rtc: rx8111: handle VLOW flag

Allow userspace to get battery status information and be able to warn when
battery is low and has to be replaced.
Tested-by: Waqar Hameed <waqar.hameed@axis.com>
Reviewed-by: Waqar Hameed <waqar.hameed@axis.com>
Link: https://lore.kernel.org/r/20240417191937.33790-2-alexandre.belloni@bootlin.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-rx8111.c

@@ -95,6 +95,9 @@ enum rx8111_regfield {
 	RX8111_REGF_INIEN,
 	RX8111_REGF_CHGEN,
 
+	/* RX8111_REG_STATUS_MON. */
+	RX8111_REGF_VLOW,
+
 	/* Sentinel value. */
 	RX8111_REGF_MAX
 };
@@ -129,6 +132,8 @@ static const struct reg_field rx8111_regfields[] = {
 	[RX8111_REGF_SWSEL1] = REG_FIELD(RX8111_REG_PWR_SWITCH_CTRL, 3, 3),
 	[RX8111_REGF_INIEN]  = REG_FIELD(RX8111_REG_PWR_SWITCH_CTRL, 6, 6),
 	[RX8111_REGF_CHGEN]  = REG_FIELD(RX8111_REG_PWR_SWITCH_CTRL, 7, 7),
+
+	[RX8111_REGF_VLOW]  = REG_FIELD(RX8111_REG_STATUS_MON, 1, 1),
 };
 
 static const struct regmap_config rx8111_regmap_config = {
@@ -276,6 +281,13 @@ static int rx8111_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
 
 		vlval = regval ? RTC_VL_DATA_INVALID : 0;
 
+		ret = regmap_field_read(data->regfields[RX8111_REGF_VLOW],
+					&regval);
+		if (ret)
+			return ret;
+
+		vlval |= regval ? RTC_VL_BACKUP_LOW : 0;
+
 		return put_user(vlval, (typeof(vlval) __user *)arg);
 	default:
 		return -ENOIOCTLCMD;