linux-kernel - Re: [PATCH 2/2] iio: bu27034: Add a read only HWARDWAREGAIN

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Date: Sat, 15 Jun 2024 18:50:36 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>, Lars-Peter Clausen
 <lars@...afoo.de>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: bu27034: Add a read only HWARDWAREGAIN

On Mon, 10 Jun 2024 13:01:40 +0300
Matti Vaittinen <mazziesaccount@...il.com> wrote:

> The ROHM BU27034 light sensor has two data channels for measuring
> different frequencies of light. The result from these channels is
> combined into Lux value while the raw channel values are reported via
> intensity channels.
> 
> Both of the intensity channels have adjustable gain setting which
> impacts the scale of the raw channels. Eg, doubling the gain will double
> the values read from the raw channels, which halves the scale value. The
> integration time can also be set for the sensor. This does also have an
> impact to the scale of the intensity channels because increasing the
> integration time will also increase the values reported via the raw
> channels.
> 
> Impact of integration time to the scale and the fact that the scale value
> does not start from '1', can make it hard for a human reader to compute the
> gain values based on the scale.
> 
> Add read-only HARDWAREGAIN to help debugging.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
Other than the thing the bot found with fallthrough on the switch statement
not being marked LGTM.
> ---
>  drivers/iio/light/rohm-bu27034.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/light/rohm-bu27034.c b/drivers/iio/light/rohm-bu27034.c
> index 51acad2cafbd..b299ff2aacce 100644
> --- a/drivers/iio/light/rohm-bu27034.c
> +++ b/drivers/iio/light/rohm-bu27034.c
> @@ -149,7 +149,8 @@ static const struct iio_itime_sel_mul bu27034_itimes[] = {
>  	.channel = BU27034_CHAN_##_name,				\
>  	.channel2 = IIO_MOD_LIGHT_CLEAR,				\
>  	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |			\
> -			      BIT(IIO_CHAN_INFO_SCALE),			\
> +			      BIT(IIO_CHAN_INFO_SCALE) |		\
> +			      BIT(IIO_CHAN_INFO_HARDWAREGAIN),		\
>  	.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),	\
>  	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_INT_TIME),		\
>  	.info_mask_shared_by_all_available =				\
> @@ -992,6 +993,13 @@ static int bu27034_read_raw(struct iio_dev *idev,
>  
>  		return IIO_VAL_INT_PLUS_MICRO;
>  
> +	case IIO_CHAN_INFO_HARDWAREGAIN:
> +		ret = bu27034_get_gain(data, chan->channel, val);
> +		if (ret)
> +			return ret;
> +
> +		return IIO_VAL_INT;
> +
>  	case IIO_CHAN_INFO_SCALE:
>  		return bu27034_get_scale(data, chan->channel, val, val2);
>  
> @@ -1036,12 +1044,16 @@ static int bu27034_write_raw_get_fmt(struct iio_dev *indio_dev,
>  				     struct iio_chan_spec const *chan,
>  				     long mask)
>  {
> +	struct bu27034_data *data = iio_priv(indio_dev);
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_SCALE:
>  		return IIO_VAL_INT_PLUS_NANO;
>  	case IIO_CHAN_INFO_INT_TIME:
>  		return IIO_VAL_INT_PLUS_MICRO;
> +	case IIO_CHAN_INFO_HARDWAREGAIN:
> +		dev_dbg(data->dev,
> +			"HARDWAREGAIN is read-only, use scale to set\n");

return -EINVAL here.  You could use a fall through marking but it gains
little so I wouldn't bother.

>  	default:
>  		return -EINVAL;
>  	}