[libcamera-devel] [PATCH 0/1] Generalized DeviceMatch

[Jacopo Mondi]

Hi Sophie,
  sorry for the very long delay in reviewing this patch

let me cc Harvey which, as you might know, is working on adding a
pipeline handler implementation that does not use the media device
abstraction.

Harvey: Sophie is instead introducing a generalized form of device
matching that can be made to use different identifiers than the media
entities names. I wonder if this is something that could help with
virtual pipeline (see below)

On Thu, Mar 02, 2023 at 01:54:14AM +0100, Sophie Friedrich via libcamera-devel wrote:
> In preparation for introducing libusb support into libcamera, we need
> to generalize the matching functionality. The `MediaEntity` class was
> never meant to handle the cases required for e.g. libusb. Additionally
> the current way matching is handled is insufficient for (future)
> `MediaDevices` in which a specific key/value relationship exists
> for properties (e.g. USB vid and pid).

Do I get it right that you plan to use the vid as key and the pid as
value ?

>
> To solve these two problems I've abstracted away the requirements for
> entities that `DeviceMatch` requires in `DeviceMatchEntityInterface`
> and extended `DeviceMatch` to handle key/value pairs. Using "*" as a
> key is currently a catch all for the presumably keyless property of
> V4L2 `MediaEntity`.

Harvey: my understanding is that your plan is to define the number of
virtual cameras in a configuration file. I wonder if by introducing a
device enumerator that parses the configuration file we could create
some form of matching for the Virtual pipeline handler.

The "ConfigurationFileDeviceEnumerator" would define a number of
"virtual instances" and the virtual pipeline handler will be matches
against each of them. This would allow to create multiple instances of
the virtual pipeline handler to test it, and in future, if this would
ever be useful, to match different version of the virtual pipeline
handler against different 'tags' specified in the configuration. Do
you think it's something that might prove useful ?

>
> Sophie Friedrich (1):
>   libcamera: enumeration: Generalize DeviceMatch
>
>  .../libcamera/internal/device_enumerator.h    |  16 +--
>  include/libcamera/internal/device_match.h     |  46 +++++++
>  include/libcamera/internal/media_device.h     |   1 +
>  include/libcamera/internal/media_object.h     |   7 +-
>  include/libcamera/internal/meson.build        |   1 +
>  src/libcamera/device_enumerator.cpp           |  73 ----------
>  src/libcamera/device_match.cpp                | 126 ++++++++++++++++++
>  src/libcamera/meson.build                     |   1 +
>  8 files changed, 183 insertions(+), 88 deletions(-)
>  create mode 100644 include/libcamera/internal/device_match.h
>  create mode 100644 src/libcamera/device_match.cpp
>
> --
> 2.34.1
>