linux-kernel - Re: [PATCH v3] iio: humidity: hdc100x: Add margin to the conversion time

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Date:   Wed, 16 Jun 2021 13:43:35 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Chris Lesiak <chris.lesiak@...or.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matt Ranostay <matt.ranostay@...sulko.com>
Subject: Re: [PATCH v3] iio: humidity: hdc100x: Add margin to the conversion
 time

On Mon, 14 Jun 2021 09:18:20 -0500
Chris Lesiak <chris.lesiak@...or.com> wrote:

> The datasheets have the following note for the conversion time
> specification: "This parameter is specified by design and/or
> characterization and it is not tested in production."
> 
> Parts have been seen that require more time to do 14-bit conversions for
> the relative humidity channel.  The result is ENXIO due to the address
> phase of a transfer not getting an ACK.
> 
> Delay an additional 1 ms per conversion to allow for additional margin.
> 
> Fixes: 4839367d99e3 ("iio: humidity: add HDC100x support")
> Signed-off-by: Chris Lesiak <chris.lesiak@...or.com>

+CC Matt as this is one of his drivers.

Looks good to me.

> ---
>  drivers/iio/humidity/hdc100x.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/humidity/hdc100x.c b/drivers/iio/humidity/hdc100x.c
> index 2a957f19048e..9e0fce917ce4 100644
> --- a/drivers/iio/humidity/hdc100x.c
> +++ b/drivers/iio/humidity/hdc100x.c
> @@ -25,6 +25,8 @@
>  #include <linux/iio/trigger_consumer.h>
>  #include <linux/iio/triggered_buffer.h>
>  
> +#include <linux/time.h>
> +
>  #define HDC100X_REG_TEMP			0x00
>  #define HDC100X_REG_HUMIDITY			0x01
>  
> @@ -166,7 +168,7 @@ static int hdc100x_get_measurement(struct hdc100x_data *data,
>  				   struct iio_chan_spec const *chan)
>  {
>  	struct i2c_client *client = data->client;
> -	int delay = data->adc_int_us[chan->address];
> +	int delay = data->adc_int_us[chan->address] + 1*USEC_PER_MSEC;
>  	int ret;
>  	__be16 val;
>  
> @@ -316,7 +318,7 @@ static irqreturn_t hdc100x_trigger_handler(int irq, void *p)
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	struct hdc100x_data *data = iio_priv(indio_dev);
>  	struct i2c_client *client = data->client;
> -	int delay = data->adc_int_us[0] + data->adc_int_us[1];
> +	int delay = data->adc_int_us[0] + data->adc_int_us[1] + 2*USEC_PER_MSEC;
>  	int ret;
>  
>  	/* dual read starts at temp register */