pipeline: raspberrypi: Read config parameters from a file

Add the ability to read the platform configuration parameters from a
config file provided by the user through the LIBCAMERA_RPI_CONFIG_FILE
environment variable. Use the PipelineHandler::configurationFile()
helper to determine the full path of the file.

Provide an example configuration file named example.yaml. Currently two
parameters are available through the json file:

"min_unicam_buffers" The minimum number of internal Unicam buffers to
allocate.

"min_total_unicam_buffers" The minimum number of internal + external
Unicam buffers that must be allocated.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/src/libcamera/pipeline/raspberrypi/data/example.yaml b/src/libcamera/pipeline/raspberrypi/data/example.yaml
new file mode 100644
index 00000000..4662136e
--- /dev/null
+++ b/src/libcamera/pipeline/raspberrypi/data/example.yaml
@@ -0,0 +1,32 @@
+{
+        "version": 1.0,
+        "target": "bcm2835",
+
+        "pipeline_handler":
+        {
+                # The minimum number of internal buffers to be allocated for
+                # Unicam. This value must be greater than 0, but less than or
+                # equal to min_total_unicam_buffers.
+                #
+                # A larger number of internal buffers can reduce the occurrence
+                # of frame drops during high CPU loads, but might also cause
+                # additional latency in the system.
+                #
+                # Note that the pipeline handler might override this value and
+                # not allocate any internal buffers if it knows they will never
+                # be used. For example if the RAW stream is marked as mandatory
+                # and there are no dropped frames signalled for algorithm
+                # convergence.
+                #
+                # "min_unicam_buffers": 2,
+
+                # The minimum total (internal + external) buffer count used for
+                # Unicam. The number of internal buffers allocated for Unicam is
+                # given by:
+                #
+                # internal buffer count = max(min_unicam_buffers,
+                #         min_total_unicam_buffers - external buffer count)
+                #
+                # "min_total_unicam_buffers": 4
+        }
+}