rtc: pcf2127: handle timestamp interrupts

commit 03623b4b ("rtc: pcf2127: add tamper detection support")
added support for timestamp interrupts. However they are not being
handled in the irq handler. If a timestamp interrupt occurs it
results in kernel disabling the interrupt and displaying the call
trace:

[  121.145580] irq 78: nobody cared (try booting with the "irqpoll" option)
...
[  121.238087] [<00000000c4d69393>] irq_default_primary_handler threaded [<000000000a90d25b>] pcf2127_rtc_irq [rtc_pcf2127]
[  121.248971] Disabling IRQ #78

Handle timestamp interrupts in pcf2127_rtc_irq(). Save time stamp
before clearing TSF1 and TSF2 flags so that it can't be overwritten.
Set a flag to mark if the timestamp is valid and only report to sysfs
if the flag is set. To mimic the hardware behavior, don’t save
another timestamp until the first one has been read by the userspace.

However, if the alarm irq is not configured, keep the old way of
handling timestamp interrupt in the timestamp0 sysfs calls.
Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
Reviewed-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Tested-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210629150643.31551-1-ykaukab@suse.de

drivers/rtc/rtc-pcf2127.c

@@ -94,10 +94,20 @@
 #define PCF2127_WD_VAL_MAX		255
 #define PCF2127_WD_VAL_DEFAULT		60
 
+/* Mask for currently enabled interrupts */
+#define PCF2127_CTRL1_IRQ_MASK (PCF2127_BIT_CTRL1_TSF1)
+#define PCF2127_CTRL2_IRQ_MASK ( \
+		PCF2127_BIT_CTRL2_AF | \
+		PCF2127_BIT_CTRL2_WDTF | \
+		PCF2127_BIT_CTRL2_TSF2)
+
 struct pcf2127 {
 	struct rtc_device *rtc;
 	struct watchdog_device wdd;
 	struct regmap *regmap;
+	time64_t ts;
+	bool ts_valid;
+	bool irq_enabled;
 };
 
 /*
@@ -434,22 +444,95 @@ static int pcf2127_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	return pcf2127_rtc_alarm_irq_enable(dev, alrm->enabled);
 }
 
+/*
+ * This function reads ctrl2 register, caller is responsible for calling
+ * pcf2127_wdt_active_ping()
+ */
+static int pcf2127_rtc_ts_read(struct device *dev, time64_t *ts)
+{
+	struct pcf2127 *pcf2127 = dev_get_drvdata(dev);
+	struct rtc_time tm;
+	int ret;
+	unsigned char data[25];
+
+	ret = regmap_bulk_read(pcf2127->regmap, PCF2127_REG_CTRL1, data,
+			       sizeof(data));
+	if (ret) {
+		dev_err(dev, "%s: read error ret=%d\n", __func__, ret);
+		return ret;
+	}
+
+	dev_dbg(dev,
+		"%s: raw data is cr1=%02x, cr2=%02x, cr3=%02x, ts_sc=%02x, ts_mn=%02x, ts_hr=%02x, ts_dm=%02x, ts_mo=%02x, ts_yr=%02x\n",
+		__func__, data[PCF2127_REG_CTRL1], data[PCF2127_REG_CTRL2],
+		data[PCF2127_REG_CTRL3], data[PCF2127_REG_TS_SC],
+		data[PCF2127_REG_TS_MN], data[PCF2127_REG_TS_HR],
+		data[PCF2127_REG_TS_DM], data[PCF2127_REG_TS_MO],
+		data[PCF2127_REG_TS_YR]);
+
+	tm.tm_sec = bcd2bin(data[PCF2127_REG_TS_SC] & 0x7F);
+	tm.tm_min = bcd2bin(data[PCF2127_REG_TS_MN] & 0x7F);
+	tm.tm_hour = bcd2bin(data[PCF2127_REG_TS_HR] & 0x3F);
+	tm.tm_mday = bcd2bin(data[PCF2127_REG_TS_DM] & 0x3F);
+	/* TS_MO register (month) value range: 1-12 */
+	tm.tm_mon = bcd2bin(data[PCF2127_REG_TS_MO] & 0x1F) - 1;
+	tm.tm_year = bcd2bin(data[PCF2127_REG_TS_YR]);
+	if (tm.tm_year < 70)
+		tm.tm_year += 100; /* assume we are in 1970...2069 */
+
+	ret = rtc_valid_tm(&tm);
+	if (ret) {
+		dev_err(dev, "Invalid timestamp. ret=%d\n", ret);
+		return ret;
+	}
+
+	*ts = rtc_tm_to_time64(&tm);
+	return 0;
+};
+
+static void pcf2127_rtc_ts_snapshot(struct device *dev)
+{
+	struct pcf2127 *pcf2127 = dev_get_drvdata(dev);
+	int ret;
+
+	/* Let userspace read the first timestamp */
+	if (pcf2127->ts_valid)
+		return;
+
+	ret = pcf2127_rtc_ts_read(dev, &pcf2127->ts);
+	if (!ret)
+		pcf2127->ts_valid = true;
+}
+
 static irqreturn_t pcf2127_rtc_irq(int irq, void *dev)
 {
 	struct pcf2127 *pcf2127 = dev_get_drvdata(dev);
-	unsigned int ctrl2 = 0;
+	unsigned int ctrl1, ctrl2;
 	int ret = 0;
 
