rtc: ds1307: add support for m41t11

add m41t11 support in ds1307 driver. changes:

- add compatible string for m41t11
- check if RTC clock is running, if not
  enable the clock
Signed-off-by: NHeiko Schocher <hs@denx.de>

drivers/rtc/ds1307.c

@@ -23,6 +23,7 @@ enum ds_type {
 	ds_1307,
 	ds_1337,
 	ds_1340,
+	m41t11,
 	mcp794xx,
 };
 
@@ -260,6 +261,18 @@ read_rtc:
 		}
 	}
 
+	if (type == m41t11) {
+		/* clock halted?  turn it on, so clock can tick. */
+		if (buf[RTC_SEC_REG_ADDR] & RTC_SEC_BIT_CH) {
+			buf[RTC_SEC_REG_ADDR] &= ~RTC_SEC_BIT_CH;
+			dm_i2c_reg_write(dev, RTC_SEC_REG_ADDR,
+					 MCP7941X_BIT_ST);
+			dm_i2c_reg_write(dev, RTC_SEC_REG_ADDR,
+					 buf[RTC_SEC_REG_ADDR]);
+			goto read_rtc;
+		}
+	}
+
 	if (type == mcp794xx) {
 		/* make sure that the backup battery is enabled */
 		if (!(buf[RTC_DAY_REG_ADDR] & MCP7941X_BIT_VBATEN)) {
@@ -332,6 +345,7 @@ static const struct udevice_id ds1307_rtc_ids[] = {
 	{ .compatible = "dallas,ds1337", .data = ds_1337 },
 	{ .compatible = "dallas,ds1340", .data = ds_1340 },
 	{ .compatible = "microchip,mcp7941x", .data = mcp794xx },
+	{ .compatible = "st,m41t11", .data = m41t11 },
 	{ }
 };