[PATCH v3] hwmon: sht3x: wait predefined limits loading complete before access

[PATCH v3] hwmon: sht3x: wait predefined limits loading complete before access

[Emiliano Ingrassia]

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 <ingrassia@epigenesys.com>
---
 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;
-- 
2.15.1

Re: [PATCH v3] hwmon: sht3x: wait predefined limits loading complete before access

[Guenter Roeck]

On Fri, Jan 12, 2018 at 09:42:28PM +0100, Emiliano Ingrassia wrote:
> 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 <ingrassia@epigenesys.com>

Applied.

Thanks,
Guenter

> ---
>  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;
> -- 
> 2.15.1
>