rtc: rzn1: implement one-second accuracy for alarms

The hardware alarm only supports one-minute accuracy which is coarse and
disables UIE usage. Use the 1-second interrupt to achieve per-second
accuracy. It is activated once we hit the per-minute alarm. The new
feature is optional. When there is no 1-second interrupt, old behaviour
with per-minute accuracy is used as before. With this feature, all tests
of 'rtctest' are successfully passed.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250305101038.9933-2-wsa+renesas@sang-engineering.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Author: Wolfram Sang

drivers/rtc/rtc-rzn1.c

@@ -19,6 +19,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/rtc.h>
+#include <linux/spinlock.h>
 
 #define RZN1_RTC_CTL0 0x00
 #define   RZN1_RTC_CTL0_SLSB_SUBU 0
@@ -27,6 +28,7 @@
 #define   RZN1_RTC_CTL0_CE BIT(7)
 
 #define RZN1_RTC_CTL1 0x04
+#define   RZN1_RTC_CTL1_1SE BIT(3)
 #define   RZN1_RTC_CTL1_ALME BIT(4)
 
 #define RZN1_RTC_CTL2 0x08
@@ -58,6 +60,13 @@
 struct rzn1_rtc {
 	struct rtc_device *rtcdev;
 	void __iomem *base;
+	/*
+	 * Protects access to RZN1_RTC_CTL1 reg. rtc_lock with threaded_irqs
+	 * would introduce race conditions when switching interrupts because
+	 * of potential sleeps
+	 */
+	spinlock_t ctl1_access_lock;
+	struct rtc_time tm_alarm;
 };
 
 static void rzn1_rtc_get_time_snapshot(struct rzn1_rtc *rtc, struct rtc_time *tm)
@@ -135,23 +144,77 @@ static int rzn1_rtc_set_time(struct device *dev, struct rtc_time *tm)
 static irqreturn_t rzn1_rtc_alarm_irq(int irq, void *dev_id)
 {
 	struct rzn1_rtc *rtc = dev_id;
+	u32 ctl1, set_irq_bits = 0;
+
+	if (rtc->tm_alarm.tm_sec == 0)
+		rtc_update_irq(rtc->rtcdev, 1, RTC_AF | RTC_IRQF);
+	else
+		/* Switch to 1s interrupts */
+		set_irq_bits = RZN1_RTC_CTL1_1SE;
 
-	rtc_update_irq(rtc->rtcdev, 1, RTC_AF | RTC_IRQF);
+	guard(spinlock)(&rtc->ctl1_access_lock);
+
+	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+	ctl1 &= ~RZN1_RTC_CTL1_ALME;
+	ctl1 |= set_irq_bits;
+	writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t rzn1_rtc_1s_irq(int irq, void *dev_id)
+{
+	struct rzn1_rtc *rtc = dev_id;
+	u32 ctl1;
+
+	if (readl(rtc->base + RZN1_RTC_SECC) == bin2bcd(rtc->tm_alarm.tm_sec)) {
+		guard(spinlock)(&rtc->ctl1_access_lock);
+
+		ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+		ctl1 &= ~RZN1_RTC_CTL1_1SE;
+		writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+
+		rtc_update_irq(rtc->rtcdev, 1, RTC_AF | RTC_IRQF);
+	}
 
 	return IRQ_HANDLED;
 }
 
 static int rzn1_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
 {
 	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
-	u32 ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+	struct rtc_time *tm = &rtc->tm_alarm, tm_now;
+	u32 ctl1;
+	int ret;
 
-	if (enable)
-		ctl1 |= RZN1_RTC_CTL1_ALME;
-	else
-		ctl1 &= ~RZN1_RTC_CTL1_ALME;
+	guard(spinlock_irqsave)(&rtc->ctl1_access_lock);
 
