[PATCH] rtc-ds1307: Reset bogus register values on m41t00

[Nate Case <ncase@xes-inc.com>]

On the M41T00, registers are in a random state if the Vbat power
was lost before the driver probes it (regardless of whether or
not the oscillator is still running).  In this case, give all
registers valid values so that the bogus values don't cause it to
error out and skip the device.

Signed-off-by: Nate Case <ncase@xes-inc.com>
---
 drivers/rtc/rtc-ds1307.c |   61 +++++++++++++++++++++++++++++++++++----------
 1 files changed, 47 insertions(+), 14 deletions(-)

diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index 162330b..aec17bb 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -198,6 +198,29 @@ static irqreturn_t ds1307_irq(int irq, void *dev_id)
 
 /*----------------------------------------------------------------------*/
 
+static int ds1307_regs_valid(struct ds1307 *ds1307)
+{
+	int tmp, valid = 1;
+
+	tmp = bcd2bin(ds1307->regs[DS1307_REG_SECS] & 0x7f);
+	if (tmp > 60)
+		valid = 0;
+
+	tmp = bcd2bin(ds1307->regs[DS1307_REG_MIN] & 0x7f);
+	if (tmp > 60)
+		valid = 0;
+
+	tmp = bcd2bin(ds1307->regs[DS1307_REG_MDAY] & 0x3f);
+	if (tmp == 0 || tmp > 31)
+		valid = 0;
+
+	tmp = bcd2bin(ds1307->regs[DS1307_REG_MONTH] & 0x1f);
+	if (tmp == 0 || tmp > 12)
+		valid = 0;
+
+	return valid;
+}
+
 static int ds1307_get_time(struct device *dev, struct rtc_time *t)
 {
 	struct ds1307	*ds1307 = dev_get_drvdata(dev);
@@ -571,6 +594,7 @@ static int __devinit ds1307_probe(struct i2c_client *client,
 	const struct chip_desc	*chip = &chips[id->driver_data];
 	struct i2c_adapter	*adapter = to_i2c_adapter(client->dev.parent);
 	int			want_irq = false;
+	int			already_reset = false;
 
 	if (!i2c_check_functionality(adapter,
 			I2C_FUNC_I2C | I2C_FUNC_SMBUS_WRITE_BYTE_DATA))
@@ -663,6 +687,28 @@ read_rtc:
 	switch (ds1307->type) {
 	case ds_1307:
 	case m41t00:
+		/*
+		 * Registers can be in random state if the Vbat power
+		 * was lost, and sometimes this will happen even with
+		 * the oscillator running.  Give all registers valid
+		 * values so that the bogus values don't cause it to
+		 * error out later on.
+		 */
+		if (!ds1307_regs_valid(ds1307)) {
+			if (already_reset)
+				goto exit_bad;
+			i2c_smbus_write_byte_data(client, DS1307_REG_YEAR, 1);
+			i2c_smbus_write_byte_data(client, DS1307_REG_MONTH, 1);
+			i2c_smbus_write_byte_data(client, DS1307_REG_MDAY, 1);
+			i2c_smbus_write_byte_data(client, DS1307_REG_WDAY, 1);
+			i2c_smbus_write_byte_data(client, DS1307_REG_HOUR, 0);
+			i2c_smbus_write_byte_data(client, DS1307_REG_MIN, 0);
+			i2c_smbus_write_byte_data(client, DS1307_REG_SECS, 1);
+			dev_warn(&client->dev, "reset bogus registers\n");
+			already_reset = true;
+			goto read_rtc;
+		}
+
 		/* clock halted?  turn it on, so clock can tick. */
 		if (tmp & DS1307_BIT_CH) {
 			i2c_smbus_write_byte_data(client, DS1307_REG_SECS, 0);
@@ -707,20 +753,7 @@ read_rtc:
 		break;
 	}
 
-	tmp = ds1307->regs[DS1307_REG_SECS];
-	tmp = bcd2bin(tmp & 0x7f);
-	if (tmp > 60)
-		goto exit_bad;
-	tmp = bcd2bin(ds1307->regs[DS1307_REG_MIN] & 0x7f);
-	if (tmp > 60)
-		goto exit_bad;
-
-	tmp = bcd2bin(ds1307->regs[DS1307_REG_MDAY] & 0x3f);
-	if (tmp == 0 || tmp > 31)
-		goto exit_bad;
-
-	tmp = bcd2bin(ds1307->regs[DS1307_REG_MONTH] & 0x1f);
-	if (tmp == 0 || tmp > 12)
+	if (!ds1307_regs_valid(ds1307))
 		goto exit_bad;
 
 	tmp = ds1307->regs[DS1307_REG_HOUR];
-- 
1.6.0.2