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

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Message-ID: <081bc734-bfac-1eed-cc2a-c85cd2eac13e@gmail.com>
Date:   Sat, 4 Mar 2023 21:42:22 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
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

Hi Jonathan, all

On 3/4/23 20:35, Jonathan Cameron wrote:
> 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.

Andy asked for that as well. And, while I do not really see the 
usefulness of the namespaces when all symbols are properly prefixed (I 
only see added complexity there) - I agreed to use one.

> 
> 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?

Thanks. I think I'll use that. Although, as all of the symbols are 
prefixed with iio_gts - if I really saw a risk of symbol clash it would 
probably make more sense to use just about anything else ;) This because 
if someone else were prefixing symbols with iio_gts - he would likely be 
using the exactly same namespace.

> 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.

This suits me fine. I have v3 almost prepared - but I'll be very much 
away from the computer next week so it may be the v3 will not be out 
until later. It may be I won't continue work with this until about after 
a week.

Yours,
	-- Matti

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

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