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

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Date:   Mon, 10 Apr 2023 13:38:16 +0300
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Paul Gazzillo <paul@...zz.com>,
        Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Shreeya Patel <shreeya.patel@...labora.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH v7 4/5] iio: light: ROHM BU27034 Ambient Light Sensor

On 4/8/23 14:21, Jonathan Cameron wrote:
> On Fri, 31 Mar 2023 15:41:58 +0300
> Matti Vaittinen <mazziesaccount@...il.com> 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@...il.com>
> 
> 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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