linux-kernel - Re: [PATCH v1 0/3] iio: afe: rescale: Add INFO

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Date:   Tue, 11 Jun 2019 11:02:14 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Mylène Josserand <mylene.josserand@...tlin.com>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "knaack.h@....de" <knaack.h@....de>,
        "lars@...afoo.de" <lars@...afoo.de>,
        "pmeerw@...erw.net" <pmeerw@...erw.net>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>
CC:     "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v1 0/3] iio: afe: rescale: Add INFO_PROCESSED support

On 2019-06-11 11:56, Mylène Josserand wrote:
> Hello everyone,
> 
> You will find a small series that add the support of processed values
> for iio-rescale driver.
> Thanks to that, it is possible to read processed values in sysfs instead
> of getting only raw and scale values.
> 
> Here is an example for a 3v3 voltage reading:
> # cat /sys/bus/iio/devices/iio\:device1/in_voltage0_scale
> 3.791015625
> # cat /sys/bus/iio/devices/iio\:device1/in_voltage0_raw
> 879
> # cat /sys/bus/iio/devices/iio\:device1/in_voltage0_input
> 3332
> 
> It is also possible to read directly the processed values using iio-hwmon
> driver (see example in patch03):
> 
> # cat /sys/class/hwmon/hwmon0/in1_input
> 3328
> 
> I seperated my series in 3 patches:
>    - Patch01: Move the scale conversion into a function to prepare the
>    support of IIO_CHAN_INFO_PROCESSED.
>    - Patch02: Add the support of IIO_CHAN_INFO_PROCESSED.
>    - Patch03: Add an example of the use of hwmon and voltage-divider nodes
>    in device-tree.
> 
> If you have any feedbacks on it, I will be pleased to read them!


The last patch about hwmon has nothing to do with this series, and
should be possible as-is without any code changes. No? AFAICT,
iio_hwmon calls iio_read_channel_processed, which calls
iio_convert_raw_to_processed_unlocked in case IIO_CHAN_INFO_PROCESSES
is not handled by the driver. Is that not working?

There is also libiio in userspace that provides the scale as a double
and makes the conversion to a processed value trivial, so the series
is really mostly about the convenience of having a human directly
seeing the processed value in sysfs. Right?

If that is deemed valuable, then I think it should be fixed in a
central location, and not individually for each and every driver.

Anyway, not my call, just stating my opinion, but those are the
reasons for me not adding a processed channel from the very beginning.

Cheers,
Peter

> Best regards,
> Mylène
> 
> Mylène Josserand (3):
>   iio: afe: rescale: Move scale conversion to new function
>   iio: afe: rescale: Add support of CHAN_INFO_PROCESSED
>   dt-bindings: iio: afe: Add hwmon example
> 
>  .../bindings/iio/afe/voltage-divider.txt           | 24 ++++++
>  drivers/iio/afe/iio-rescale.c                      | 96 ++++++++++++++++------
>  2 files changed, 96 insertions(+), 24 deletions(-)
>