Re: [PATCH v3 2/6] iio: light: Add gain-time-scale helpers

[Matti Vaittinen]

On 3/12/23 18:51, Jonathan Cameron wrote:
> On Mon, 6 Mar 2023 14:52:57 +0200
> Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> > On Mon, Mar 06, 2023 at 11:17:15AM +0200, Matti Vaittinen wrote:
> > > Some light sensors can adjust both the HW-gain and integration time.
> > > There are cases where adjusting the integration time has similar impact
> > > to the scale of the reported values as gain setting has.
> > >
> > > IIO users do typically expect to handle scale by a single writable 'scale'
> > > entry. Driver should then adjust the gain/time accordingly.
> > >
> > > It however is difficult for a driver to know whether it should change
> > > gain or integration time to meet the requested scale. Usually it is
> > > preferred to have longer integration time which usually improves
> > > accuracy, but there may be use-cases where long measurement times can be
> > > an issue. Thus it can be preferable to allow also changing the
> > > integration time - but mitigate the scale impact by also changing the gain
> > > underneath. Eg, if integration time change doubles the measured values,
> > > the driver can reduce the HW-gain to half.
> > >
> > > The theory of the computations of gain-time-scale is simple. However,
> > > some people (undersigned) got that implemented wrong for more than once.
> > >
> > > Add some gain-time-scale helpers in order to not dublicate errors in all
> > > drivers needing these computations.
> >
> > ...
> >
> > > +/*
> >
> > If it's deliberately not a kernel doc, why to bother to have it looking as one?
> > It's really a provocative to some people who will come with a patches to "fix"
> > this...
>
> Just make it kernel-doc.

Are you sure...? I don't like the idea of polluting generated docs with 
documentation for this type of tiny internal pieces not usable outside 
this component anyways...

> > > + * iio_gts_get_gain - Convert scale to total gain
> > > + *
> > > + * Internal helper for converting scale to total gain.
> > > + *
> > > + * @max:	Maximum linearized scale. As an example, when scale is created
> > > + *		in magnitude of NANOs and max scale is 64.1 - The linearized
> > > + *		scale is 64 100 000 000.
> > > + * @scale:	Linearized scale to compte the gain for.
> > > + *
> > > + * Return:	(floored) gain corresponding to the scale. -EINVAL if scale
> > > + *		is invalid.
> > > + */
>
> > ...
> >
> > > +EXPORT_SYMBOL_NS_GPL(iio_gts_total_gain_to_scale, IIO_GTS_HELPER);
> >
> > I would say _HELPER part is too much, but fine with me.
>
> Hmm. I think I like the HELPER bit as separates it from being a driver.
> Of course I might change my mind after a few sleeps.

Ever considered a career as a politician? ;) (No offense intended - and 
feel free to change your mind on this. I don't expect this to be done 
tomorrow)

> > > +++ b/drivers/iio/light/iio-gts-helper.h
> >
> > Is it _only_ for a Light type of sensors?
>
> I'd move it up a directory and allow for other users.

Ok. I'll do the move for the next version.

Yours,
	-- Matti

> Jonathan

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

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