rtc: ds1307: support m41t0 variant
The m41t0 variant is very similar to the already supported m41t00
variant, with the notable exception of the oscillator fail bit.
The data sheet notes:
If the oscillator fail (OF) bit is internally set to a '1,' this
indicates that the oscillator has either stopped, or was stopped
for some period of time and can be used to judge the validity of
the clock and date data.
The bit will get cleared with a regular write of the system time,
so no changes are needed to clear it.
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index f085b48..e294813 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -39,6 +39,7 @@
ds_1340,
ds_1388,
ds_3231,
+ m41t0,
m41t00,
mcp794xx,
rx_8025,
@@ -53,6 +54,7 @@
# 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 @@
{ "ds1388", ds_1388 },
{ "ds1340", ds_1340 },
{ "ds3231", ds_3231 },
+ { "m41t0", m41t0 },
{ "m41t00", m41t00 },
{ "mcp7940x", mcp794xx },
{ "mcp7941x", mcp794xx },
@@ -261,6 +264,7 @@
{ .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 @@
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 @@
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 @@
tmp = ds1307->regs[DS1307_REG_HOUR];
switch (ds1307->type) {
case ds_1340:
+ case m41t0:
case m41t00:
/*
* NOTE: ignores century bits; fix before deploying