linux-kernel - Re: [PATCH 1/1] iio: ak8975: Add Ak8975 magnetometer sensor

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Message-ID: <20100902234124.584b9bf7@lxorguk.ukuu.org.uk>
Date:	Thu, 2 Sep 2010 23:41:24 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Chew <AChew@...dia.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	Laxman Dewangan <ldewangan@...dia.com>
Subject: Re: [PATCH 1/1] iio: ak8975: Add Ak8975 magnetometer sensor

On Thu, 2 Sep 2010 15:16:20 -0700
Andrew Chew <AChew@...dia.com> wrote:

> > > +static IIO_DEVICE_ATTR(mode, S_IRUGO | S_IWUSR, show_mode, 
> > store_mode, 0);
> > > +static IIO_DEVICE_ATTR(magn_x_calibscale, S_IRUGO, 
> > show_calibscale, NULL, 0);
> > > +static IIO_DEVICE_ATTR(magn_y_calibscale, S_IRUGO, 
> > show_calibscale, NULL, 1);
> > > +static IIO_DEVICE_ATTR(magn_z_calibscale, S_IRUGO, 
> > show_calibscale, NULL, 2);
> > > +static IIO_DEV_ATTR_MAGN_X(show_raw, AK8975_REG_HXL);
> > > +static IIO_DEV_ATTR_MAGN_Y(show_raw, AK8975_REG_HYL);
> > > +static IIO_DEV_ATTR_MAGN_Z(show_raw, AK8975_REG_HZL);
> > 
> > This seems odd as an interface as it's raw when the maths to provide
> > non-raw (and thus abstract and easy for user space) data is trivial
> > enough to do in kernel
> 
> IIO guys want to do normalization maths above the kernel-level magnetometer IIO layer.  This interface came before me, so I'm just following current conventions.

That will make a generic IIO <-> input bridge very hard to do right. I
can see why IIO wants to do that but you need both if so and this also
needs discussion.

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