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hwmon: (sht4x) Fix EREMOTEIO errors

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Per datasheet, SHT4x may need up to 8.2ms for a "high repeatability"
measurement to complete.  Attempting to read the result too early
triggers a NAK which then causes an EREMOTEIO error.

This behavior has been confirmed with a logic analyzer while running
the I2C bus at only 40kHz.  The low frequency precludes any
signal-integrity issues, which was also confirmed by the absence of
any CRC8 errors.  In this configuration, a NAK occurred on any read
that followed the measurement command within less than 8.2ms.

Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
Link: https://lore.kernel.org/r/20211120212849.2300854-2-davidm@egauge.net
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
David Mosberger-Tang 2021-11-20 21:28:56 +00:00 committed by Guenter Roeck
parent 214f525255
commit 0e4190d762
1 changed files with 2 additions and 2 deletions
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4
drivers/hwmon/sht4x.c
View file

@ -23,7 +23,7 @@
/*
* I2C command delays (in microseconds)
*/
#define SHT4X_MEAS_DELAY 1000
#define SHT4X_MEAS_DELAY_HPM 8200 /* see t_MEAS,h in datasheet */
#define SHT4X_DELAY_EXTRA 10000
/*
@ -90,7 +90,7 @@ static int sht4x_read_values(struct sht4x_data *data)
if (ret < 0)
goto unlock;
usleep_range(SHT4X_MEAS_DELAY, SHT4X_MEAS_DELAY + SHT4X_DELAY_EXTRA);
usleep_range(SHT4X_MEAS_DELAY_HPM, SHT4X_MEAS_DELAY_HPM + SHT4X_DELAY_EXTRA);
ret = i2c_master_recv(client, raw_data, SHT4X_RESPONSE_LENGTH);
if (ret != SHT4X_RESPONSE_LENGTH) {