linux-kernel - Re: [PATCH v9 8/8] iio: adc: ad4851: add ad485x driver

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Message-ID: <20250117154309.000003e1@huawei.com>
Date: Fri, 17 Jan 2025 15:43:09 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Uwe Kleine-König <u.kleine-koenig@...libre.com>
CC: Antoniu Miclaus <antoniu.miclaus@...log.com>, <jic23@...nel.org>,
	<robh@...nel.org>, <conor+dt@...nel.org>, <linux-iio@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-pwm@...r.kernel.org>
Subject: Re: [PATCH v9 8/8] iio: adc: ad4851: add ad485x driver

On Fri, 17 Jan 2025 10:59:04 +0100
Uwe Kleine-König <u.kleine-koenig@...libre.com> wrote:

> Hello,
> 
> On Fri, Dec 20, 2024 at 02:01:34PM +0200, Antoniu Miclaus wrote:
> > +static const int ad4851_oversampling_ratios[] = {
> > +	1, 2, 4, 8, 16,	32, 64, 128,
> > +	256, 512, 1024, 2048, 4096, 8192, 16384, 32768,
> > +	65536,
> > +};
> > +
> > +static int ad4851_osr_to_regval(unsigned int ratio)
> > +{
> > +	int i;
> > +
> > +	for (i = 1; i < ARRAY_SIZE(ad4851_oversampling_ratios); i++)
> > +		if (ratio == ad4851_oversampling_ratios[i])
> > +			return i - 1;
> > +
> > +	return -EINVAL;
> > +}  
> 
> This can be simplified (I guess) using something like:
> 
> 	if (ratio >= 2 && ratio <= 65536 && is_power_of_2(ratio))
> 		return ilog2(ratio) - 1;
> 
> 	return -EINVAL;
Hi Uwe,

Only at the cost of providing custom handling to compute the above
array in order to provide it to userspace via the read_avail() callback.

We could do what you have here and provide the array but that would
be less clear than just looking it up.

> 
> > +static void __ad4851_get_scale(struct iio_dev *indio_dev, int scale_tbl,
> > +			       unsigned int *val, unsigned int *val2)
> > +{
> > [...]
> > +}
> > +
> > +static int ad4851_scale_fill(struct iio_dev *indio_dev)
> > +{
> > [...]
> > +}
> > +
> > +static int ad4851_set_oversampling_ratio(struct iio_dev *indio_dev,
> > +					 const struct iio_chan_spec *chan,
> > +					 unsigned int osr)
> > +{
> > [...]
> > +}
> > +
> > +static int ad4851_get_oversampling_ratio(struct ad4851_state *st, unsigned int *val)
> > +{
> > +	unsigned int osr;
> > +	int ret;
> > +
> > +	guard(mutex)(&st->lock);
> > +
> > +	ret = regmap_read(st->regmap, AD4851_REG_OVERSAMPLE, &osr);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (!FIELD_GET(AD4851_OS_EN_MSK, osr))
> > +		*val = 1;
> > +	else
> > +		*val = ad4851_oversampling_ratios[FIELD_GET(AD4851_OS_RATIO_MSK, osr) + 1];  
> 
> With the suggestion above this gets:
> 
> 	*val = 2 << FIELD_GET(AD4851_OS_RATIO_MSK, osr);
> 
> (or 
> 	*val = 1 << (FIELD_GET(AD4851_OS_RATIO_MSK, osr) + 1);
> 
> ). Then you can drop ad4851_oversampling_ratios[].
You missed the usage in as4851_read_avail() which is the reason it exists.
These others are just convenient given that it already exists.

Jonathan


> 
> > +
> > +	st->osr = *val;
> > +
> > +	return IIO_VAL_INT;
> > +}  
> 
> Best regards
> Uwe
>