linux-kernel - Re: [PATCH v2] iio: humidity: hdc100x: Add margin to the conversion time

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Message-ID: <CAHp75VdBHdqFDqnZc2Ow2Muc_fHk_PZuSqEXMJcxJE6_YEL8gw@mail.gmail.com>
Date:   Thu, 10 Jun 2021 16:55:20 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Chris Lesiak <chris.lesiak@...or.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iio: humidity: hdc100x: Add margin to the conversion time

On Thu, Jun 10, 2021 at 4:47 PM 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.

This is crucial and not so visible in the code, see below.

> Fixes: 4839367d99e3 ("iio: humidity: add HDC100x support")
> Signed-off-by: Chris Lesiak <chris.lesiak@...or.com>
> ---
>  drivers/iio/humidity/hdc100x.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/humidity/hdc100x.c b/drivers/iio/humidity/hdc100x.c
> index 2a957f19048e..91790aa8beeb 100644
> --- a/drivers/iio/humidity/hdc100x.c
> +++ b/drivers/iio/humidity/hdc100x.c
> @@ -166,7 +166,7 @@ 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] + 1000;

+ 1 * USEC_PER_MSEC;

>         int ret;
>         __be16 val;
>
> @@ -316,7 +316,7 @@ 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] + 2000;

+ 2 * USEC_PER_MSEC

>         int ret;
>
>         /* dual read starts at temp register */

Above might require to add #include <vdso/time64.h>.

-- 
With Best Regards,
Andy Shevchenko