drivers: video: introduce an API for collecting statistics

Introduce an abstraction layer handling the diversity of ways hardware
have to report statistics. This allows to take advantage of the various
channel average or histograms present on some hardware, that skip the
need to manually compute statistics.
Fixes #85457

Signed-off-by: Josuah Demangeon <me@josuah.net>

Author: josuah

include/zephyr/drivers/video.h

@@ -24,7 +24,6 @@
 #include <zephyr/device.h>
 #include <stddef.h>
 #include <zephyr/kernel.h>
-
 #include <zephyr/types.h>
 
 #ifdef __cplusplus
@@ -202,6 +201,75 @@ struct video_frmival_enum {
 	};
 };
 
+/** Custom statistics allowing applications to implement their own format. */
+#define VIDEO_STATS_CUSTOM BIT(0)
+
+/** Channel statistics for the Y (luma) channel. */
+#define VIDEO_STATS_CHANNELS_Y BIT(1)
+
+/** Channel statistics for the R, G, B channels. */
+#define VIDEO_STATS_CHANNELS_RGB BIT(2)
+
+/** Bitmap to ask for any statistics compatible with a @struct video_stats_channels */
+#define VIDEO_STATS_CHANNELS (VIDEO_STATS_CHANNELS_RGB | VIDEO_STATS_CHANNELS_Y)
+
+/** Statistics in the form of an histogram with the Y (luma) channel present. */
+#define VIDEO_STATS_HISTOGRAM_Y BIT(3)
+
+/** Statistics in the form of an histogram with the R, G, B channels present. */
+#define VIDEO_STATS_HISTOGRAM_RGB BIT(4)
+
+/** Bitmap to ask for any statistics compatible with a @struct video_stats_histogram */
+#define VIDEO_STATS_HISTOGRAM (VIDEO_STATS_HISTOGRAM_RGB | VIDEO_STATS_HISTOGRAM_Y)
+
+/**
+ * @brief Statistics base type, present as the first field of the other types.
+ *
+ * This type is to be casted to one of the other "video_..._stats" types. This permits to define
+ * new custom types in application and still use the upstream video API.
+ */
+struct video_stats {
+	/** Bitmak that describes the type of the stats filled */
+	uint16_t flags;
+	/** Frame counter to know if a frame elapsed since the last call. Quickly overflowing. */
+	uint16_t frame_counter;
+};
+
+/**
+ * @brief Per-channel average values.
+ *
+ * Each field represent 8-bit integer values that corresponds to the average value of a channel.
+ */
+struct video_stats_channels {
+	/** Base structure with fields common to all types of statistics. */
+	struct video_stats base;
+	/** The luma channel average. */
+	uint8_t y;
+	/** RGB24-formatted averages. */
+	uint8_t rgb[3];
+};
+
+/**
+ * @brief Statistics about the video image color content.
+ *
+ * Used by software algorithms to control the color balance such as White Balance (AWB),
+ * Black Level Correction (BLC), or control sensors such as Exposure/Gain Control (AEC/AGC).
+ */
+struct video_stats_histogram {
+	/** Base structure with fields common to all types of statistics. */
+	struct video_stats base;
+	/** Storage for the histogram buckets for Y, R, G, B channels in this order.
+	 * The presence of a channel is determined by the bits of @c base.flags.
+	 */
+	uint16_t *data;
+	/** Total number of buckets effectively used, to be divided by the number of channels to
+	 * get the per-channel size.
+	 */
+	size_t size;
+	/** Total number of values added to the historam. */
+	uint32_t nval;
+};
+
 /**
  * @brief video_endpoint_id enum
  *
@@ -348,6 +416,19 @@ typedef int (*video_api_get_caps_t)(const struct device *dev, enum video_endpoin
 typedef int (*video_api_set_signal_t)(const struct device *dev, enum video_endpoint_id ep,
 				      struct k_poll_signal *signal);
 
+/**
+ * @typedef video_api_get_stats_t
+ * @brief Register/Unregister poll signal for buffer events.
+ *
+ * See video_set_signal() for argument descriptions.
+ * @param dev Pointer to the device structure.
+ * @param ep Endpoint ID.
+ * @param stats Pointer to the statistics structure, which must have enough storage for the
+		type of stats requested by the @p stats flags.
+ */
+typedef int (*video_api_get_stats_t)(const struct device *dev, enum video_endpoint_id ep,
+				     struct video_stats *stats);
+
 __subsystem struct video_driver_api {
 	/* mandatory callbacks */
 	video_api_set_format_t set_format;
@@ -364,6 +445,7 @@ __subsystem struct video_driver_api {
 	video_api_set_frmival_t set_frmival;
 	video_api_get_frmival_t get_frmival;
 	video_api_enum_frmival_t enum_frmival;
+	video_api_get_stats_t get_stats;
 };
 
 /**
@@ -500,6 +582,39 @@ static inline int video_enum_frmival(const struct device *dev, enum video_endpoi
 	return api->enum_frmival(dev, ep, fie);
 }
 
+/**
+ * @brief Get image statistics out of the video devices.
+ *
+ * This permits to implement algorithms reacting to statistics about the images
+ * collected by the hadware. For instance, in order to implement an image signal
+ * processor with auto-controls (AEC, AGC, AWB...).
+ *
+ * The driver will read the @p stats flags fields to learn about what the caller wants for
+ * statistics, and update them with the statistics effectively added.
+ *
+ * All memory buffers of @p stats are to be provided by the caller, and the driver will update
+ * the @c size field with the size effectively filled with statistics data.
+ *
+ * @param dev Pointer to the device structure that collects the statistics.
+ * @param ep Endpoint ID from which collect the statistics.
+ * @param stats Pointer to a video statistic structure filled by this device.
+ *
+ * @retval 0 If successful.
+ * @retval -ENOSYS If API is not implemented.
+ * @return other error number otherwise.
+ */
+static inline int video_get_stats(const struct device *dev, enum video_endpoint_id ep,
+				  struct video_stats *stats)
+{
+	const struct video_driver_api *api = (const struct video_driver_api *)dev->api;
+
+	if (api->get_stats == NULL) {
+		return -ENOSYS;
+	}
+
+	return api->get_stats(dev, ep, stats);
+}
+
 /**
  * @brief Enqueue a video buffer.
  *