Commit 0e4190d7 authored by David Mosberger-Tang's avatar David Mosberger-Tang Committed by Guenter Roeck
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hwmon: (sht4x) Fix EREMOTEIO errors 



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: default avatarDavid Mosberger-Tang <davidm@egauge.net>
Link: https://lore.kernel.org/r/20211120212849.2300854-2-davidm@egauge.net


Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent 214f5252

drivers/hwmon/sht4x.c

+2 −2
Original line number Diff line number Diff line
@@ -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) {