driver: video: ctrls: add VIDEO_CID_DIGITAL_GAIN

Only VIDEO_CID_ANALOGUE_GAIN and VIDEO_CID_GAIN were defined. Also add
the complementary VIDEO_CID_DIGITAL_GAIN.

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

Author: josuah

drivers/video/video_ctrls.c

@@ -544,6 +544,8 @@ static inline const char *video_get_ctrl_name(uint32_t id)
 		return "Test Pattern";
 	case VIDEO_CID_LINK_FREQ:
 		return "Link Frequency";
+	case VIDEO_CID_DIGITAL_GAIN:
+		return "Digital Gain";
 	default:
 		return NULL;
 	}

include/zephyr/drivers/video-controls.h

@@ -349,7 +349,10 @@ enum video_camera_orientation {
  */
 #define VIDEO_CID_IMAGE_SOURCE_CLASS_BASE 0x009e0900
 
-/** Analogue gain control. */
+/** Analogue gain is gain affecting all colour components in the pixel
+ * matrix. The gain operation is performed in the analogue domain
+ * before A/D conversion.
+ */
 #define VIDEO_CID_ANALOGUE_GAIN (VIDEO_CID_IMAGE_SOURCE_CLASS_BASE + 3)
 
 /**
@@ -371,6 +374,14 @@ enum video_camera_orientation {
 /** Selection of the type of test pattern to represent */
 #define VIDEO_CID_TEST_PATTERN (VIDEO_CID_IMAGE_PROC_CLASS_BASE + 3)
 
+/** Digital gain is the value by which all colour components
+ * are multiplied by. Typically the digital gain applied is the
+ * control value divided by e.g. 0x100, meaning that to get no
+ * digital gain the control value needs to be 0x100. The no-gain
+ * configuration is also typically the default.
+ */
+#define VIDEO_CID_DIGITAL_GAIN (VIDEO_CID_IMAGE_PROC_CLASS_BASE + 5)
+
 /**
  * @}
  */