Re: V4L control units

[Hans Verkuil <hverkuil@xs4all.nl>]

On 05/08/2014 11:04 AM, Sakari Ailus wrote:
> Heippa!
> 
> On Wed, May 07, 2014 at 03:57:11PM +0300, Antti Palosaari wrote:
>> What is preferred way implement controls that could have some known
>> unit or unknown unit? For example for gain controls, I would like to
>> offer gain in unit of dB (decibel) and also some unknown driver
>> specific unit. Should I two controls, one for each unit?
>>
>> Like that
>>
>> V4L2_CID_RF_TUNER_LNA_GAIN_AUTO
>> V4L2_CID_RF_TUNER_LNA_GAIN
>> V4L2_CID_RF_TUNER_LNA_GAIN_dB
> 
> I suppose that on any single device there would be a single unit to control
> a given... control. Some existing controls do document the unit as well but
> I don't think that's scalable nor preferrable. This way we'd have many
> different controls to control the same thing but just using a different
> unit. The auto control is naturally different. Hans did have a patch to add
> the unit to queryctrl (in the form of QUERY_EXT_CTRL).

Well, that's going to be dropped again. There were too many comments about
that during the mini-summit and it was not critical for me.

> 
> <URL:http://www.spinics.net/lists/linux-media/msg73136.html>
> 
> I wish we can get these in relatively soon.

Sakari, I think you will have to push this if you want this done.

One interesting thing to look at: the AVB IEEE 1722.1 standard has extensive
support for all sorts of units. I don't know if you have access to the standard
document, but it might be interesting to look at what they do there.

Regards,

	Hans