libcamera: Add link handling functions

Add a function to the MediaLink class to set the state of a link to
enabled or disabled. The function makes use of an internal MediaDevice
method, which is defined private and only accessible by the MediaLink
setEnabled() function itself.

Also add to MediaDevice a function to reset all links registered in the
media graph.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

4 files changed, 109 insertions, 0 deletions

diff --git a/src/libcamera/include/media_device.h b/src/libcamera/include/media_device.h
index 22c32b7e..a8dec0d3 100644
--- a/src/libcamera/include/media_device.h
+++ b/src/libcamera/include/media_device.h
@@ -45,6 +45,7 @@ public:
 	MediaLink *link(const MediaEntity *source, unsigned int sourceIdx,
 			const MediaEntity *sink, unsigned int sinkIdx);
 	MediaLink *link(const MediaPad *source, const MediaPad *sink);
+	int disableLinks();
 
 private:
 	std::string driver_;
@@ -65,6 +66,9 @@ private:
 	bool populateEntities(const struct media_v2_topology &topology);
 	bool populatePads(const struct media_v2_topology &topology);
 	bool populateLinks(const struct media_v2_topology &topology);
+
+	friend int MediaLink::setEnabled(bool enable);
+	int setupLink(const MediaLink *link, unsigned int flags);
 };
 
 } /* namespace libcamera */
diff --git a/src/libcamera/include/media_object.h b/src/libcamera/include/media_object.h
index b2c3d8e9..7fc44415 100644
--- a/src/libcamera/include/media_object.h
+++ b/src/libcamera/include/media_object.h
@@ -41,6 +41,7 @@ public:
 	MediaPad *source() const { return source_; }
 	MediaPad *sink() const { return sink_; }
 	unsigned int flags() const { return flags_; }
+	int setEnabled(bool enable);
 
 private:
 	friend class MediaDevice;
diff --git a/src/libcamera/media_device.cpp b/src/libcamera/media_device.cpp
index ca12caaa..0ee55060 100644
--- a/src/libcamera/media_device.cpp
+++ b/src/libcamera/media_device.cpp
@@ -387,6 +387,35 @@ MediaLink *MediaDevice::link(const MediaPad *source, const MediaPad *sink)
 }
 
 /**
+ * \brief Disable all links in the media device
+ *
+ * Disable all the media device links, clearing the MEDIA_LNK_FL_ENABLED flag
+ * on links which are not flagged as IMMUTABLE.
+ *
+ * \return 0 on success, or a negative error code otherwise
+ */
+int MediaDevice::disableLinks()
+{
+	for (MediaEntity *entity : entities_) {
+		for (MediaPad *pad : entity->pads()) {
+			if (!(pad->flags() & MEDIA_PAD_FL_SOURCE))
+				continue;
+
+			for (MediaLink *link : pad->links()) {
+				if (link->flags() & MEDIA_LNK_FL_IMMUTABLE)
+					continue;
+
+				int ret = link->setEnabled(false);
+				if (ret)
+					return ret;
+			}
+		}
+	}
+
+	return 0;
+}
+
+/**
  * \var MediaDevice::objects_
  * \brief Global map of media objects (entities, pads, links) keyed by their
  * object id.
@@ -602,4 +631,50 @@ bool MediaDevice::populateLinks(const struct media_v2_topology &topology)
 	return true;
 }
 
+/**
+ * \brief Apply \a flags to a link between two pads
+ * \param link The link to apply flags to
+ * \param flags The flags to apply to the link
+ *
+ * This function applies the link \a flags (as defined by the MEDIA_LNK_FL_*
+ * macros from the Media Controller API) to the given \a link. It implements
+ * low-level link setup as it performs no checks on the validity of the \a
+ * flags, and assumes that the supplied \a flags are valid for the link (e.g.
+ * immutable links cannot be disabled).
+*
+ * \sa MediaLink::setEnabled(bool enable)
+ *
+ * \return 0 on success, or a negative error code otherwise
+ */
+int MediaDevice::setupLink(const MediaLink *link, unsigned int flags)
+{
+	struct media_link_desc linkDesc = { };
+	MediaPad *source = link->source();
+	MediaPad *sink = link->sink();
+
+	linkDesc.source.entity = source->entity()->id();
+	linkDesc.source.index = source->index();
+	linkDesc.source.flags = MEDIA_PAD_FL_SOURCE;
+
+	linkDesc.sink.entity = sink->entity()->id();
+	linkDesc.sink.index = sink->index();
+	linkDesc.sink.flags = MEDIA_PAD_FL_SINK;
+
+	linkDesc.flags = flags;
+
+	int ret = ioctl(fd_, MEDIA_IOC_SETUP_LINK, &linkDesc);
+	if (ret) {
+		ret = -errno;
+		LOG(Error) << "Failed to setup link: " << strerror(-ret);
+		return ret;
+	}
+
+	LOG(Debug) << source->entity()->name() << "["
+		   << source->index() << "] -> "
+		   << sink->entity()->name() << "["
+		   << sink->index() << "]: " << flags;
+
+	return 0;
+}
+
 } /* namespace libcamera */
diff --git a/src/libcamera/media_object.cpp b/src/libcamera/media_object.cpp
index 4ff9620d..cb3af85e 100644
--- a/src/libcamera/media_object.cpp
+++ b/src/libcamera/media_object.cpp
@@ -15,6 +15,7 @@
 #include <linux/media.h>
 
 #include "log.h"
+#include "media_device.h"
 #include "media_object.h"
 
 /**
@@ -96,6 +97,34 @@ namespace libcamera {
  */
 
 /**
+ * \brief Enable or disable a link
+ * \param enable True to enable the link, false to disable it
+ *
+ * Set the status of a link according to the value of \a enable.
+ * Links between two pads can be set to the enabled or disabled state freely,
+ * unless they're immutable links, whose status cannot be changed.
+ * Enabling an immutable link is not considered an error, while trying to
+ * disable it is.
+ *
+ * Enabling a link establishes a data connection between two pads, while
+ * disabling it interrupts that connection.
+ *
+ * \return 0 on success, or a negative error code otherwise
+ */
+int MediaLink::setEnabled(bool enable)
+{
+	unsigned int flags = enable ? MEDIA_LNK_FL_ENABLED : 0;
+
+	int ret = dev_->setupLink(this, flags);
+	if (ret)
+		return ret;
+
+	flags_ = flags;
+
+	return 0;
+}
+
+/**
  * \brief Construct a MediaLink
  * \param link The media link kernel data
  * \param source The source pad at the origin of the link