[libcamera-devel] Optic handling questions

[Matthias Fend]

Hi all,

I have some questions about handling the optic controls. It looks like 
this has been considered, but apart from the use of a simple focus lens 
in IPU3, it doesn't seem to be used extensively yet.

As I understand it, the current control flow looks something like this:
- IPA sets v4l2 control (e.g. V4L2_CID_FOCUS_ABSOLUTE)
- Control is passed to the pipeline handler
- Pipeline handler reads values from known v4l2 controls (e.g. 
V4L2_CID_FOCUS_ABSOLUTE)
- Pipeline handler calls dedicated CameraLens methods (e.g. 
setFocusPosition)
- CameraLens then actually converts to v4l2 control (e.g. 
V4L2_CID_FOCUS_ABSOLUTE) and applies it to sub device

At first glance, it looks like the controls are being unnecessarily 
converted back and forth once, and I'm wondering if the pipeline handler 
really needs to be included in this way here.
Currently that would mean that every pipeline handler needs to know how 
to convert all v4l2 lens-specific controls (like V4L2_CID_ZOOM_ABSOLUTE, 
V4L2_CID_IRIS_ABSOLUTE, ...) into CameraLens methods.
Since the IPAs are already working with v4l2 controls and need to know 
all the lens details, wouldn't it be easier if those controls were 
passed directly to the subdevice?
The pipeline handler's involvement would then be reduced to finding the 
appropriate subdevice and then transparently passing the v4l2 controls 
from the IPA to the device.

But maybe I'm missing something crucial here.
I would be happy about any hints and I would also be interested to know 
if there are already plans in which direction this topic should develop.

Thanks
  ~Matthias