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Message-ID: <2a15c359-2a04-9a45-f30a-c7a0e4b67871@axentia.se>
Date:   Tue, 17 Oct 2023 16:00:22 +0200
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Subject: Re: [PATCH v2] iio: afe: rescale: Accept only offset channels
Content-Language: sv-SE
To:     Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Liam Beguin <liambeguin@gmail.com>, linux-iio@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230902-iio-rescale-only-offset-v2-1-988b807754c8@linaro.org>
 <a0a55276-297b-e2b7-79b3-e4aadd39b400@axentia.se>
 <CACRpkdaMj2XFcwqaSiRSA2A41zYsW=AG_Fi7v7AjbuLBByxVaQ@mail.gmail.com>
 <948548a0-d132-4f5c-819e-40bacb367be4@axentia.se>
 <20231017100539.000039b0@Huawei.com>
From:   Peter Rosin <peda@axentia.se>
In-Reply-To: <20231017100539.000039b0@Huawei.com>
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Hi!

2023-10-17 at 11:05, Jonathan Cameron wrote:
> On Mon, 16 Oct 2023 12:05:32 +0200
> Peter Rosin <peda@axentia.se> wrote:
>> 2023-10-16 at 10:39, Linus Walleij wrote:


>>> Just raw (with neither offset or rescale) doesn't make sense, since  
>>
>> And I don't see why not. That's the crux.
>>
>>> the AFE rescaler does just offsetting and rescaling, in that case the
>>> user should just use the raw channel. Also it would then take
>>> precedence over a processed channel (which applies rescale and
>>> offset internally) which doesn't make sense to me.  
>>
>> Why isn't it perfectly fine for a device to provide only a raw
>> channel and then expect that to be interpreted as the real unit?
>> Why would it need a processed channel when no processing is
>> going on? E.g. a device reporting the temp in the expected unit
>> in one of its registers. Or whatever with such a friendly
>> register.
> 
> In that case it should report a processed value to indicate that.
> It's admittedly a bit of a corner case given it's not processed by
> the kernel - there is an argument that this (more or less) only
> happens when someone has processed a raw ADC count but in theory
> that's not necessarily true.
> 
> There are a few examples of drivers passing through the register value
> as processed in tree - normally when there
> is a microprocessor doing some fusion of signals or similar.
> 
> Raw gets reported on it's own in a few other cases, such as when
> there are no known units - that happens for things like light intensity,
> proximity (which is often reflected light intensity).
> For those I'm not sure the rescaler is useful.

Excellent, thanks for the clarification!

Reviewed-by: Peter Rosin <peda@axentia.se>

Cheers,
Peter