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List:       linux-iio
Subject:    Re: [PATCH] iio: chemical: vz89x hardware i2c workaround
From:       Jonathan Cameron <jic23 () kernel ! org>
Date:       2015-09-27 15:39:07
Message-ID: 56080D9B.9040905 () kernel ! org
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On 23/09/15 05:25, Matt Ranostay wrote:
> Chipset sometime updates in the middle of a reading causing it
> to reset the data pointer, and causing invalid reading of previous data.
> 
> We can check for this invalid state by reading MSB of the resistance
> reading that is always zero, and by also confirming the VOC_short isn't
> zero.
> 
> Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Applied.
> ---
>  drivers/iio/chemical/vz89x.c | 23 +++++++++++++++++++++--
>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/chemical/vz89x.c b/drivers/iio/chemical/vz89x.c
> index b454200..11e59a5 100644
> --- a/drivers/iio/chemical/vz89x.c
> +++ b/drivers/iio/chemical/vz89x.c
> @@ -85,6 +85,21 @@ static const struct attribute_group vz89x_attrs_group = {
>  	.attrs = vz89x_attributes,
>  };
>  
> +/*
> + * Chipset sometime updates in the middle of a reading causing it to reset the
> + * data pointer, and causing invalid reading of previous data.
> + * We can check for this by reading MSB of the resistance reading that is
> + * always zero, and by also confirming the VOC_short isn't zero.
> + */
> +
> +static int vz89x_measurement_is_valid(struct vz89x_data *data)
> +{
> +	if (data->buffer[VZ89X_VOC_SHORT_IDX] == 0)
> +		return 1;
> +
> +	return !!(data->buffer[VZ89X_REG_MEASUREMENT_SIZE - 1] > 0);
> +}
> +
>  static int vz89x_get_measurement(struct vz89x_data *data)
>  {
>  	int ret;
> @@ -106,6 +121,10 @@ static int vz89x_get_measurement(struct vz89x_data *data)
>  		data->buffer[i] = ret;
>  	}
>  
> +	ret = vz89x_measurement_is_valid(data);
> +	if (ret)
> +		return -EAGAIN;
> +
>  	data->last_update = jiffies;
>  
>  	return 0;
> @@ -113,9 +132,9 @@ static int vz89x_get_measurement(struct vz89x_data *data)
>  
>  static int vz89x_get_resistance_reading(struct vz89x_data *data)
>  {
> -	u8 *buf = &data->buffer[VZ89X_VOC_TVOC_IDX];
> +	u8 *buf = &data->buffer[VZ89X_VOC_RESISTANCE_IDX];
>  
> -	return buf[0] | (buf[1] << 8) | (buf[2] << 16);
> +	return buf[0] | (buf[1] << 8);
>  }
>  
>  static int vz89x_read_raw(struct iio_dev *indio_dev,
> 

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