From b2eccef711e621748c90fe5bf69ae91d1bd901e8 Mon Sep 17 00:00:00 2001 From: Stanislaw Gruszka Date: Thu, 3 Apr 2025 09:45:47 +0200 Subject: libcamera: v4l2_device: add frame start event helpers 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 # v3 Reviewed-by: Laurent Pinchart # v5 Signed-off-by: Stanislaw Gruszka Signed-off-by: Kieran Bingham --- include/libcamera/internal/v4l2_device.h | 1 + src/libcamera/v4l2_device.cpp | 22 ++++++++++++++++++++++ 2 files changed, 23 insertions(+) diff --git a/include/libcamera/internal/v4l2_device.h b/include/libcamera/internal/v4l2_device.h index affe52c2..a647c96a 100644 --- a/include/libcamera/internal/v4l2_device.h +++ b/include/libcamera/internal/v4l2_device.h @@ -45,6 +45,7 @@ public: const std::string &deviceNode() const { return deviceNode_; } std::string devicePath() const; + bool supportsFrameStartEvent(); int setFrameStartEnabled(bool enable); Signal frameStart; diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp index 2f65a43a..0db92c19 100644 --- a/src/libcamera/v4l2_device.cpp +++ b/src/libcamera/v4l2_device.cpp @@ -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 -- cgit v1.2.1