Re: [PATCH v3 1/2] v4l: Add camera voice coil lens control class, current control

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Sat, 29 Apr 2017 00:00:05 +0200
Pavel Machek <pavel@ucw.cz> escreveu:

> Hi!
> 
> > Hmm... if the idea is to have a control that doesn't do ringing
> > compensation, then it should be clear at the control's descriptions
> > that:
> > 
> > - V4L2_CID_FOCUS_ABSOLUTE should be used if the VCM has ringing
> >   compensation;
> > - V4L2_CID_VOICE_COIL_CURRENT and V4L2_CID_VOICE_COIL_RING_COMPENSATION
> >   should be used otherwise.
> > 
> > Btw, if the rationale for this patch is to support devices without
> > ring compensation, so, both controls and their descriptions should
> > be added at the same time, together with a patchset that would be
> > using both.
> >   
> > > How about adding such an explanation added to the commit message?  
> > 
> > It is not enough. Documentation should be clear that VCM devices
> > with ring compensation should use V4L2_CID_FOCUS_ABSOLUTE.  
> 
> Is ring compensation actually a big deal? We do not publish enough
> information to userland about how fast the autofocus system is,
> anyway, so it looks like userland can't depend on such details...

Well, I guess a V4L2 event could be used to identify the VCM's
current position and/or notify when the movement finished.

Anyway, the point is:

If V4L2_CID_VOICE_COIL_CURRENT would do the same as:
	V4L2_CID_FOCUS_ABSOLUTE
or:
	max - V4L2_CID_FOCUS_ABSOLUTE

there's no reason to create a new control, as the existing control
was already created to control the VCM current [1].

[1] Ok, we need to better document it, but that's a separate issue

We should create a new control only if it is doing something
different than the "standard" way of controlling a Voice Coil Motor.

On such case, the difference between controlling VCM via
V4L2_CID_VOICE_COIL_CURRENT or via V4L2_CID_FOCUS_ABSOLUTE should be 
clearly stated, as we expect that the other devices with the same need 
will implement the same control set and the same max/min convention
(e. g. max integer value meaning closest focus, min integer value
meaning infinite).

Thanks,
Mauro