libcamera: v4l2-format: Add V4L2DeviceFormat

Add a V4L2DeviceFormat class aimed to be used to provide format configuration
requests to a V4L2Device.

Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/include/v4l2_device.h

@@ -53,6 +53,20 @@ struct V4L2Capability final : v4l2_capability {
 	}
 };
 
+class V4L2DeviceFormat
+{
+public:
+	uint32_t width;
+	uint32_t height;
+	uint32_t fourcc;
+
+	struct {
+		uint32_t size;
+		uint32_t bpl;
+	} planesFmt[3];
+	unsigned int planes;
+};
+
 class MediaEntity;
 class V4L2Device
 {

src/libcamera/v4l2_device.cpp

@@ -80,6 +80,62 @@ LOG_DEFINE_CATEGORY(V4L2)
  * \return True if the device provides Streaming I/O IOCTLs
  */
 
+/**
+ * \class V4L2DeviceFormat
+ * \brief The V4L2 device image format and sizes
+ *
+ * Describes the image format and image sizes to be programmed on a V4L2
+ * video device. The image format is defined by fourcc code as defined by
+ * the V4L2 APIs with the V4L2_PIX_FMT_ macros, a visible width and height
+ * and a variable number of planes (1 to 3) with variable sizes and line
+ * strides.
+ *
+ * Formats defined as 'single planar' by the V4L2 APIs are represented with
+ * V4L2DeviceFormat instances with a single plane
+ * (V4L2DeviceFormat::planes = 1). Semi-planar and multiplanar formats use
+ * 2 and 3 planes respectively.
+ *
+ * V4L2DeviceFormat defines the exchange format between components that
+ * receive image configuration requests from applications and a V4L2Device.
+ * The V4L2Device validates and applies the requested size and format to
+ * the device driver.
+ */
+
+/**
+ * \var V4L2DeviceFormat::width
+ * \brief The image width
+ */
+
+/**
+ * \var V4L2DeviceFormat::height
+ * \brief The image height
+ */
+
+/**
+ * \var V4L2DeviceFormat::fourcc
+ * \brief The pixel encoding scheme
+ *
+ * The fourcc code, as defined by the V4L2 APIs with the V4L2_PIX_FMT_ macros,
+ * that identifies the image format pixel encoding scheme.
+ */
+
+/**
+ * \var V4L2DeviceFormat::planesFmt
+ * \brief The per-plane size information
+ *
+ * Images are stored in memory in one or more data planes. Each data plane
+ * has a specific size and line length, which could differ from the image
+ * visible sizes to accommodate line or plane padding data.
+ *
+ * Only the first V4L2DeviceFormat::planes entries are considered valid.
+ *
+ */
+
+/**
+ * \var V4L2DeviceFormat::planes
+ * \brief The number of valid data planes
+ */
+
 /**
  * \class V4L2Device
  * \brief V4L2Device object and API