rtc: ds1307: fix century bit support
Add an option to properly support the century bit of ds1337 and compatibles
and ds1340.
Because the driver had a bug until now, it is not possible to switch users
to the fixed code directly as RTCs in the field will wrongly have the
century bit set.
Acked-by: Arnaud Ebalard <arno@natisbad.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 7fc11cd..6ce3dad 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -234,6 +234,20 @@
Say Y here if you want to expose temperature sensor data on
rtc-ds1307 (only DS3231)
+config RTC_DRV_DS1307_CENTURY
+ bool "Century bit support for rtc-ds1307"
+ depends on RTC_DRV_DS1307
+ default n
+ help
+ The DS1307 driver suffered from a bug where it was enabling the
+ century bit inconditionnally but never used it when reading the time.
+ It made the driver unable to support dates beyond 2099.
+ Setting this option will add proper support for the century bit but if
+ the time was previously set using a kernel predating this option,
+ reading the date will return a date in the next century.
+ To solve that, you could boot a kernel without this option set, set
+ the RTC date and then boot a kernel with this option set.
+
config RTC_DRV_DS1374
tristate "Dallas/Maxim DS1374"
help
diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index 8e1c5cb..712e221 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -382,10 +382,25 @@
t->tm_mday = bcd2bin(ds1307->regs[DS1307_REG_MDAY] & 0x3f);
tmp = ds1307->regs[DS1307_REG_MONTH] & 0x1f;
t->tm_mon = bcd2bin(tmp) - 1;
-
- /* assume 20YY not 19YY, and ignore DS1337_BIT_CENTURY */
t->tm_year = bcd2bin(ds1307->regs[DS1307_REG_YEAR]) + 100;
+#ifdef CONFIG_RTC_DRV_DS1307_CENTURY
+ switch (ds1307->type) {
+ case ds_1337:
+ case ds_1339:
+ case ds_3231:
+ if (ds1307->regs[DS1307_REG_MONTH] & DS1337_BIT_CENTURY)
+ t->tm_year += 100;
+ break;
+ case ds_1340:
+ if (ds1307->regs[DS1307_REG_HOUR] & DS1340_BIT_CENTURY)
+ t->tm_year += 100;
+ break;
+ default:
+ break;
+ }
+#endif
+
dev_dbg(dev, "%s secs=%d, mins=%d, "
"hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
"read", t->tm_sec, t->tm_min,
@@ -409,6 +424,27 @@
t->tm_hour, t->tm_mday,
t->tm_mon, t->tm_year, t->tm_wday);
+#ifdef CONFIG_RTC_DRV_DS1307_CENTURY
+ if (t->tm_year < 100)
+ return -EINVAL;
+
+ switch (ds1307->type) {
+ case ds_1337:
+ case ds_1339:
+ case ds_3231:
+ case ds_1340:
+ if (t->tm_year > 299)
+ return -EINVAL;
+ default:
+ if (t->tm_year > 199)
+ return -EINVAL;
+ break;
+ }
+#else
+ if (t->tm_year < 100 || t->tm_year > 199)
+ return -EINVAL;
+#endif
+
buf[DS1307_REG_SECS] = bin2bcd(t->tm_sec);
buf[DS1307_REG_MIN] = bin2bcd(t->tm_min);
buf[DS1307_REG_HOUR] = bin2bcd(t->tm_hour);
@@ -424,11 +460,13 @@
case ds_1337:
case ds_1339:
case ds_3231:
- buf[DS1307_REG_MONTH] |= DS1337_BIT_CENTURY;
+ if (t->tm_year > 199)
+ buf[DS1307_REG_MONTH] |= DS1337_BIT_CENTURY;
break;
case ds_1340:
- buf[DS1307_REG_HOUR] |= DS1340_BIT_CENTURY_EN
- | DS1340_BIT_CENTURY;
+ buf[DS1307_REG_HOUR] |= DS1340_BIT_CENTURY_EN;
+ if (t->tm_year > 199)
+ buf[DS1307_REG_HOUR] |= DS1340_BIT_CENTURY;
break;
case mcp794xx:
/*