libcamera: v4l2_device: Add enumeration of pixelformats and frame sizes

Add methods to enumerate pixelformats and frame sizes from a V4L2
device. The interface is similar to how V4L2Subdevice enumerates mbus
codes and frame sizes.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/include/v4l2_device.h

@@ -16,6 +16,7 @@
 #include <libcamera/geometry.h>
 #include <libcamera/signal.h>
 
+#include "formats.h"
 #include "log.h"
 
 namespace libcamera {
@@ -132,6 +133,7 @@ public:
 
 	int getFormat(V4L2DeviceFormat *format);
 	int setFormat(V4L2DeviceFormat *format);
+	ImageFormats formats();
 
 	int exportBuffers(BufferPool *pool);
 	int importBuffers(BufferPool *pool);
@@ -163,6 +165,9 @@ private:
 	int createPlane(Buffer *buffer, unsigned int plane,
 			unsigned int length);
 
+	std::vector<unsigned int> enumPixelformats();
+	std::vector<SizeRange> enumSizes(unsigned int pixelFormat);
+
 	Buffer *dequeueBuffer();
 	void bufferAvailable(EventNotifier *notifier);
 

src/libcamera/v4l2_device.cpp

@@ -634,6 +634,33 @@ int V4L2Device::setFormatSingleplane(V4L2DeviceFormat *format)
 	return 0;
 }
 
+/**
+ * \brief Enumerate all pixel formats and frame sizes
+ *
+ * Enumerate all pixel formats and frame sizes supported by the video device.
+ *
+ * \return A list of the supported device formats
+ */
+ImageFormats V4L2Device::formats()
+{
+	ImageFormats formats;
+
+	for (unsigned int pixelformat : enumPixelformats()) {
+		std::vector<SizeRange> sizes = enumSizes(pixelformat);
+		if (sizes.empty())
+			return {};
+
+		if (formats.addFormat(pixelformat, sizes)) {
+			LOG(V4L2, Error)
+				<< "Could not add sizes for pixel format "
+				<< pixelformat;
+			return {};
+		}
+	}
+
+	return formats;
+}
+
 int V4L2Device::requestBuffers(unsigned int count)
 {
 	struct v4l2_requestbuffers rb = {};
@@ -763,6 +790,93 @@ int V4L2Device::createPlane(Buffer *buffer, unsigned int planeIndex,
 	return 0;
 }
 
+std::vector<unsigned int> V4L2Device::enumPixelformats()
+{
+	std::vector<unsigned int> formats;
+	int ret;
+
+	for (unsigned int index = 0; ; index++) {
+		struct v4l2_fmtdesc pixelformatEnum = {};
+		pixelformatEnum.index = index;
+		pixelformatEnum.type = bufferType_;
+
+		ret = ioctl(fd_, VIDIOC_ENUM_FMT, &pixelformatEnum);
+		if (ret)
+			break;
+
+		formats.push_back(pixelformatEnum.pixelformat);
+	}
+
+	if (ret && errno != EINVAL) {
+		ret = -errno;
+		LOG(V4L2, Error)
+			<< "Unable to enumerate pixel formats: "
+			<< strerror(-ret);
+		return {};
+	}
+
+	return formats;
+}
+
+std::vector<SizeRange> V4L2Device::enumSizes(unsigned int pixelFormat)
+{
+	std::vector<SizeRange> sizes;
+	int ret;
+
+	for (unsigned int index = 0;; index++) {
+		struct v4l2_frmsizeenum frameSize = {};
+		frameSize.index = index;
+		frameSize.pixel_format = pixelFormat;
+
+		ret = ioctl(fd_, VIDIOC_ENUM_FRAMESIZES, &frameSize);
+		if (ret)
+			break;
+
+		if (index != 0 &&
+		    frameSize.type != V4L2_FRMSIZE_TYPE_DISCRETE) {
+			LOG(V4L2, Error)
+				<< "Non-zero index for non discrete type";
+			return {};
+		}
+
+		switch (frameSize.type) {
+		case V4L2_FRMSIZE_TYPE_DISCRETE:
+			sizes.emplace_back(frameSize.discrete.width,
+					   frameSize.discrete.height);
+			break;
+		case V4L2_FRMSIZE_TYPE_CONTINUOUS:
+			sizes.emplace_back(frameSize.stepwise.min_width,
+					   frameSize.stepwise.min_height,
+					   frameSize.stepwise.max_width,
+					   frameSize.stepwise.max_height);
+			break;
+		case V4L2_FRMSIZE_TYPE_STEPWISE:
+			sizes.emplace_back(frameSize.stepwise.min_width,
+					   frameSize.stepwise.min_height,
+					   frameSize.stepwise.max_width,
+					   frameSize.stepwise.max_height,
+					   frameSize.stepwise.step_width,
+					   frameSize.stepwise.step_height);
+			break;
+		default:
+			LOG(V4L2, Error)
+				<< "Unknown VIDIOC_ENUM_FRAMESIZES type "
+				<< frameSize.type;
+			return {};
+		}
+	}
+
+	if (ret && errno != EINVAL) {
+		ret = -errno;
+		LOG(V4L2, Error)
+			<< "Unable to enumerate frame sizes: "
+			<< strerror(-ret);
+		return {};
+	}
+
+	return sizes;
+}
+
 /**
  * \brief Import the externally allocated \a pool of buffers
  * \param[in] pool BufferPool of buffers to import