rtc: ds1347: properly handle oscillator failures

The comment in the probe function stating that it disables oscillator stop
detection and glitch filtering is incorrect as it sets bits 3 and 4 while
it should be setting 5 and 6 to achieve that. Then, it is safe to assume
that the oscillator failure detection is actually enabled.

Properly handle oscillator failures by returning -EINVAL when the time and
date are know to be incorrect and reset the flag when the time is set.

Link: https://lore.kernel.org/r/20191007134724.15505-8-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

1 files changed, 23 insertions, 7 deletions

diff --git a/drivers/rtc/rtc-ds1347.c b/drivers/rtc/rtc-ds1347.c
index 22a75b01f1ac4..eeaf43586bce7 100644
--- a/drivers/rtc/rtc-ds1347.c
+++ b/drivers/rtc/rtc-ds1347.c
@@ -29,6 +29,9 @@
 #define DS1347_STATUS_REG	0x17
 #define DS1347_CLOCK_BURST	0x3F
 
+#define DS1347_NEOSC_BIT	BIT(7)
+#define DS1347_OSF_BIT		BIT(2)
+
 static const struct regmap_range ds1347_ranges[] = {
 	{
 		.range_min = DS1347_SECONDS_REG,
@@ -44,9 +47,17 @@ static const struct regmap_access_table ds1347_access_table = {
 static int ds1347_read_time(struct device *dev, struct rtc_time *dt)
 {
 	struct regmap *map = dev_get_drvdata(dev);
+	unsigned int status;
 	int err;
 	unsigned char buf[8];
 
+	err = regmap_read(map, DS1347_STATUS_REG, &status);
+	if (err)
+		return err;
+
+	if (status & DS1347_OSF_BIT)
+		return -EINVAL;
+
 	err = regmap_bulk_read(map, DS1347_CLOCK_BURST, buf, 8);
 	if (err)
 		return err;
@@ -66,6 +77,12 @@ static int ds1347_set_time(struct device *dev, struct rtc_time *dt)
 {
 	struct regmap *map = dev_get_drvdata(dev);
 	unsigned char buf[8];
+	int err;
+
+	err = regmap_update_bits(map, DS1347_STATUS_REG,
+				 DS1347_NEOSC_BIT, DS1347_NEOSC_BIT);
+	if (err)
+		return err;
 
 	buf[0] = bin2bcd(dt->tm_sec);
 	buf[1] = bin2bcd(dt->tm_min);
@@ -82,7 +99,12 @@ static int ds1347_set_time(struct device *dev, struct rtc_time *dt)
 	buf[7] = bin2bcd(0x00);
 
 	/* write the rtc settings */
-	return regmap_bulk_write(map, DS1347_CLOCK_BURST, buf, 8);
+	err = regmap_bulk_write(map, DS1347_CLOCK_BURST, buf, 8);
+	if (err)
+		return err;
+
+	return regmap_update_bits(map, DS1347_STATUS_REG,
+				  DS1347_NEOSC_BIT | DS1347_OSF_BIT, 0);
 }
 
 static const struct rtc_class_ops ds1347_rtc_ops = {
@@ -123,12 +145,6 @@ static int ds1347_probe(struct spi_device *spi)
 	data = data & ~(1<<7);
 	regmap_write(map, DS1347_CONTROL_REG, data);
 
-	/* Enable the oscillator , disable the oscillator stop flag,
-	 and glitch filter to reduce current consumption */
-	regmap_read(map, DS1347_STATUS_REG, &data);
-	data = data & 0x1B;
-	regmap_write(map, DS1347_STATUS_REG, data);
-
 	rtc = devm_rtc_allocate_device(&spi->dev);
 	if (IS_ERR(rtc))
 		return PTR_ERR(rtc);