linux-kernel - Re: [PATCH v4 2/2] iio: hx711: fix bug in reset functionality

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Date:   Sun, 17 Dec 2017 12:45:08 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andreas Klinger <ak@...klinger.de>
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        singhalsimran0@...il.com, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] iio: hx711: fix bug in reset functionality

On Wed, 13 Dec 2017 18:10:34 +0100
Andreas Klinger <ak@...klinger.de> wrote:

> Return value in hx711_reset() should indicate status of dout otherwise the
> calling function is reporting an error as false positive
> 
> If there are two reads too close to each other, then the second one will
> never succeed. This happens especially when using buffered mode with both
> channels enabled.
> 
> When changing the channel on every trigger event the former 100 ms are not
> enough for waiting until the device indicates normal mode.
> 
> Wait up to 1 second until the device turns into normal mode.
> 
> Signed-off-by: Andreas Klinger <ak@...klinger.de>
An unrelated cleanup snuck in here, but as it's so trivial I'll let it go.

Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/hx711.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
> index a38162ee7dcb..9430b54121e0 100644
> --- a/drivers/iio/adc/hx711.c
> +++ b/drivers/iio/adc/hx711.c
> @@ -153,15 +153,16 @@ static int hx711_wait_for_ready(struct hx711_data *hx711_data)
>  	int i, val;
>  
>  	/*
> -	 * a maximum reset cycle time of 56 ms was measured.
> -	 * we round it up to 100 ms
> +	 * in some rare cases the reset takes quite a long time
> +	 * especially when the channel is changed.
> +	 * Allow up to one second for it
>  	 */
>  	for (i = 0; i < 100; i++) {
>  		val = gpiod_get_value(hx711_data->gpiod_dout);
>  		if (!val)
>  			break;
> -		/* sleep at least 1 ms */
> -		msleep(1);
> +		/* sleep at least 10 ms */
> +		msleep(10);
>  	}
>  	if (val)
>  		return -EIO;
> @@ -203,9 +204,7 @@ static int hx711_reset(struct hx711_data *hx711_data)
>  		 * after a dummy read we need to wait vor readiness
>  		 * for not mixing gain pulses with the clock
>  		 */
> -		ret = hx711_wait_for_ready(hx711_data);
> -		if (ret)
> -			return ret;
> +		val = hx711_wait_for_ready(hx711_data);

This is technically an unrelated change and shouldn't
be in this patch.

>  	}
>  
>  	return val;