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 7fc11cdfd27ef570db893b6f92679071903b6429..6ce3dad732533055c57007e0911c48005e9df67c 100644 (file)
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -234,6 +234,20 @@ config RTC_DRV_DS1307_HWMON
          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 8e1c5cb6ece6f60619e5cafcea4271e056d96778..712e221d2415f32108938083641f09b41a4e433f 100644 (file)
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -382,10 +382,25 @@ static int ds1307_get_time(struct device *dev, struct rtc_time *t)
        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 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
                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 @@ static int ds1307_set_time(struct device *dev, struct rtc_time *t)
        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:
                /*