Paul Elder
6e62034900
When a MediaDevice is enumerated and populated by the DeviceEnumeratorUdev, there is a possibility that the member device nodes of the media graph would not be ready (either not created, or without proper permissions set by udev yet). The MediaDevice is still passed up to the pipeline handler, where an attempt to access the device nodes will fail in EPERM. This whole issue is especially likely to happen when libcamera is run at system init time. To fix this, we first split DeviceEnumerator::addDevice() into three methods: - createDevice() to simply create the MediaDevice - populateMediaDevice() to populate the MediaDevice - addDevice() to pass the MediaDevice up to the pipeline handler DeviceEnumeratorSysfs calls these methods in succession, similar to what it did before when they were all together as addDevice(). DeviceEnumeratorUdev additionally keeps a map of MediaDevices to a list of pending device nodes (plus some other auxillary maps), and a simple list of orphan device nodes. If a v4l device node is ready and there does not exist any MediaDevice node for it, then it goes to the orphan list, otherwise it is initialized and removed from the pending list of the corresponding MediaDevice in the dependency map. When a MediaDevice is populated via DeviceEnumeratorUdev::populateMediaDevice(), it first checks the orphan list to see if the device nodes it needs are there, otherwise it tries to initialize the device nodes and if it fails, then it adds the device nodes it wants to its list in the dependency map. This allows MediaDevice instances to be created and initialized properly with udev when v4l device nodes in the media graph may not be ready when the MediaDevice is populated. Signed-off-by: Paul Elder <paul.elder@ideasonboard.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
===========
libcamera
===========
**A complex camera support library for Linux, Android, and ChromeOS**
Cameras are complex devices that need heavy hardware image processing
operations. Control of the processing is based on advanced algorithms that must
run on a programmable processor. This has traditionally been implemented in a
dedicated MCU in the camera, but in embedded devices algorithms have been moved
to the main CPU to save cost. Blurring the boundary between camera devices and
Linux often left the user with no other option than a vendor-specific
closed-source solution.
To address this problem the Linux media community has very recently started
collaboration with the industry to develop a camera stack that will be
open-source-friendly while still protecting vendor core IP. libcamera was born
out of that collaboration and will offer modern camera support to Linux-based
systems, including traditional Linux distributions, ChromeOS and Android.
Getting Started
---------------
To build and install:
::
meson build
cd build
ninja
ninja install
Dependencies
------------
The following Debian/Ubuntu packages are required for building libcamera.
Other distributions may have differing package names:
A C++ toolchain: [required]
Either {g++, clang}
for libcamera: [required]
meson ninja-build
for device hotplug enumeration: [optional]
pkg-config libudev-dev
for qcam: [optional]
qtbase5-dev libqt5core5a libqt5gui5 libqt5widgets5
for documentation: [optional]
python3-sphinx doxygen