-	writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+
+	if (enable) {
+		/*
+		 * Use alarm interrupt if alarm time is at least a minute away
+		 * or less than a minute but in the next minute. Otherwise use
+		 * 1 second interrupt to wait for the proper second
+		 */
+		do {
+			ctl1 &= ~(RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE);
+
+			ret = rzn1_rtc_read_time(dev, &tm_now);
+			if (ret)
+				return ret;
+
+			if (rtc_tm_sub(tm, &tm_now) > 59 || tm->tm_min != tm_now.tm_min)
+				ctl1 |= RZN1_RTC_CTL1_ALME;
+			else
+				ctl1 |= RZN1_RTC_CTL1_1SE;
+
+			writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+		} while (readl(rtc->base + RZN1_RTC_SECC) != bin2bcd(tm_now.tm_sec));
+	} else {
+		ctl1 &= ~(RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE);
+		writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+	}
 
 	return 0;
 }
@@ -185,7 +248,7 @@ static int rzn1_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	}
 
 	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
-	alrm->enabled = !!(ctl1 & RZN1_RTC_CTL1_ALME);
+	alrm->enabled = !!(ctl1 & (RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE));
 
 	return 0;
 }
@@ -216,6 +279,8 @@ static int rzn1_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	writel(bin2bcd(tm->tm_hour), rtc->base + RZN1_RTC_ALH);
 	writel(BIT(wday), rtc->base + RZN1_RTC_ALW);
 
+	rtc->tm_alarm = alrm->time;
+
 	rzn1_rtc_alarm_irq_enable(dev, alrm->enabled);
 
 	return 0;
@@ -304,7 +369,7 @@ static const struct rtc_class_ops rzn1_rtc_ops = {
 static int rzn1_rtc_probe(struct platform_device *pdev)
 {
 	struct rzn1_rtc *rtc;
-	int alarm_irq;
+	int irq;
 	int ret;
 
 	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
@@ -317,9 +382,9 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	if (IS_ERR(rtc->base))
 		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->base), "Missing reg\n");
 
-	alarm_irq = platform_get_irq(pdev, 0);
-	if (alarm_irq < 0)
-		return alarm_irq;
+	irq = platform_get_irq_byname(pdev, "alarm");
+	if (irq < 0)
+		return irq;
 
 	rtc->rtcdev = devm_rtc_allocate_device(&pdev->dev);
 	if (IS_ERR(rtc->rtcdev))
@@ -329,8 +394,6 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	rtc->rtcdev->range_max = RTC_TIMESTAMP_END_2099;
 	rtc->rtcdev->alarm_offset_max = 7 * 86400;
 	rtc->rtcdev->ops = &rzn1_rtc_ops;
-	set_bit(RTC_FEATURE_ALARM_RES_MINUTE, rtc->rtcdev->features);
-	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->rtcdev->features);
 
 	ret = devm_pm_runtime_enable(&pdev->dev);
 	if (ret < 0)
@@ -349,13 +412,24 @@ static int rzn1_rtc_probe(struct platform_device *pdev)
 	/* Disable all interrupts */
 	writel(0, rtc->base + RZN1_RTC_CTL1);
 
-	ret = devm_request_irq(&pdev->dev, alarm_irq, rzn1_rtc_alarm_irq, 0,
-			       dev_name(&pdev->dev), rtc);
+	spin_lock_init(&rtc->ctl1_access_lock);
+
+	ret = devm_request_irq(&pdev->dev, irq, rzn1_rtc_alarm_irq, 0, "RZN1 RTC Alarm", rtc);
 	if (ret) {
-		dev_err(&pdev->dev, "RTC timer interrupt not available\n");
+		dev_err(&pdev->dev, "RTC alarm interrupt not available\n");
 		goto dis_runtime_pm;
 	}
 
+	irq = platform_get_irq_byname_optional(pdev, "pps");
+	if (irq >= 0)
+		ret = devm_request_irq(&pdev->dev, irq, rzn1_rtc_1s_irq, 0, "RZN1 RTC 1s", rtc);
+
+	if (irq < 0 || ret) {
+		set_bit(RTC_FEATURE_ALARM_RES_MINUTE, rtc->rtcdev->features);
+		clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->rtcdev->features);
+		dev_warn(&pdev->dev, "RTC pps interrupt not available. Alarm has only minute accuracy\n");
+	}
+
 	ret = devm_rtc_register_device(rtc->rtcdev);
 	if (ret)
 		goto dis_runtime_pm;