

quoted

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.

The register seems to never change, and it seems to be an indication for the
FW when it enters the suspend mode.

quoted

+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.

Actually the vendor tree uses a 64bit running counter to provide this
but with a fixed start date.

quoted

+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?

It seems to be managed by the BL3 FW. We have no details on the underlying implementation.

quoted

+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.