libcamera: media_device: Move recursive lock handling to pipeline handler

The MediaDevice lock is meant to prevent concurrent usage of multiple
cameras from the same pipeline handlers. As media devices are acquired
by pipeline handlers, we can't have multiple pipeline handlers trying to
lock the same media device. The recursive locking detection can thus be
moved to the pipeline handler. This simplifies the media device
implementation that now implements true lock semantics, and prepares for
support of concurrent camera usage.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

2 files changed, 13 insertions, 14 deletions

diff --git a/src/libcamera/media_device.cpp b/src/libcamera/media_device.cpp
index 0b794018..941f86c2 100644
--- a/src/libcamera/media_device.cpp
+++ b/src/libcamera/media_device.cpp
@@ -63,8 +63,7 @@ LOG_DEFINE_CATEGORY(MediaDevice)
  * populate() before the media graph can be queried.
  */
 MediaDevice::MediaDevice(const std::string &deviceNode)
-	: deviceNode_(deviceNode), valid_(false), acquired_(false),
-	  lockOwner_(false)
+	: deviceNode_(deviceNode), valid_(false), acquired_(false)
 {
 }
 
@@ -145,15 +144,9 @@ bool MediaDevice::lock()
 	if (!fd_.isValid())
 		return false;
 
-	/* Do not allow nested locking in the same libcamera instance. */
-	if (lockOwner_)
-		return false;
-
 	if (lockf(fd_.get(), F_TLOCK, 0))
 		return false;
 
-	lockOwner_ = true;
-
 	return true;
 }
 
@@ -171,11 +164,6 @@ void MediaDevice::unlock()
 	if (!fd_.isValid())
 		return;
 
-	if (!lockOwner_)
-		return;
-
-	lockOwner_ = false;
-
 	lockf(fd_.get(), F_ULOCK, 0);
 }
 
diff --git a/src/libcamera/pipeline_handler.cpp b/src/libcamera/pipeline_handler.cpp
index 0bc0e341..a9241ac6 100644
--- a/src/libcamera/pipeline_handler.cpp
+++ b/src/libcamera/pipeline_handler.cpp
@@ -67,7 +67,7 @@ LOG_DEFINE_CATEGORY(Pipeline)
  * respective factories.
  */
 PipelineHandler::PipelineHandler(CameraManager *manager)
-	: manager_(manager)
+	: manager_(manager), lockOwner_(false)
 {
 }
 
@@ -155,6 +155,10 @@ MediaDevice *PipelineHandler::acquireMediaDevice(DeviceEnumerator *enumerator,
  */
 bool PipelineHandler::lock()
 {
+	/* Do not allow nested locking in the same libcamera instance. */
+	if (lockOwner_)
+		return false;
+
 	for (std::shared_ptr<MediaDevice> &media : mediaDevices_) {
 		if (!media->lock()) {
 			unlock();
@@ -162,6 +166,8 @@ bool PipelineHandler::lock()
 		}
 	}
 
+	lockOwner_ = true;
+
 	return true;
 }
 
@@ -177,8 +183,13 @@ bool PipelineHandler::lock()
  */
 void PipelineHandler::unlock()
 {
+	if (!lockOwner_)
+		return;
+
 	for (std::shared_ptr<MediaDevice> &media : mediaDevices_)
 		media->unlock();
+
+	lockOwner_ = false;
 }
 
 /**