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authorThomas VanSelus <tvanselus@xes-inc.com>2017-12-22 10:51:23 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-01-09 17:03:57 +0100
commit066ed427125eccaab5c0e56cce85d0cff4ee82a4 (patch)
tree4ef94b124cc2a03a698407a366c3618a5a6dad3b /drivers/misc
parent2fa065fde217a39987f8931cb800e511fa5178e4 (diff)
misc: ds1682: Ignore update-in-progress ETC reads
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 <tvanselus@xes-inc.com> Signed-off-by: Aaron Sierra <asierra@xes-inc.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/misc')
-rw-r--r--drivers/misc/ds1682.c19
1 files changed, 18 insertions, 1 deletions
diff --git a/drivers/misc/ds1682.c b/drivers/misc/ds1682.c
index 0fc5366457b9..98a921ea9ee8 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

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