linux-kernel - Re: [PATCH v2 3/4] iio: vcnl4000: Export near level property for proximity sensor

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Message-ID: <20200317120535.GA16807@bogon.m.sigxcpu.org>
Date:   Tue, 17 Mar 2020 13:05:35 +0100
From:   Guido Günther <agx@...xcpu.org>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     Tomas Novotny <tomas@...otny.cz>,
        Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        "Angus Ainslie (Purism)" <angus@...ea.ca>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 3/4] iio: vcnl4000: Export near level property for
 proximity sensor

Hi,
On Mon, Mar 16, 2020 at 07:23:01PM +0100, Lars-Peter Clausen wrote:
> On 3/16/20 6:46 PM, Guido Günther wrote:
> > [...]
> > +static ssize_t vcnl4000_read_near_level(struct iio_dev *indio_dev,
> > +					uintptr_t priv,
> > +					const struct iio_chan_spec *chan,
> > +					char *buf)
> > +{
> > +	struct vcnl4000_data *data = iio_priv(indio_dev);
> > +
> > +	return sprintf(buf, "%u\n", data->near_level);
> > +}
> > +
> > +static const struct iio_chan_spec_ext_info vcnl4000_ext_info[] = {
> > +	{
> > +		.name = "near_level",
> 
> Generally having properties with a underscore in them breaks generic parsing
> of the property name by userspace applications. This is because we use
> underscores to separate different components (type, modifier, etc.) of the
> attribute from each other.
> 
> Do you think calling this "nearlevel" would work?

That works as well. I'll change that for v3.

For my education: Is the type, modifier policy written down somewhere
(similar to
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/leds/leds-class.rst#n44
)?

Cheers,
 -- Guido

> 
> I know there are existing bad examples of properties that use an underscore,
> but we should try to limit introducing new ones.
> 
> > +		.shared = IIO_SEPARATE,
> > +		.read = vcnl4000_read_near_level,
> > +	},
> > +	{ /* sentinel */ }
> > +};
> > +
> >   static const struct iio_chan_spec vcnl4000_channels[] = {
> >   	{
> >   		.type = IIO_LIGHT,
> > @@ -350,6 +371,7 @@ static const struct iio_chan_spec vcnl4000_channels[] = {
> >   	}, {
> >   		.type = IIO_PROXIMITY,
> >   		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> > +		.ext_info = vcnl4000_ext_info,
> >   	}
> >   };
> > @@ -439,6 +461,10 @@ static int vcnl4000_probe(struct i2c_client *client,
> >   	dev_dbg(&client->dev, "%s Ambient light/proximity sensor, Rev: %02x\n",
> >   		data->chip_spec->prod, data->rev);
> > +	if (device_property_read_u32(&client->dev, "near-level",
> > +				     &data->near_level) < 0)
> > +		data->near_level = 0;
> > +
> >   	indio_dev->dev.parent = &client->dev;
> >   	indio_dev->info = &vcnl4000_info;
> >   	indio_dev->channels = vcnl4000_channels;
> 
>