rtc: ds1307: Fix relying on reset value for weekday

commit e29385fab0bf94017fac130ee32f5bb2daf74417 upstream.

The reset value of weekday is 0x1. This is wrong since
the reset values of the day/month/year make up to Jan 1 2001.
When computed weekday comes out to be Monday. On a scale
of 1-7(Sunday - Saturday) it should be 0x2. So we should not
be relying on the reset value.

Hence compute the wday using the current date/month/year values.
Check if reset wday is any different from the computed wday,
If different then set the wday which we computed using
date/month/year values.

Document Referred:
http://ww1.microchip.com/downloads/en/DeviceDoc/20002266F.pdf

Fixes: 1d1945d261a2af "drivers/rtc/rtc-ds1307.c: add alarm support for mcp7941x chips"
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
[bwh: Backported to 3.16:
 - No 64-time rtc_time functions available
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index f182dae3a4b751633c0ae3c838cadd2d9d964630..5236842d28aa47f283c93634c785cfb1e709f6a6 100644 (file)
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -611,6 +611,8 @@ static const struct rtc_class_ops ds13xx_rtc_ops = {
  * Alarm support for mcp7941x devices.
  */
 
+#define MCP794XX_REG_WEEKDAY           0x3
+#define MCP794XX_REG_WEEKDAY_WDAY_MASK 0x7
 #define MCP7941X_REG_CONTROL           0x07
 #      define MCP7941X_BIT_ALM0_EN     0x10
 #      define MCP7941X_BIT_ALM1_EN     0x20
@@ -840,12 +842,15 @@ static int ds1307_probe(struct i2c_client *client,
 {
        struct ds1307           *ds1307;
        int                     err = -ENODEV;
-       int                     tmp;
+       int                     tmp, wday;
        const struct chip_desc  *chip = &chips[id->driver_data];
        struct i2c_adapter      *adapter = to_i2c_adapter(client->dev.parent);
        bool                    want_irq = false;
        unsigned char           *buf;
        struct ds1307_platform_data *pdata = dev_get_platdata(&client->dev);
+       struct rtc_time         tm;
+       unsigned long           timestamp;
+
        static const int        bbsqi_bitpos[] = {
                [ds_1337] = 0,
                [ds_1339] = DS1339_BIT_BBSQI,
@@ -1115,6 +1120,27 @@ read_rtc:
                return PTR_ERR(ds1307->rtc);
        }
 
+       /*
+        * Some IPs have weekday reset value = 0x1 which might not correct
+        * hence compute the wday using the current date/month/year values
+        */
+       ds1307_get_time(&client->dev, &tm);
+       wday = tm.tm_wday;
+       rtc_tm_to_time(&tm, &timestamp);
+       rtc_time_to_tm(timestamp, &tm);
+
+       /*
+        * Check if reset wday is different from the computed wday
+        * If different then set the wday which we computed using
+        * timestamp
+        */
+       if (wday != tm.tm_wday) {
+               wday = i2c_smbus_read_byte_data(client, MCP794XX_REG_WEEKDAY);
+               wday = wday & ~MCP794XX_REG_WEEKDAY_WDAY_MASK;
+               wday = wday | (tm.tm_wday + 1);
+               i2c_smbus_write_byte_data(client, MCP794XX_REG_WEEKDAY, wday);
+       }
+
        if (want_irq) {
                err = request_irq(client->irq, ds1307_irq, IRQF_SHARED,
                          ds1307->rtc->name, client);