rtc: cmos: Report supported alarm limit to rtc infrastructure

The alarm window supported by the cmos RTC depends on the chip
and its configuration. Report the limit to the RTC core.

Cc: Brian Norris <briannorris@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230817225537.4053865-5-linux@roeck-us.net
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

Author: groeck

drivers/rtc/rtc-cmos.c

@@ -913,6 +913,10 @@ static inline void cmos_check_acpi_rtc_status(struct device *dev,
 #define	INITSECTION	__init
 #endif
 
+#define SECS_PER_DAY	(24 * 60 * 60)
+#define SECS_PER_MONTH	(28 * SECS_PER_DAY)
+#define SECS_PER_YEAR	(365 * SECS_PER_DAY)
+
 static int INITSECTION
 cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
 {
@@ -1019,6 +1023,13 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
 		goto cleanup0;
 	}
 
+	if (cmos_rtc.mon_alrm)
+		cmos_rtc.rtc->alarm_offset_max = SECS_PER_YEAR - 1;
+	else if (cmos_rtc.day_alrm)
+		cmos_rtc.rtc->alarm_offset_max = SECS_PER_MONTH - 1;
+	else
+		cmos_rtc.rtc->alarm_offset_max = SECS_PER_DAY - 1;
+
 	rename_region(ports, dev_name(&cmos_rtc.rtc->dev));
 
 	if (!mc146818_does_rtc_work()) {