rtc: rv8803: invalidate date/time if alarm time is invalid

RTC core never calls rv8803_set_alarm with an invalid alarm time,
so if an invalid alarm time > 0 is set, external factors must have
corrupted the RTC's alarm time and possibly other registers.

Play it safe by marking the date/time invalid, so all registers are
reinitialized on a ->set_time.

This may cause existing setups to lose time if they so far set only
date/time, but ignored that the alarm registers had an invalid date
value, e.g.:

  rtc rtc0: invalid alarm value: 2020-3-27 7:82:0

These systems will have their ->get_time return -EINVAL till
->set_time initializes the alarm value (and sets a new time).
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20221123095527.2771434-3-s.hauer@pengutronix.deSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-rv8803.c

@@ -70,6 +70,7 @@ struct rv8803_data {
 	struct mutex flags_lock;
 	u8 ctrl;
 	u8 backup;
+	u8 alarm_invalid:1;
 	enum rv8803_type type;
 };
 
@@ -165,13 +166,13 @@ static int rv8803_regs_init(struct rv8803_data *rv8803)
 
 static int rv8803_regs_configure(struct rv8803_data *rv8803);
 
-static int rv8803_regs_reset(struct rv8803_data *rv8803)
+static int rv8803_regs_reset(struct rv8803_data *rv8803, bool full)
 {
 	/*
 	 * The RV-8803 resets all registers to POR defaults after voltage-loss,
 	 * the Epson RTCs don't, so we manually reset the remainder here.
 	 */
-	if (rv8803->type == rx_8803 || rv8803->type == rx_8900) {
+	if (full || rv8803->type == rx_8803 || rv8803->type == rx_8900) {
 		int ret = rv8803_regs_init(rv8803);
 		if (ret)
 			return ret;
@@ -238,6 +239,11 @@ static int rv8803_get_time(struct device *dev, struct rtc_time *tm)
 	u8 *date = date1;
 	int ret, flags;
 
+	if (rv8803->alarm_invalid) {
+		dev_warn(dev, "Corruption detected, data may be invalid.\n");
+		return -EINVAL;
+	}
+
 	flags = rv8803_read_reg(rv8803->client, RV8803_FLAG);
 	if (flags < 0)
 		return flags;
@@ -313,12 +319,19 @@ static int rv8803_set_time(struct device *dev, struct rtc_time *tm)
 		return flags;
 	}
 
-	if (flags & RV8803_FLAG_V2F) {
-		ret = rv8803_regs_reset(rv8803);
+	if ((flags & RV8803_FLAG_V2F) || rv8803->alarm_invalid) {
+		/*
+		 * If we sense corruption in the alarm registers, but see no
+		 * voltage loss flag, we can't rely on other registers having
+		 * sensible values. Reset them fully.
+		 */
+		ret = rv8803_regs_reset(rv8803, rv8803->alarm_invalid);
 		if (ret) {
 			mutex_unlock(&rv8803->flags_lock);
 			return ret;
 		}
+
+		rv8803->alarm_invalid = false;
 	}
 
 	ret = rv8803_write_reg(rv8803->client, RV8803_FLAG,
@@ -344,15 +357,33 @@ static int rv8803_get_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	if (flags < 0)
 		return flags;
 
+	alarmvals[0] &= 0x7f;
+	alarmvals[1] &= 0x3f;
+	alarmvals[2] &= 0x3f;
+
+	if (!bcd_is_valid(alarmvals[0]) ||
+	    !bcd_is_valid(alarmvals[1]) ||
+	    !bcd_is_valid(alarmvals[2]))
+		goto err_invalid;
+
 	alrm->time.tm_sec  = 0;
-	alrm->time.tm_min  = bcd2bin(alarmvals[0] & 0x7f);
-	alrm->time.tm_hour = bcd2bin(alarmvals[1] & 0x3f);
-	alrm->time.tm_mday = bcd2bin(alarmvals[2] & 0x3f);
+	alrm->time.tm_min  = bcd2bin(alarmvals[0]);
+	alrm->time.tm_hour = bcd2bin(alarmvals[1]);
+	alrm->time.tm_mday = bcd2bin(alarmvals[2]);
 
 	alrm->enabled = !!(rv8803->ctrl & RV8803_CTRL_AIE);
 	alrm->pending = (flags & RV8803_FLAG_AF) && alrm->enabled;
 
+	if ((unsigned int)alrm->time.tm_mday > 31 ||
+	    (unsigned int)alrm->time.tm_hour >= 24 ||
+	    (unsigned int)alrm->time.tm_min >= 60)
+		goto err_invalid;
+
 	return 0;
+
+err_invalid:
+	rv8803->alarm_invalid = true;
+	return -EINVAL;
 }
 
 static int rv8803_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)