2 files changed, 14 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/i2c/trivial-devices.txt b/Documentation/devicetree/bindings/i2c/trivial-devices.txt
index ad10fbe61562..3e0a34c88e07 100644
--- a/Documentation/devicetree/bindings/i2c/trivial-devices.txt
+++ b/Documentation/devicetree/bindings/i2c/trivial-devices.txt
@@ -160,6 +160,7 @@ sii,s35390a		2-wire CMOS real-time clock
 silabs,si7020           Relative Humidity and Temperature Sensors
 skyworks,sky81452       Skyworks SKY81452: Six-Channel White LED Driver with Touch Panel Bias Supply
 st,24c256               i2c serial eeprom  (24cxx)
+st,m41t0                Serial real-time clock (RTC)
 st,m41t00               Serial real-time clock (RTC)
 st,m41t62               Serial real-time clock (RTC) with alarm
 st,m41t80               M41T80 - SERIAL ACCESS RTC WITH ALARMS
diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index f085b487bbe7..e29481391496 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -39,6 +39,7 @@ enum ds_type {
         ds_1340,
         ds_1388,
         ds_3231,
+        m41t0,
         m41t00,
         mcp794xx,
         rx_8025,
@@ -53,6 +54,7 @@ enum ds_type {
 #       define DS1340_BIT_nEOSC         0x80
 #       define MCP794XX_BIT_ST          0x80
 #define DS1307_REG_MIN          0x01    /* 00-59 */
+#       define M41T0_BIT_OF             0x80
 #define DS1307_REG_HOUR         0x02    /* 00-23, or 1-12{am,pm} */
 #       define DS1307_BIT_12HR          0x40    /* in REG_HOUR */
 #       define DS1307_BIT_PM            0x20    /* in REG_HOUR */
@@ -183,6 +185,7 @@ static const struct i2c_device_id ds1307_id[] = {
         { "ds1388", ds_1388 },
         { "ds1340", ds_1340 },
         { "ds3231", ds_3231 },
+        { "m41t0", m41t0 },
         { "m41t00", m41t00 },
         { "mcp7940x", mcp794xx },
         { "mcp7941x", mcp794xx },
@@ -261,6 +264,7 @@ static const struct acpi_device_id ds1307_acpi_ids[] = {
         { .id = "DS1388", .driver_data = ds_1388 },
         { .id = "DS1340", .driver_data = ds_1340 },
         { .id = "DS3231", .driver_data = ds_3231 },
+        { .id = "M41T0", .driver_data = m41t0 },
         { .id = "M41T00", .driver_data = m41t00 },
         { .id = "MCP7940X", .driver_data = mcp794xx },
         { .id = "MCP7941X", .driver_data = mcp794xx },
@@ -456,6 +460,13 @@ static int ds1307_get_time(struct device *dev, struct rtc_time *t)
 
         dev_dbg(dev, "%s: %7ph\n", "read", ds1307->regs);
 
+        /* if oscillator fail bit is set, no data can be trusted */
+        if (ds1307->type == m41t0 &&
+            ds1307->regs[DS1307_REG_MIN] & M41T0_BIT_OF) {
+                dev_warn_once(dev, "oscillator failed, set time!\n");
+                return -EINVAL;
+        }
+
         t->tm_sec = bcd2bin(ds1307->regs[DS1307_REG_SECS] & 0x7f);
         t->tm_min = bcd2bin(ds1307->regs[DS1307_REG_MIN] & 0x7f);
         tmp = ds1307->regs[DS1307_REG_HOUR] & 0x3f;
@@ -1578,6 +1589,7 @@ read_rtc:
         tmp = ds1307->regs[DS1307_REG_SECS];
         switch (ds1307->type) {
         case ds_1307:
+        case m41t0:
         case m41t00:
                 /* clock halted?  turn it on, so clock can tick. */
                 if (tmp & DS1307_BIT_CH) {
@@ -1642,6 +1654,7 @@ read_rtc:
         tmp = ds1307->regs[DS1307_REG_HOUR];
         switch (ds1307->type) {
         case ds_1340:
+        case m41t0:
         case m41t00:
                 /*
                  * NOTE: ignores century bits; fix before deploying