+	ret = regmap_read(pcf2127->regmap, PCF2127_REG_CTRL1, &ctrl1);
+	if (ret)
+		return IRQ_NONE;
+
 	ret = regmap_read(pcf2127->regmap, PCF2127_REG_CTRL2, &ctrl2);
 	if (ret)
 		return IRQ_NONE;
 
-	if (!(ctrl2 & PCF2127_BIT_CTRL2_AF))
+	if (!(ctrl1 & PCF2127_CTRL1_IRQ_MASK || ctrl2 & PCF2127_CTRL2_IRQ_MASK))
 		return IRQ_NONE;
 
+	if (ctrl1 & PCF2127_BIT_CTRL1_TSF1 || ctrl2 & PCF2127_BIT_CTRL2_TSF2)
+		pcf2127_rtc_ts_snapshot(dev);
+
+	if (ctrl1 & PCF2127_CTRL1_IRQ_MASK)
+		regmap_write(pcf2127->regmap, PCF2127_REG_CTRL1,
+			ctrl1 & ~PCF2127_CTRL1_IRQ_MASK);
+
+	if (ctrl2 & PCF2127_CTRL2_IRQ_MASK)
 		regmap_write(pcf2127->regmap, PCF2127_REG_CTRL2,
-		     ctrl2 & ~(PCF2127_BIT_CTRL2_AF | PCF2127_BIT_CTRL2_WDTF));
+			ctrl2 & ~PCF2127_CTRL2_IRQ_MASK);
 
+	if (ctrl2 & PCF2127_BIT_CTRL2_AF)
 		rtc_update_irq(pcf2127->rtc, 1, RTC_IRQF | RTC_AF);
 
 	pcf2127_wdt_active_ping(&pcf2127->wdd);
@@ -475,6 +558,9 @@ static ssize_t timestamp0_store(struct device *dev,
 	struct pcf2127 *pcf2127 = dev_get_drvdata(dev->parent);
 	int ret;
 
+	if (pcf2127->irq_enabled) {
+		pcf2127->ts_valid = false;
+	} else {
 		ret = regmap_update_bits(pcf2127->regmap, PCF2127_REG_CTRL1,
 			PCF2127_BIT_CTRL1_TSF1, 0);
 		if (ret) {
@@ -492,6 +578,7 @@ static ssize_t timestamp0_store(struct device *dev,
 		ret = pcf2127_wdt_active_ping(&pcf2127->wdd);
 		if (ret)
 			return ret;
+	}
 
 	return count;
 };
@@ -500,50 +587,36 @@ static ssize_t timestamp0_show(struct device *dev,
 			       struct device_attribute *attr, char *buf)
 {
 	struct pcf2127 *pcf2127 = dev_get_drvdata(dev->parent);
-	struct rtc_time tm;
+	unsigned int ctrl1, ctrl2;
 	int ret;
-	unsigned char data[25];
+	time64_t ts;
 
