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| author | Thomas VanSelus <tvanselus@xes-inc.com> | 2017-12-22 10:51:23 -0600 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-01-09 17:03:57 +0100 |
| commit | 066ed427125eccaab5c0e56cce85d0cff4ee82a4 (patch) | |
| tree | 4ef94b124cc2a03a698407a366c3618a5a6dad3b /drivers/misc/ds1682.c | |
| parent | 2fa065fde217a39987f8931cb800e511fa5178e4 (diff) | |
| download | lwn-066ed427125eccaab5c0e56cce85d0cff4ee82a4.tar.gz lwn-066ed427125eccaab5c0e56cce85d0cff4ee82a4.zip | |
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/ds1682.c')
| -rw-r--r-- | drivers/misc/ds1682.c | 19 |
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 |