From: Bruce Mitchell <bruce.mitchell@linux.vnet.ibm.com>
To: Lars-Peter Clausen <lars@metafoo.de>, linux-iio@vger.kernel.org
Cc: "openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>,
Ed Tanous <ed@tanous.net>, Ed Tanous <edtanous@google.com>
Subject: Re: Looking for clarification on sysfs IIO devices, do _raw devices require both _offset and _scale?
Date: Thu, 9 Sep 2021 06:49:19 -0700 [thread overview]
Message-ID: <b9f78f37-fbb6-ea68-48c1-917cf42ca57f@linux.vnet.ibm.com> (raw)
In-Reply-To: <5c79425f-6e88-36b6-cdfe-4080738d039f@metafoo.de>
On 9/9/2021 00:12, Lars-Peter Clausen wrote:
> On 9/9/21 12:10 AM, Bruce Mitchell wrote:
>> In reference to:
>> https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-bus-iio
>>
>> I have Temperature, Pressure, and Humidity IIO sensors.
>> IIO _raw devices look like this on sysfs:
>> this happens to be a SI7020 type device with 2 sensors
>> /sys/bus/iio/devices/iio:device0/in_humidityrelative_offset
>> /sys/bus/iio/devices/iio:device0/in_humidityrelative_raw
>> /sys/bus/iio/devices/iio:device0/in_humidityrelative_scale
>> /sys/bus/iio/devices/iio:device0/in_temp_offset
>> /sys/bus/iio/devices/iio:device0/in_temp_raw
>> /sys/bus/iio/devices/iio:device0/in_temp_scale
>>
>> Other IIO _input devices look like this on sysfs:
>> this happens to be a DPS310 device with 2 sensors
>> /sys/bus/iio/devices/iio:device1/in_temp_input
>> /sys/bus/iio/devices/iio:device1/in_pressure_input
>>
>> As I read it if the IIO device was an _input type on sysfs,
>> just read it (and possibly scale it for units).
>>
>> But if the IIO device was a _raw type on sysfs my understanding
>> is that it must be accompanied by a _offset and a _scale for
>> at least temperature, pressure, humidity, voltage, and current
>> sensors.
>> Is that correct?
>>
>> Further for any IIO device that is a _raw type on sysfs is it
>> required to be accompanied by a _offset and a _scale as well?
>
> Hi,
>
> That sounds about right.
>
> The _input name is historically and comes from hwmon framework. It means
> that the data has been processed by the kernel driver and converted to
> the right SI units for the channel type. This is usually used for sensor
> that have a non-linear transfer function. `raw` on the other hand means
> the data is just as it is reported by the hardware. The reason for this
> is that conversion to SI units is often not lossless, since we have
> finite precision. So it is up to the application to decide whether it
> wants to work on the raw data or how it wants to round the converted data.
>
> `input` attributes never have scale and offset since they are already in
> the right unit. For raw scale and offset are optional. If scale does not
> exist assume it is 1, if offset does not exist assume it is 0. You'll
> rarely see a device with raw attributes without scale, but there are
> quite a few without offset.
>
> - Lars
>
>
Thank you Lars!
--
Bruce
prev parent reply other threads:[~2021-09-09 13:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-08 22:10 Looking for clarification on sysfs IIO devices, do _raw devices require both _offset and _scale? Bruce Mitchell
2021-09-09 7:12 ` Lars-Peter Clausen
2021-09-09 13:49 ` Bruce Mitchell [this message]
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