-	ret = regmap_bulk_read(pcf2127->regmap, PCF2127_REG_CTRL1, data,
-			       sizeof(data));
-	if (ret) {
-		dev_err(dev, "%s: read error ret=%d\n", __func__, ret);
-		return ret;
-	}
-
-	dev_dbg(dev,
-		"%s: raw data is cr1=%02x, cr2=%02x, cr3=%02x, ts_sc=%02x, "
-		"ts_mn=%02x, ts_hr=%02x, ts_dm=%02x, ts_mo=%02x, ts_yr=%02x\n",
-		__func__, data[PCF2127_REG_CTRL1], data[PCF2127_REG_CTRL2],
-		data[PCF2127_REG_CTRL3], data[PCF2127_REG_TS_SC],
-		data[PCF2127_REG_TS_MN], data[PCF2127_REG_TS_HR],
-		data[PCF2127_REG_TS_DM], data[PCF2127_REG_TS_MO],
-		data[PCF2127_REG_TS_YR]);
+	if (pcf2127->irq_enabled) {
+		if (!pcf2127->ts_valid)
+			return 0;
+		ts = pcf2127->ts;
+	} else {
+		ret = regmap_read(pcf2127->regmap, PCF2127_REG_CTRL1, &ctrl1);
+		if (ret)
+			return 0;
 
-	ret = pcf2127_wdt_active_ping(&pcf2127->wdd);
+		ret = regmap_read(pcf2127->regmap, PCF2127_REG_CTRL2, &ctrl2);
 		if (ret)
-		return ret;
+			return 0;
 
-	if (!(data[PCF2127_REG_CTRL1] & PCF2127_BIT_CTRL1_TSF1) &&
-	    !(data[PCF2127_REG_CTRL2] & PCF2127_BIT_CTRL2_TSF2))
+		if (!(ctrl1 & PCF2127_BIT_CTRL1_TSF1) &&
+		    !(ctrl2 & PCF2127_BIT_CTRL2_TSF2))
 			return 0;
 
-	tm.tm_sec = bcd2bin(data[PCF2127_REG_TS_SC] & 0x7F);
-	tm.tm_min = bcd2bin(data[PCF2127_REG_TS_MN] & 0x7F);
-	tm.tm_hour = bcd2bin(data[PCF2127_REG_TS_HR] & 0x3F);
-	tm.tm_mday = bcd2bin(data[PCF2127_REG_TS_DM] & 0x3F);
-	/* TS_MO register (month) value range: 1-12 */
-	tm.tm_mon = bcd2bin(data[PCF2127_REG_TS_MO] & 0x1F) - 1;
-	tm.tm_year = bcd2bin(data[PCF2127_REG_TS_YR]);
-	if (tm.tm_year < 70)
-		tm.tm_year += 100; /* assume we are in 1970...2069 */
+		ret = pcf2127_rtc_ts_read(dev->parent, &ts);
+		if (ret)
+			return 0;
 
-	ret = rtc_valid_tm(&tm);
+		ret = pcf2127_wdt_active_ping(&pcf2127->wdd);
 		if (ret)
 			return ret;
-
-	return sprintf(buf, "%llu\n",
-		       (unsigned long long)rtc_tm_to_time64(&tm));
+	}
+	return sprintf(buf, "%llu\n", (unsigned long long)ts);
 };
 
 static DEVICE_ATTR_RW(timestamp0);
@@ -594,6 +667,7 @@ static int pcf2127_probe(struct device *dev, struct regmap *regmap,
 			dev_err(dev, "failed to request alarm irq\n");
 			return ret;
 		}
+		pcf2127->irq_enabled = true;
 	}
 
 	if (alarm_irq > 0 || device_property_read_bool(dev, "wakeup-source")) {