Currently, libcamera can be configured in runtime using several
environment variables. With introducing more and more variables, this
mechanism reaches its limits. It would be simpler and more flexible if
it was possible to configure libcamera in a single file.
For example, there was a request to define pipeline precedence in
runtime. We want to compile in multiple pipelines, in order to have
them accessible within single packages in distributions. And then being
able to select among the pipelines manually as needed based on the
particular hardware or operating system environment. Having the
configuration file then allows easy switching between hardware, GPU or
CPU IPAs. The configuration file can also be used to enable or disable
experimental features and avoid the need to track local patches changing
configuration options hard-wired in the code when working on new
features.
This patch introduces basic support for configuration files.
GlobalConfiguration class reads and stores the configuration. Its
instance can be used by other libcamera objects to access the
configuration. A GlobalConfiguration instance is supposed to be stored
in a well-defined place, e.g. a CameraManager instance. It is possible
to have multiple GlobalConfiguration instances, which may or may not
make sense.
libcamera configuration can be specified using a system-wide
configuration file or a user configuration file. The user configuration
file takes precedence if present. There is currently no way to merge
multiple configuration files, the one found is used as the only
configuration file. If no configuration file is present, nothing
changes to the current libcamera behavior (except for some log
messages related to configuration file lookup).
The configuration file is a YAML file. We already have a mechanism for
handling YAML configuration files in libcamera and the given
infrastructure can be reused for the purpose. However, the
configuration type is abstracted to make contingent future change of the
underlying class easier while retaining (most of) the original API.
The configuration is versioned. This has currently no particular
meaning but is likely to have its purpose in future, especially once
configuration validation is introduced.
The configuration YAML file looks as follows:
---
version: 1
configuration:
WHATEVER CONFIGURATION NEEDED
This patch introduces just the basic idea. Actually using the
configuration in the corresponding places (everything what is currently
configurable via environment variables should be configurable in the
file configuration) and other enhancements are implemented in the
followup patches.
Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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