[libcamera-devel] [RFC 0/2] Add support for pipeline specific data to Cameras

[Niklas Söderlund]

Hi Jacopo,

Thanks for your work.

On 2019-01-22 19:12:23 +0100, Jacopo Mondi wrote:
> RFC as I'm not sure about the idea of delegating ownership of platform data
> to Cameras, as that requires the pipeline handler to dynamically allocate the
> resources (if they go away at pipeline handler destruction time, is pointless
> to store them in Camera).
> 
> The other way around is the idea of borrowing pipeline handler data to Cameras,
> but as Cameras are shared objects, they might stay around longer that pipeline
> handlers, and thus I felt it is safer to tie the CameraData lifetime to the one
> of the Camera instance they're associated to.

While working with the Camera API and it's interaction with the pipeline 
handler I felt a need for something similar you have here. My initial 
idea to avoid lifetime management issues which you deal with in this 
series was for the PipelineHandler to be able to set a unsigned int as a 
cookie on the Camera at creation time, which it could retrieve with it's 
later interaction with a Camera object.

In the end I went a different way, as it became clear we would need an 
two way association between the Camera and the PipelineHandler anyhow.  
That is the PipelineHandler would need to keep a reference to the 
Camera, so I ended up using the pointer to the Camera object as the 
cookie as this like a numerical cookie avoids all lifetime issues. That 
way whenever a PipelineHandler is handed a Camera object it can use the 
pointer to

1. Validate that the Camera object in question really is its 
   responsibility to handle.

2. Use the pointer as a cookie to look-up any camera specific data in 
   its private data structures.

I think that is quiet neat as it uses infrastructure we need anyhow to 
properly manage the interactions between the two objects.

> 
> Thanks
>    j
> 
> Jacopo Mondi (2):
>   libcamera: camera: Add CameraData
>   libcamera: ipu3: Create CIO2 V4L2 devices
> 
>  include/libcamera/camera.h           | 13 ++++++++
>  src/libcamera/camera.cpp             | 50 ++++++++++++++++++++++++++++
>  src/libcamera/pipeline/ipu3/ipu3.cpp | 42 +++++++++++++++++++++++
>  3 files changed, 105 insertions(+)
> 
> --
> 2.20.1
> 
> _______________________________________________
> libcamera-devel mailing list
> libcamera-devel at lists.libcamera.org
> https://lists.libcamera.org/listinfo/libcamera-devel

-- 
Regards,
Niklas Söderlund