misc: ds1682: Ignore update-in-progress ETC reads (066ed427) · Commits · 戴 / test

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>

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

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