libcamera: v4l2_videodevice: Match formats supported by the device

Now that V4L2PixelFormat::fromPixelFormat() returns a list of formats
to chose from, select the one supported by the video device by matching
against the list of supported pixel formats.

The first format found to match one of the device supported ones is
returned.

As the list of pixel formats supported by the video device does not
change at run-time, cache it at device open() time. Maximize the
lookup efficiency by storing the list of supported V4L2PixelFormat in an
std::unordered_set<>.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Paul Elder <paul.elder@ideasonboard.com>

2 files changed, 49 insertions, 12 deletions

diff --git a/include/libcamera/internal/v4l2_videodevice.h b/include/libcamera/internal/v4l2_videodevice.h
index 29fa0bba..ed98a284 100644
--- a/include/libcamera/internal/v4l2_videodevice.h
+++ b/include/libcamera/internal/v4l2_videodevice.h
@@ -14,6 +14,7 @@
 #include <ostream>
 #include <stdint.h>
 #include <string>
+#include <unordered_set>
 #include <vector>
 
 #include <linux/videodev2.h>
@@ -242,6 +243,8 @@ private:
 		Stopped,
 	};
 
+	int initFormats();
+
 	int getFormatMeta(V4L2DeviceFormat *format);
 	int trySetFormatMeta(V4L2DeviceFormat *format, bool set);
 
@@ -268,6 +271,7 @@ private:
 	V4L2Capability caps_;
 	V4L2DeviceFormat format_;
 	const PixelFormatInfo *formatInfo_;
+	std::unordered_set<V4L2PixelFormat> pixelFormats_;
 
 	enum v4l2_buf_type bufferType_;
 	enum v4l2_memory memoryType_;
diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index 2ca22f48..b80ee1cd 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -633,13 +633,9 @@ int V4L2VideoDevice::open()
 		<< "Opened device " << caps_.bus_info() << ": "
 		<< caps_.driver() << ": " << caps_.card();
 
-	ret = getFormat(&format_);
-	if (ret) {
-		LOG(V4L2, Error) << "Failed to get format";
+	ret = initFormats();
+	if (ret)
 		return ret;
-	}
-
-	formatInfo_ = &PixelFormatInfo::info(format_.fourcc);
 
 	return 0;
 }
@@ -726,7 +722,24 @@ int V4L2VideoDevice::open(SharedFD handle, enum v4l2_buf_type type)
 		<< "Opened device " << caps_.bus_info() << ": "
 		<< caps_.driver() << ": " << caps_.card();
 
-	ret = getFormat(&format_);
+	ret = initFormats();
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+int V4L2VideoDevice::initFormats()
+{
+	const std::vector<V4L2PixelFormat> &deviceFormats = enumPixelformats(0);
+	if (deviceFormats.empty()) {
+		LOG(V4L2, Error) << "Failed to initialize device formats";
+		return -EINVAL;
+	}
+
+	pixelFormats_ = { deviceFormats.begin(), deviceFormats.end() };
+
+	int ret = getFormat(&format_);
 	if (ret) {
 		LOG(V4L2, Error) << "Failed to get format";
 		return ret;
@@ -1990,17 +2003,37 @@ V4L2VideoDevice::fromEntityName(const MediaDevice *media,
 }
 
 /**
- * \brief Convert \a PixelFormat to its corresponding V4L2 FourCC
+ * \brief Convert \a PixelFormat to a V4L2PixelFormat supported by the device
  * \param[in] pixelFormat The PixelFormat to convert
  *
- * The V4L2 format variant the function returns the contiguous version
- * unconditionally.
+ * Convert \a pixelformat to a V4L2 FourCC that is known to be supported by
+ * the video device.
  *
- * \return The V4L2_PIX_FMT_* pixel format code corresponding to \a pixelFormat
+ * A V4L2VideoDevice may support different V4L2 pixel formats that map the same
+ * PixelFormat. This is the case of the contiguous and non-contiguous variants
+ * of multiplanar formats, and with the V4L2 MJPEG and JPEG pixel formats.
+ * Converting a PixelFormat to a V4L2PixelFormat may thus have multiple answers.
+ *
+ * This function converts the \a pixelFormat using the list of V4L2 pixel
+ * formats that the V4L2VideoDevice supports. This guarantees that the returned
+ * V4L2PixelFormat will be valid for the device. If multiple matches are still
+ * possible, contiguous variants are preferred. If the \a pixelFormat is not
+ * supported by the device, the function returns an invalid V4L2PixelFormat.
+ *
+ * \return The V4L2PixelFormat corresponding to \a pixelFormat if supported by
+ * the device, or an invalid V4L2PixelFormat otherwise
  */
 V4L2PixelFormat V4L2VideoDevice::toV4L2PixelFormat(const PixelFormat &pixelFormat) const
 {
-	return V4L2PixelFormat::fromPixelFormat(pixelFormat)[0];
+	const std::vector<V4L2PixelFormat> &v4l2PixelFormats =
+		V4L2PixelFormat::fromPixelFormat(pixelFormat);
+
+	for (const V4L2PixelFormat &v4l2Format : v4l2PixelFormats) {
+		if (pixelFormats_.count(v4l2Format))
+			return v4l2Format;
+	}
+
+	return {};
 }
 
 /**