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libcamera: v4l2_device: add frame start event helpers

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Add helper to check if frame start event are supported by subdevice.
Since kernel does not have interface to query supported events
use subscribe interface.

Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com> # v3
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> # v5
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
Stanislaw Gruszka 2025-04-03 09:45:47 +02:00 • committed by Kieran Bingham
parent a2a7f4fc2d
commit b2eccef711
2 changed files with 23 additions and 0 deletions
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1
include/libcamera/internal/v4l2_device.h
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@ -45,6 +45,7 @@ public:
const std::string &deviceNode() const { return deviceNode_; }
std::string devicePath() const;
bool supportsFrameStartEvent();
int setFrameStartEnabled(bool enable);
Signal<uint32_t> frameStart;

22
src/libcamera/v4l2_device.cpp
View file

@ -449,6 +449,28 @@ std::string V4L2Device::devicePath() const
return path;
}
/**
* \brief Check if frame start event is supported
*
* Due to limitations in the kernel API, this function may disable the frame
* start event as a side effect. It should only be called during initialization,
* before enabling the frame start event with setFrameStartEnabled().
*
* \return True if frame start event is supported, false otherwise
*/
bool V4L2Device::supportsFrameStartEvent()
{
struct v4l2_event_subscription event{};
event.type = V4L2_EVENT_FRAME_SYNC;
int ret = ioctl(VIDIOC_SUBSCRIBE_EVENT, &event);
if (ret)
return false;
ioctl(VIDIOC_UNSUBSCRIBE_EVENT, &event);
return true;
}
/**
* \brief Enable or disable frame start event notification
* \param[in] enable True to enable frame start events, false to disable them