linux-kernel - Re: [PATCH v2 2/6] iio: light: Add gain-time-scale helpers

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Date:   Sat, 4 Mar 2023 18:35:57 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Matti Vaittinen <mazziesaccount@...il.com>
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>,
        Zhigang Shi <Zhigang.Shi@...eon.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH v2 2/6] iio: light: Add gain-time-scale helpers

On Thu, 2 Mar 2023 12:57:54 +0200
Matti Vaittinen <mazziesaccount@...il.com> 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.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>

Probably makes sense to put the exports in their own namespace.

I've been meaning to finish namespacing the rest of IIO but not
gotten around to it yet.
As this is a separate library probably makes sense to have a unique
namespace for it that the users opt in on.
Perhaps IIO_GTS makes sense?

Otherwise, as Andy's done a detailed review of this version I'll let
you update it for those comments and take another look at v3.

Thanks,

Jonathan