linux-kernel - Re: [PATCH v3 3/3] iio: distance: srf08: add driver ABI documentation

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Date:   Sun, 22 Jan 2017 22:11:36 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andreas Klinger <ak@...klinger.de>
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        ktsai@...ellamicro.com, wsa@...-dreams.de, robh+dt@...nel.org,
        pawel.moll@....com, mark.rutland@....com,
        ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
        trivial@...nel.org, mranostay@...il.com, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 3/3] iio: distance: srf08: add driver ABI documentation

On 22/01/17 20:41, Andreas Klinger wrote:
> Hi Jonathan,
> 
> see question below.
> 
> Andreas
> 
> 
> Jonathan Cameron <jic23@...nel.org> schrieb am Sun, 22. Jan 13:41:
>> On 17/01/17 13:50, Andreas Klinger wrote:
>>> Add sysfs-bus-iio-distance-srf08 for individual attributes of the driver,
>>> especially:
>>>  - sensitivity which the device documentation calls gain for amplifying the
>>>    signal
>>>  - max_range for limiting the maximum distance for expected echos and
>>>    therefore limiting the time waiting for telegrams
>>>
>>> Signed-off-by: Andreas Klinger <ak@...klinger.de>
>>> ---
>>>  .../ABI/testing/sysfs-bus-iio-distance-srf08       | 27 ++++++++++++++++++++++
>>>  1 file changed, 27 insertions(+)
>>>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-distance-srf08
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-distance-srf08 b/Documentation/ABI/testing/sysfs-bus-iio-distance-srf08
>>> new file mode 100644
>>> index 000000000000..e96c28064748
>>> --- /dev/null
>>> +++ b/Documentation/ABI/testing/sysfs-bus-iio-distance-srf08
>>> @@ -0,0 +1,27 @@
>>> +What		/sys/bus/iio/devices/iio:deviceX/in_distance_raw
>>> +Date:		January 2017
>>> +KernelVersion:	4.11
>>> +Contact:	linux-iio@...r.kernel.org
>>> +Description:
>>> +		Get the current distance in meters between the sensor and
>>> +		the first object recognized
>> Generally no need to document what are effectively standard elements.
>> Just leads to the possibility of disagreements in the docs! 
>> Still no harm here really.
>>> +
>>> +What		/sys/bus/iio/devices/iio:deviceX/sensor_sensitivity
>>> +Date:		January 2017
>>> +KernelVersion:	4.11
>>> +Contact:	linux-iio@...r.kernel.org
>>> +Description:
>>> +		Show or set the gain boost of the amp, from 0-31 range.
>>> +		default 31
>>> +
>>> +What		/sys/bus/iio/devices/iio:deviceX/sensor_max_range
>>> +Date:		January 2017
>>> +KernelVersion:	4.11
>>> +Contact:	linux-iio@...r.kernel.org
>>> +Description:
>>> +		Show or set the maximum range between the sensor and the
>>> +		first object echoed in millimeters.
>>> +		This setting limits the time the driver is waiting for a
>>> +		echo.
>>> +		Can be set between 43 and 11008 in a grid of 43 mm.
>>> +		default 6020
>> This needs to be in the same units as the range - so m.
> 
> Just to clarify:
> There should be a floating point number be passed to the driver and being parsed
> there, e. g.:
> 0.043 or 6.020
> right?
That's fine.  Just use the core functions that are already in place for this in
your own parsing. iio_str_to_fixpoint should do the job for you.

It may seem fiddly but however carefully we pick a base unit we never allow enough
range to represent everything that turns up in the future.  Hence the trickery with
'fixed point' values where we can redefine the two parts.
> 
> Or should this number be passed using the scale attribute like the raw value
> does? So that the scale is used by both the value itself and the attribute.
Interesting point. I'm trying to think of an equivalent where the unit is shared like
this.  The event attributes (thresholds) do use scale, but they aren't really
the same thing...

I think if we wanted to do that we'd need to call it something that made it clear.
More than possible that we'll get a colour sensor down the line with a max range or
something silly like that (focusing optics perhaps?) - so may not always be obvious.

Could stick a _raw on the end of it.

Anyone else reading this and have any thoughts?

Jonathan

> 
>> I'm not 100% sure this is the best ABI we can do for this. However, supporting
>> this as a legacy abi if we come up with something more general will be a very
>> small burden, so lets not stall the driver on this!
>>
>> Jonathan
>>>
>>
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