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Commit 066ed427 authored by Thomas VanSelus's avatar Thomas VanSelus Committed by Greg Kroah-Hartman
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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: default avatarThomas VanSelus <tvanselus@xes-inc.com>
Signed-off-by: default avatarAaron Sierra <asierra@xes-inc.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2fa065fd

drivers/misc/ds1682.c

+18 −1
Original line number Diff line number Diff line
@@ -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