libcamera: media_device: Get entity by regexp

Some kernel drivers give their entities names that will differ from
implementation to implementation; for example the drivers for the
Camera Receiver Unit and CSI-2 receiver in the RZ/V2H(P) SoC give their
entities names that include their memory address, in the format
"csi-16000400.csi2". Passing that entity name to
MediaDevice::getEntityByName() is too inflexible given it would only
then work if that specific CSI-2 receiver were the one being used.

Add an overload for MediaDevice::getEntityByName() that accepts a
std::basic_regex instead of a string, and use std::regex_search()
instead of a direct string comparison to find a matching entity. This
allows us to search for entites using regex patterns like
"csi-[0-9a-f]{8}.csi2".

Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

include/libcamera/internal/media_device.h

@@ -15,6 +15,7 @@
 #include <linux/media.h>
 
 #include <libcamera/base/log.h>
+#include <libcamera/base/regex.h>
 #include <libcamera/base/signal.h>
 #include <libcamera/base/unique_fd.h>
 
@@ -47,6 +48,7 @@ public:
 
 	const std::vector<MediaEntity *> &entities() const { return entities_; }
 	MediaEntity *getEntityByName(const std::string &name) const;
+	MediaEntity *getEntityByName(const std::regex &name) const;
 
 	MediaLink *link(const std::string &sourceName, unsigned int sourceIdx,
 			const std::string &sinkName, unsigned int sinkIdx);

src/libcamera/media_device.cpp

@@ -342,6 +342,32 @@ MediaEntity *MediaDevice::getEntityByName(const std::string &name) const
 	return nullptr;
 }
 
+/**
+ * \brief Return the MediaEntity with name matching the regex \a name
+ * \param[in] name A regex to match the entity name
+ * \return The entity matching the regex \a name, or nullptr if no such entity
+ * is found or multiple entities match on \a name
+ */
+MediaEntity *MediaDevice::getEntityByName(const std::regex &name) const
+{
+	MediaEntity *entity = nullptr;
+
+	for (MediaEntity *e : entities_) {
+		if (!std::regex_search(e->name(), name))
+			continue;
+
+		if (entity) {
+			LOG(MediaDevice, Error)
+				<< "Multiple entities match given regex";
+			return nullptr;
+		}
+
+		entity = e;
+	}
+
+	return entity;
+}
+
 /**
  * \brief Retrieve the MediaLink connecting two pads, identified by entity
  * names and pad indexes