[libcamera-devel] [PATCH 0/2] Support resource acquisition at 'acquire()'

[Laurent Pinchart]

Hi Kieran,

On Wed, Nov 16, 2022 at 12:17:22AM +0000, Kieran Bingham via libcamera-devel wrote:
> Pipeline handlers may benefit from being able to postpone resource
> acquisition until the acquire() operation, or even release any temporary
> resources used during initialisation and only use them when acquired.
> 
> This series hopes to balance the updates to the
> PipelineHandler->release(Camera) call, with a corresponding
> PipelineHandler->acquire(camera) and facilitate pipeline handlers
> managing resources only when the camera is in use.
> 
> While the pipeline patch could make some progress, the uvcvideo patch in
> this series is not working. I fear this may be a symptom of a bug in
> either our thread or fdNotifier / event mechanisms, but haven't been
> able to track it down yet.

Did you read my reply to the patch that introduces releaseDevice() ? One
of my concerns is that it ties resource lifetime to ownership lifetime,
which makes it impossible to keep a device acquired for exclusive access
without also holding onto resources.

Could you please expand on the design rationale for this series ? The
rationale should also be reflected in high-level documentation.

> Kieran Bingham (2):
>   libcamera: pipeline: Add an acquireDevice method
>   [DNI/RFC] pipeline: uvcvideo: Only open devices upon acquire
> 
>  include/libcamera/internal/pipeline_handler.h |  3 +-
>  src/libcamera/camera.cpp                      |  2 +-
>  src/libcamera/pipeline/uvcvideo/uvcvideo.cpp  | 55 +++++++++++++++----
>  src/libcamera/pipeline_handler.cpp            | 23 +++++++-

Missing update to the pipeline handler writer's guide (releaseDevice()
also needs to be documented).

>  4 files changed, 69 insertions(+), 14 deletions(-)

-- 
Regards,

Laurent Pinchart