linux-kernel - Re: [PATCH v2 1/1] iio: mtk-auxadc: update case IIO_CHAN_INFO

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Date:   Sun, 5 Sep 2021 12:20:17 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Hui Liu <hui.liu@...iatek.com>
Cc:     <robh+dt@...nel.org>, <lars@...afoo.de>, <pmeerw@...erw.net>,
        <srv_heupstream@...iatek.com>, <zhiyong.tao@...iatek.com>,
        <chun-hung.wu@...iatek.com>, <yingjoe.chen@...iatek.com>,
        <seiya.wang@...iatek.com>, <ben.tseng@...iatek.com>,
        <matthias.bgg@...il.com>, <s.hauer@...gutronix.de>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-iio@...r.kernel.org>, <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 1/1] iio: mtk-auxadc: update case
 IIO_CHAN_INFO_PROCESSED

On Tue, 31 Aug 2021 13:42:07 +0800
Hui Liu <hui.liu@...iatek.com> wrote:

> Convert raw data to processed data, the processed data is input voltage.
> 
> Signed-off-by: Hui Liu <hui.liu@...iatek.com>

Looks very much to be a fix. Please track down appropriate patch and let
me know what the Fixes: tag should be.  If you reply to this thread
I'll add it plus a not saying it is an ABI change, but a necessary one
as the driver was previously buggy.

Whilst we are here, what is the cali_data() function actually there for?
Seems to only set *val = *val which is rather pointless.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/mt6577_auxadc.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/iio/adc/mt6577_auxadc.c b/drivers/iio/adc/mt6577_auxadc.c
> index 79c1dd68b909..d4fccd52ef08 100644
> --- a/drivers/iio/adc/mt6577_auxadc.c
> +++ b/drivers/iio/adc/mt6577_auxadc.c
> @@ -82,6 +82,10 @@ static const struct iio_chan_spec mt6577_auxadc_iio_channels[] = {
>  	MT6577_AUXADC_CHANNEL(15),
>  };
>  
> +/* For Voltage calculation */
> +#define VOLTAGE_FULL_RANGE  1500	/* VA voltage */
> +#define AUXADC_PRECISE      4096	/* 12 bits */
> +
>  static int mt_auxadc_get_cali_data(int rawdata, bool enable_cali)
>  {
>  	return rawdata;
> @@ -191,6 +195,10 @@ static int mt6577_auxadc_read_raw(struct iio_dev *indio_dev,
>  		}
>  		if (adc_dev->dev_comp->sample_data_cali)
>  			*val = mt_auxadc_get_cali_data(*val, true);
> +
> +		/* Convert adc raw data to voltage: 0 - 1500 mV */
> +		*val = *val * VOLTAGE_FULL_RANGE / AUXADC_PRECISE;
> +
>  		return IIO_VAL_INT;
>  
>  	default: