linux-kernel - Re: [PATCH v5 5/8] iio: test: test gain-time-scale helpers

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Date:   Fri, 24 Mar 2023 08:29:44 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Liam Beguin <liambeguin@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        Stephen Boyd <sboyd@...nel.org>,
        Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH v5 5/8] iio: test: test gain-time-scale helpers

On 3/22/23 11:07, 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.
> Hence some gain-time-scale helpers were introduced.
> 
> Add some simple tests to verify the most hairy functions.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> 
> ---
> Changes:
> v4 => v5:
> - remove empty lines from Kconfig
> - adapt to drop of the non devm iio_init

I think you may want to skip reviewing this specific patch. After having 
a chat with Greg, David, and Maxime it seems this will be changed quite 
a bit for v6.

Most notably, I am planning to drop the generic helpers and struct 
gts_test. I'll also simplify the signatures of 
__test_init_iio_gain_scale() and test_init_iio_gain_scale().

Yours,
	-- Matti

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

~~ When things go utterly wrong vim users can always type :help! ~~