drivers/rtc/rtc_mc146818.c: Add input clock config to driver

This commit adds input clock selection to the RTC driver. This
is required to allow for the real hardware to operate. The
QEMU emulated hardware ignores the input clock settings.

Signed-off-by: Bjarki Arge Andreasen <bjarkix123@gmail.com>

drivers/rtc/rtc_mc146818.c

@@ -113,6 +113,11 @@
 #define MIN_YEAR_DIFF	0 /* YEAR - 1900 */
 #define MAX_YEAR_DIFF	99 /* YEAR - 1999 */
 
+/* Input clock frequency mapped to divider bits */
+#define RTC_IN_CLK_DIV_BITS_4194304 (0)
+#define RTC_IN_CLK_DIV_BITS_1048576 (1 << 4)
+#define RTC_IN_CLK_DIV_BITS_32768   (2 << 4)
+
 struct rtc_mc146818_data {
 	struct k_spinlock lock;
 	bool alarm_pending;
@@ -509,7 +514,10 @@ struct rtc_driver_api rtc_mc146818_driver_api = {
 #define RTC_MC146818_INIT_FN_DEFINE(n)						\
 	static int rtc_mc146818_init##n(const struct device *dev)		\
 	{									\
-		rtc_write(RTC_REG_A, 0);					\
+		rtc_write(RTC_REG_A,						\
+			  _CONCAT(RTC_IN_CLK_DIV_BITS_,				\
+				  DT_INST_PROP(n, clock_frequency)));		\
+										\
 		rtc_write(RTC_REG_B, RTC_DMODE_BIT | RTC_HFORMAT_BIT);		\
 										\
 		IRQ_CONNECT(DT_INST_IRQN(0),					\

dts/bindings/rtc/motorola,mc146818.yaml

@@ -7,3 +7,13 @@ description: Motorola MC146818 compatible Real Timer Clock
 compatible: "motorola,mc146818"
 
 include: rtc-device.yaml
+
+properties:
+  clock-frequency:
+    type: int
+    default: 32768
+    enum:
+      - 4194304
+      - 1048576
+      - 32768
+    description: Frequency of the input-clock in Hertz (Hz)