Re: [PATCH v7 4/5] iio: light: ROHM BU27034 Ambient Light Sensor

[Matti Vaittinen]

On 4/8/23 14:21, Jonathan Cameron wrote:
> On Fri, 31 Mar 2023 15:41:58 +0300
> Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
>
> > ROHM BU27034 is an ambient light sensor with 3 channels and 3 photo diodes
> > capable of detecting a very wide range of illuminance. Typical application
> > is adjusting LCD and backlight power of TVs and mobile phones.
> >
> > Add initial  support for the ROHM BU27034 ambient light sensor.
> >
> > NOTE:
> > 	- Driver exposes 4 channels. One IIO_LIGHT channel providing the
> > 	  calculated lux values based on measured data from diodes #0 and
> > 	  #1. In addition, 3 IIO_INTENSITY channels are emitting the raw
> > 	  register data from all diodes for more intense user-space
> > 	  computations.
> > 	- Sensor has GAIN values that can be adjusted from 1x to 4096x.
> > 	- Sensor has adjustible measurement times of 5, 55, 100, 200 and
> > 	  400 mS. Driver does not support 5 mS which has special
> > 	  limitations.
> > 	- Driver exposes standard 'scale' adjustment which is
> > 	  implemented by:
> > 		1) Trying to adjust only the GAIN
> > 		2) If GAIN adjustment alone can't provide requested
> > 		   scale, adjusting both the time and the gain is
> > 		   attempted.
> > 	- Driver exposes writable INT_TIME property that can be used
> > 	  for adjusting the measurement time. Time adjustment will also
> > 	  cause the driver to try to adjust the GAIN so that the
> > 	  overall scale is kept as close to the original as possible.
> >
> > Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>
>
> A few trivial comments inline but nothing that stops me applying this version.
>
> > +static int bu27034_read_raw(struct iio_dev *idev,
> > +			   struct iio_chan_spec const *chan,
> > +			   int *val, int *val2, long mask)
> > +{
> > +	struct bu27034_data *data = iio_priv(idev);
> > +	int ret;
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_INT_TIME:
> > +		*val = bu27034_get_int_time(data);
> > +		if (*val < 0)
> > +			return *val;
> > +
> > +		return IIO_VAL_INT;
> > +
> > +	case IIO_CHAN_INFO_SCALE:
> > +		return bu27034_get_scale(data, chan->channel, val, val2);
> > +
> > +	case IIO_CHAN_INFO_RAW:
> > +	{
> > +		int (*result_get)(struct bu27034_data *data, int chan, int *val);
>
> I don't care that much about this, but the function pointer dance seems
> unnecessary.

My memory is getting worse and worse over the time... It's hard for me 
to remember why I added a function pointer here - but it probably was to 
keep the if-else if-else construct out of the mutex-protected section.

> You could probably also drop the paranoid checking (or default to one of the
> choices).

If this was done, then the function-pointer had no use. If you think the 
check is paranoid, then I agree, we should go with the suggestion you 
have below.

> So at call sight of result_get() currently have
> 		if (chan->type == IIO_INTENSITY)
> 			ret = bu27034_get_single-result()...
> 		else
> 			ret = bu27034_get_mlux()
>
> etc
>
> meh. I didn't raise it earlier so I'll leave this alone.
>
> > +
> > +		if (chan->type == IIO_INTENSITY)
> > +			result_get = bu27034_get_single_result;
> > +		else if (chan->type == IIO_LIGHT)
> > +			result_get = bu27034_get_mlux;
> > +		else
> > +			return -EINVAL;
> > +
> > +		/* Don't mess with measurement enabling while buffering */
> > +		ret = iio_device_claim_direct_mode(idev);
> > +		if (ret)
> > +			return ret;
> > +
> > +		mutex_lock(&data->mutex);
> > +		/*
> > +		 * Reading one channel at a time is inefficient but we
> > +		 * don't care here. Buffered version should be used if
> > +		 * performance is an issue.
> > +		 */
> > +		ret = result_get(data, chan->channel, val);
> > +
> > +		mutex_unlock(&data->mutex);
> > +		iio_device_release_direct_mode(idev);
> > +
> > +		if (ret)
> > +			return ret;
> > +
> > +		return IIO_VAL_INT;
> > +	}
> > +	default:
> > +		return -EINVAL;
> > +
> > +	}
> > +}
>
> I will fix the excess blank line above though.  Serves no purpose
> so gone in the version I applied.

Thanks!

Yours,
	-- Matti

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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