From abe6c3b06fa80777e321add05345c799a74e624a Mon Sep 17 00:00:00 2001 From: Emiliano Ingrassia Date: Fri, 12 Jan 2018 21:42:28 +0100 Subject: [PATCH] hwmon: (sht3x) wait predefined limits loading complete before access An sht3x sensor include limits register which contains temperature and humidity limit values. After a reset, pre-defined values are loaded into that register. During the probe function, the driver reads the limits register. However, if the reads are made too early, and the bus is clocked at high frequencies (e.g. 100 kHz or more), the loading could be not completed and the sensor returns a NACK which causes the probe to fail. A delay of at least 500 us before the first read solves this issue. Signed-off-by: Emiliano Ingrassia Signed-off-by: Guenter Roeck --- drivers/hwmon/sht3x.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/hwmon/sht3x.c b/drivers/hwmon/sht3x.c index 6ea99cd6ae79..370b57dafab7 100644 --- a/drivers/hwmon/sht3x.c +++ b/drivers/hwmon/sht3x.c @@ -732,6 +732,13 @@ static int sht3x_probe(struct i2c_client *client, mutex_init(&data->i2c_lock); mutex_init(&data->data_lock); + /* + * An attempt to read limits register too early + * causes a NACK response from the chip. + * Waiting for an empirical delay of 500 us solves the issue. + */ + usleep_range(500, 600); + ret = limits_update(data); if (ret) return ret;