From: Thomas VanSelus <[email protected]>
The Elapsed Time Counter (ETC) registers are not buffered for reading.
If a 250ms tick occurs while data is being read out, the result can be
a combination of old and new values. This can occur at the byte level
(giving a time in the future) or the individual bit level (giving a
time in the past). We catch both these cases by reading until we get
two equal or consecutive values. After five unsuccessful attempts we
give up.
Signed-off-by: Thomas VanSelus <[email protected]>
Signed-off-by: Aaron Sierra <[email protected]>
---
drivers/misc/ds1682.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/drivers/misc/ds1682.c b/drivers/misc/ds1682.c
index 0fc5366..98a921e 100644
--- a/drivers/misc/ds1682.c
+++ b/drivers/misc/ds1682.c
@@ -59,7 +59,7 @@ static ssize_t ds1682_show(struct device *dev, struct device_attribute *attr,
{
struct sensor_device_attribute_2 *sattr = to_sensor_dev_attr_2(attr);
struct i2c_client *client = to_i2c_client(dev);
- unsigned long long val;
+ unsigned long long val, check;
__le32 val_le = 0;
int rc;
@@ -73,6 +73,23 @@ static ssize_t ds1682_show(struct device *dev, struct device_attribute *attr,
val = le32_to_cpu(val_le);
+ if (sattr->index == DS1682_REG_ELAPSED) {
+ int retries = 5;
+
+ /* Detect and retry when a tick occurs mid-read */
+ do {
+ rc = i2c_smbus_read_i2c_block_data(client, sattr->index,
+ sattr->nr,
+ (u8 *)&val_le);
+ if (rc < 0 || retries <= 0)
+ return -EIO;
+
+ check = val;
+ val = le32_to_cpu(val_le);
+ retries--;
+ } while (val != check && val != (check + 1));
+ }
+
/* Format the output string and return # of bytes
* Special case: the 32 bit regs are time values with 1/4s
* resolution, scale them up to milliseconds
--
2.7.4