[RFC PATCH 0/4] rkisp1: Allow usage of more than 4 buffers

[Stefan Klug]

Hi all,

In the rkisp1 pipeline the value of StreamConfiuration.bufferCount is
reset to 4 on validate(). This effectively limits the number of buffers
that are in the loop to 4. As soon as the consumers
(gstream/pipewire...) of the buffers need more than 1 buffer at a time,
we start to see frame drops. Sven resurrected an old series [1] that
solves the issue at the expense of an additional control and breaking
changes in the API.

In the IoB code camp two weeks ago there were some discussions regarding
improvements in the rkisp1 regulation and per-frame-control (PFC). PFC
has been an ongoing topic for quite some time now and it seems to slowly
converge. Still we were hesitant in breaking the API or introducing new
controls before the overall concepts have stabilized enough.

To mitigate the pain mentioned above we came up with a minimal changeset
that allows to request more than 4 buffers. Only 4 (or the pipeline
depth reported by the pipeline) buffers are queued into the device.
This has the same benefits as [1] but doesn't require an API break.

I'm not available this week so I post the patches as RFC only for others
to try out as these were not thoroughly tested. Any feedback is greatly
appreciated.

Best regards,
Stefan


[1] https://patchwork.libcamera.org/project/libcamera/list/?series=5148

Stefan Klug (4):
  libcamera: pipeline_handler: Move waitingRequests_ into camera class
  libcamera: internal: Allow to limit the number of queued requests
  pipeline: rkisp1: Limit the maximum number of buffers queued in
  pipeline: rkisp1: Prperly handle the bufferCount set in the stream
    configuration

 include/libcamera/internal/camera.h           |  2 +
 include/libcamera/internal/pipeline_handler.h |  8 ++--
 src/libcamera/pipeline/rkisp1/rkisp1.cpp      | 12 +++++-
 src/libcamera/pipeline/rkisp1/rkisp1_path.cpp |  6 +--
 src/libcamera/pipeline/rkisp1/rkisp1_path.h   |  4 +-
 src/libcamera/pipeline_handler.cpp            | 37 +++++++++++++------
 6 files changed, 46 insertions(+), 23 deletions(-)

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2.43.0