[1/3] libcamera: pipeline: Allow pipeline-handlers to opt out of locking the media devices
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Message ID 20260408115630.12456-2-johannes.goede@oss.qualcomm.com
State New
Headers show
Series
  • libcamera: Finer grained MediaDevice locking
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Commit Message

Hans de Goede April 8, 2026, 11:56 a.m. UTC 
On Qualcomm chips any CSI-phy can be connected to any CSI-decoder and
any CSI-decoder can be connected to any Video-Front-End (VFE, DMA write
engine and co). Basically there are 2 big cross-switches between PHYs
and decoders and between decoders and VFEs which can be controlled through
media-controller links.

As such the entite CAMSS block with CSI-phys, decoders and VFEs is
represented to userspace as a single /dev/media# node.

As long as active links from unrelated cameras are not touched when setting
up a new camera 2 independent raw data-streams can be run and managed by 2
different libcamera instances.

But the standard locking of the /dev/media# node by the first libcamera
instance to start streaming from one of the camera blocks this.

Add a new lockOnAcquire_ class member which defaults to true and allow
pipeline-handlers to opt out of the /dev/media# locking by setting this
to false.

Note pipeline-handlers which opt-out will need to implement their own
alternative locking from acquireDevice(). This could be done for example
by using lockf() on the phy, decoder and VFE v4l2-subdevs used by
the camera being acquired.

Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
---
 include/libcamera/internal/pipeline_handler.h | 2 ++
 src/libcamera/pipeline_handler.cpp            | 8 ++++----
 2 files changed, 6 insertions(+), 4 deletions(-)

Patch
diff mbox series 

diff --git a/include/libcamera/internal/pipeline_handler.h b/include/libcamera/internal/pipeline_handler.h
index b4f97477a..1c88d2e99 100644
--- a/include/libcamera/internal/pipeline_handler.h
+++ b/include/libcamera/internal/pipeline_handler.h
@@ -70,6 +70,7 @@  public:
 
 	CameraManager *cameraManager() const { return manager_; }
 
+
 protected:
 	void registerCamera(std::shared_ptr<Camera> camera);
 	void hotplugMediaDevice(std::shared_ptr<MediaDevice> media);
@@ -83,6 +84,7 @@  protected:
 
 	CameraManager *manager_;
 	const unsigned int maxQueuedRequestsDevice_;
+	bool lockOnAcquire_;
 
 private:
 	void unlockMediaDevices();
diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
index 5c469e5ba..34bfda4af 100644
--- a/src/libcamera/pipeline_handler.cpp
+++ b/src/libcamera/pipeline_handler.cpp
@@ -72,7 +72,7 @@  LOG_DEFINE_CATEGORY(Pipeline)
 PipelineHandler::PipelineHandler(CameraManager *manager,
 				 unsigned int maxQueuedRequestsDevice)
 	: manager_(manager), maxQueuedRequestsDevice_(maxQueuedRequestsDevice),
-	  useCount_(0)
+	  lockOnAcquire_(true), useCount_(0)
 {
 }
 
@@ -170,7 +170,7 @@  PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,
  */
 bool PipelineHandler::acquire(Camera *camera)
 {
-	if (useCount_ == 0) {
+	if (useCount_ == 0 && lockOnAcquire_) {
 		for (std::shared_ptr<MediaDevice> &media : mediaDevices_) {
 			if (!media->lock()) {
 				unlockMediaDevices();
@@ -180,7 +180,7 @@  bool PipelineHandler::acquire(Camera *camera)
 	}
 
 	if (!acquireDevice(camera)) {
-		if (useCount_ == 0)
+		if (useCount_ == 0 && lockOnAcquire_)
 			unlockMediaDevices();
 
 		return false;
@@ -212,7 +212,7 @@  void PipelineHandler::release(Camera *camera)
 
 	releaseDevice(camera);
 
-	if (useCount_ == 1)
+	if (useCount_ == 1 && lockOnAcquire_)
 		unlockMediaDevices();
 
 	--useCount_;