From: Matti Vaittinen <mazziesaccount@gmail.com>
To: Jonathan Cameron <jic23@kernel.org>
Cc: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
Lars-Peter Clausen <lars@metafoo.de>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Paul Gazzillo <paul@pgazz.com>,
Zhigang Shi <Zhigang.Shi@liteon.com>,
Shreeya Patel <shreeya.patel@collabora.com>,
Dmitry Osipenko <dmitry.osipenko@collabora.com>,
linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org
Subject: Re: [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor
Date: Mon, 13 Mar 2023 11:39:06 +0200 [thread overview]
Message-ID: <1b55adf6-32ce-1fd3-78cf-b2011f023eac@gmail.com> (raw)
In-Reply-To: <20230312153655.052d5730@jic23-huawei>
On 3/12/23 17:36, Jonathan Cameron wrote:
> On Sun, 5 Mar 2023 14:22:51 +0200
> Matti Vaittinen <mazziesaccount@gmail.com> wrote:
>
>> On 3/4/23 22:17, Jonathan Cameron wrote:
>>> On Thu, 2 Mar 2023 12:58:59 +0200
>>> Matti Vaittinen <mazziesaccount@gmail.com> wrote:
>>>
// snip
>>>> +static const struct iio_chan_spec bu27034_channels[] = {
>>>> + {
>>>> + .type = IIO_LIGHT,
>>>> + .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
>>>> + BIT(IIO_CHAN_INFO_SCALE),
>>>
>>> What is this scale for?
>>
>> The scale is to inform users that we return data using milli lux.
>>
>>> Given the channel is computed from various different inputs, is there a
>>> clear definition of how it is scaled? What does a write to it mean?
>>
>> Nothing. writing anything else but milli lux scale fails with -EINVAL.
>>
>> I guess I am doing something in an unusual way here :) Do you have a
>> suggestion for me?
>
> Return data in lux?
That's what I did originally have. But then I noticed we can get
slightly better accuracy than that. Hence I switched to mLux and added
the scale.
> Or return it as INFO_RAW - thus making it clear
> that the reading is not in expected units and a conversion must be
> applied by userspace. SCALE is not applied to PROCESSED by userspace.
Ah. This makes sense then. Maybe it would be worth adding a warning to
IIO-core if drivers set both the SCALE and PROCESSED info bits?
So, I need to select between the simplicity or better accuracy here? :/
I really hate ending up making choices like this without knowing all the
real use-cases :( And it happens a lot for me. Well, I guess I'll drop
the scale, use luxes and go with the PROCESSED data. My understanding is
that the "thing" with the sensor is a wide-range for wavelengths, not
the accuracy. So, maybe luxes are just good enough - and again, users
needing something more accurate can utilize the raw intensity channels.
>
> In the rare case where you do get SCALE and PROCESSED it's there to allow
> for changes in the underlying signal measurement that are eaten up in the
> computation needed to get to PROCESSED - that is they have no visible
> affect (beyond range changes etc).
Oh, Ok. So there is a valid case for setting both SCALE and PROCESSED.
Then we can't add teh warning I assume :(
Yours,
-- Matti
--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
next prev parent reply other threads:[~2023-03-13 9:40 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-02 10:57 [PATCH v2 0/6] Support ROHM BU27034 ALS sensor Matti Vaittinen
2023-03-02 10:57 ` [PATCH v2 1/6] dt-bindings: iio: light: Support ROHM BU27034 Matti Vaittinen
2023-03-02 10:57 ` [PATCH v2 2/6] iio: light: Add gain-time-scale helpers Matti Vaittinen
2023-03-02 15:05 ` Andy Shevchenko
2023-03-03 7:54 ` Vaittinen, Matti
2023-03-06 11:13 ` Andy Shevchenko
2023-03-13 11:31 ` Matti Vaittinen
2023-03-13 14:39 ` Andy Shevchenko
2023-03-14 10:28 ` Matti Vaittinen
2023-03-14 11:31 ` Andy Shevchenko
2023-03-14 11:36 ` Andy Shevchenko
2023-03-15 7:20 ` Vaittinen, Matti
2023-03-18 16:49 ` Jonathan Cameron
2023-03-04 18:35 ` Jonathan Cameron
2023-03-04 19:42 ` Matti Vaittinen
2023-03-06 11:15 ` Andy Shevchenko
2023-03-02 10:58 ` [PATCH v2 3/6] iio: test: test " Matti Vaittinen
2023-03-02 10:58 ` [PATCH v2 4/6] MAINTAINERS: Add IIO " Matti Vaittinen
2023-03-02 10:58 ` [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor Matti Vaittinen
2023-03-02 14:17 ` Matti Vaittinen
2023-03-02 15:34 ` Andy Shevchenko
2023-03-03 9:17 ` Matti Vaittinen
2023-03-04 19:02 ` Jonathan Cameron
2023-03-04 20:28 ` Matti Vaittinen
2023-03-04 20:17 ` Jonathan Cameron
2023-03-05 12:22 ` Matti Vaittinen
2023-03-12 15:36 ` Jonathan Cameron
2023-03-13 9:39 ` Matti Vaittinen [this message]
2023-03-18 16:54 ` Jonathan Cameron
2023-03-19 15:59 ` Matti Vaittinen
2023-03-14 9:39 ` Matti Vaittinen
2023-03-18 16:57 ` Jonathan Cameron
2023-03-05 13:10 ` Matti Vaittinen
2023-03-06 11:21 ` Andy Shevchenko
2023-03-13 8:54 ` Matti Vaittinen
2023-03-02 10:59 ` [PATCH v2 6/6] MAINTAINERS: Add ROHM BU27034 Matti Vaittinen
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