rtc: tps6594: Add power management support

Add power management support to the driver. This allows a SoC to wake
from suspend using the nINT provided by the RTC.
It takes care of the case when the interrupt has not been caught because
the kernel has not yet woke up.
(This is the case when only edges interrupt are caught)

Signed-off-by: Richard Genoud <richard.genoud@bootlin.com>
Link: https://lore.kernel.org/r/20240618141851.1810000-4-richard.genoud@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Author: richard-bootlin

drivers/rtc/rtc-tps6594.c

@@ -44,6 +44,7 @@
 
 struct tps6594_rtc {
 	struct rtc_device *rtc_dev;
+	int irq;
 };
 
 static int tps6594_rtc_alarm_irq_enable(struct device *dev,
@@ -419,6 +420,8 @@ static int tps6594_rtc_probe(struct platform_device *pdev)
 	if (irq < 0)
 		return dev_err_probe(dev, irq, "Failed to get irq\n");
 
+	rtc->irq = irq;
+
 	ret = devm_request_threaded_irq(dev, irq, NULL, tps6594_rtc_interrupt,
 					IRQF_ONESHOT, TPS6594_IRQ_NAME_ALARM,
 					dev);
@@ -438,6 +441,49 @@ static int tps6594_rtc_probe(struct platform_device *pdev)
 	return devm_rtc_register_device(rtc->rtc_dev);
 }
 
+static int tps6594_rtc_resume(struct device *dev)
+{
+	struct tps6594 *tps = dev_get_drvdata(dev->parent);
+	struct tps6594_rtc *rtc = dev_get_drvdata(dev);
+	int ret;
+
+	ret = regmap_test_bits(tps->regmap, TPS6594_REG_INT_STARTUP,
+			       TPS6594_BIT_RTC_INT);
+	if (ret < 0) {
+		dev_err(dev, "failed to read REG_INT_STARTUP: %d\n", ret);
+		goto out;
+	}
+
+	if (ret > 0) {
+		/*
+		 * If the alarm bit is set, it means that the IRQ has been
+		 * fired. But, the kernel may not have woke up yet when it
+		 * happened. So, we have to clear it.
+		 */
+		ret = regmap_write(tps->regmap, TPS6594_REG_RTC_STATUS,
+				   TPS6594_BIT_ALARM);
+		if (ret < 0)
+			dev_err(dev, "error clearing alarm bit: %d", ret);
+
+		rtc_update_irq(rtc->rtc_dev, 1, RTC_IRQF | RTC_AF);
+	}
+out:
+	disable_irq_wake(rtc->irq);
+
+	return 0;
+}
+
+static int tps6594_rtc_suspend(struct device *dev)
+{
+	struct tps6594_rtc *rtc = dev_get_drvdata(dev);
+
+	enable_irq_wake(rtc->irq);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(tps6594_rtc_pm_ops, tps6594_rtc_suspend, tps6594_rtc_resume);
+
 static const struct platform_device_id tps6594_rtc_id_table[] = {
 	{ "tps6594-rtc", },
 	{}
@@ -448,6 +494,7 @@ static struct platform_driver tps6594_rtc_driver = {
 	.probe		= tps6594_rtc_probe,
 	.driver		= {
 		.name	= "tps6594-rtc",
+		.pm = pm_sleep_ptr(&tps6594_rtc_pm_ops),
 	},
 	.id_table = tps6594_rtc_id_table,
 };