rtc: Add MCP79411 support to DS1307 rtc driver

The code is from Adrian Cox, and is patterned after similar
support in Linux (drivers/rtc/rtc-ds1307.c:1121-1135). This
chip is used on the Cyrus board from Varisys.

Signed-off-by: Andy Fleming <afleming@gmail.com>
Reviewed-by: York Sun <yorksun@freescale.com>

drivers/rtc/Makefile

@@ -4,7 +4,6 @@
 #
 # SPDX-License-Identifier:	GPL-2.0+
 #
-
 #ccflags-y += -DDEBUG
 
 obj-$(CONFIG_DM_RTC) += rtc-uclass.o
@@ -37,6 +36,7 @@ obj-$(CONFIG_RTC_M48T35A) += m48t35ax.o
 obj-$(CONFIG_RTC_MAX6900) += max6900.o
 obj-$(CONFIG_RTC_MC13XXX) += mc13xxx-rtc.o
 obj-$(CONFIG_RTC_MC146818) += mc146818.o
+obj-$(CONFIG_RTC_MCP79411) += ds1307.o
 obj-$(CONFIG_MCFRTC) += mcfrtc.o
 obj-$(CONFIG_RTC_MK48T59) += mk48t59.o
 obj-$(CONFIG_RTC_MPC5200) += mpc5xxx.o

drivers/rtc/ds1307.c

@@ -58,6 +58,10 @@
 #define RTC_CTL_BIT_SQWE	0x10	/* Square Wave Enable           */
 #define RTC_CTL_BIT_OUT		0x80	/* Output Control               */
 
+/* MCP7941X-specific bits */
+#define MCP7941X_BIT_ST		0x80
+#define MCP7941X_BIT_VBATEN	0x08
+
 static uchar rtc_read (uchar reg);
 static void rtc_write (uchar reg, uchar val);
 
@@ -69,6 +73,9 @@ int rtc_get (struct rtc_time *tmp)
 	int rel = 0;
 	uchar sec, min, hour, mday, wday, mon, year;
 
+#ifdef CONFIG_RTC_MCP79411
+read_rtc:
+#endif
 	sec = rtc_read (RTC_SEC_REG_ADDR);
 	min = rtc_read (RTC_MIN_REG_ADDR);
 	hour = rtc_read (RTC_HR_REG_ADDR);
@@ -81,6 +88,7 @@ int rtc_get (struct rtc_time *tmp)
 		"hr: %02x min: %02x sec: %02x\n",
 		year, mon, mday, wday, hour, min, sec);
 
+#ifdef CONFIG_RTC_DS1307
 	if (sec & RTC_SEC_BIT_CH) {
 		printf ("### Warning: RTC oscillator has stopped\n");
 		/* clear the CH flag */
@@ -88,6 +96,23 @@ int rtc_get (struct rtc_time *tmp)
 			   rtc_read (RTC_SEC_REG_ADDR) & ~RTC_SEC_BIT_CH);
 		rel = -1;
 	}
+#endif
+
+#ifdef CONFIG_RTC_MCP79411
+	/* make sure that the backup battery is enabled */
+	if (!(wday & MCP7941X_BIT_VBATEN)) {
+		rtc_write(RTC_DAY_REG_ADDR,
+			  wday | MCP7941X_BIT_VBATEN);
+	}
+
+	/* clock halted?  turn it on, so clock can tick. */
+	if (!(sec & MCP7941X_BIT_ST)) {
+		rtc_write(RTC_SEC_REG_ADDR, MCP7941X_BIT_ST);
+		printf("Started RTC\n");
+		goto read_rtc;
+	}
+#endif
+
 
 	tmp->tm_sec  = bcd2bin (sec & 0x7F);
 	tmp->tm_min  = bcd2bin (min & 0x7F);
@@ -121,11 +146,20 @@ int rtc_set (struct rtc_time *tmp)
 
 	rtc_write (RTC_YR_REG_ADDR, bin2bcd (tmp->tm_year % 100));
 	rtc_write (RTC_MON_REG_ADDR, bin2bcd (tmp->tm_mon));
+#ifdef CONFIG_RTC_MCP79411
+	rtc_write (RTC_DAY_REG_ADDR,
+		   bin2bcd (tmp->tm_wday + 1) | MCP7941X_BIT_VBATEN);
+#else
 	rtc_write (RTC_DAY_REG_ADDR, bin2bcd (tmp->tm_wday + 1));
+#endif
 	rtc_write (RTC_DATE_REG_ADDR, bin2bcd (tmp->tm_mday));
 	rtc_write (RTC_HR_REG_ADDR, bin2bcd (tmp->tm_hour));
 	rtc_write (RTC_MIN_REG_ADDR, bin2bcd (tmp->tm_min));
+#ifdef CONFIG_RTC_MCP79411
+	rtc_write (RTC_SEC_REG_ADDR, bin2bcd (tmp->tm_sec) | MCP7941X_BIT_ST);
+#else
 	rtc_write (RTC_SEC_REG_ADDR, bin2bcd (tmp->tm_sec));
+#endif
 
 	return 0;
 }