ipa: rkisp1: Introduce AWB

The RkISP1 ISP calculates a mean value for Y, Cr and Cb at each frame.
There is a RGB mode which could theoretically give us the values for R,
G and B directly, but it seems to be failing right now.

Convert those values into R, G and B and estimate the gain to apply in a
grey world.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Tested-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/ipa/rkisp1/ipa_context.cpp

@@ -81,6 +81,14 @@ namespace libcamera::ipa::rkisp1 {
  * \brief Hardware revision of the ISP
  */
 
+/**
+ * \var IPASessionConfiguration::awb
+ * \brief AWB parameters configuration of the IPA
+ *
+ * \var IPASessionConfiguration::awb.measureWindow
+ * \brief AWB measure window
+ */
+
 /**
  * \var IPASessionConfiguration::sensor
  * \brief Sensor-specific configuration of the IPA
@@ -105,6 +113,26 @@ namespace libcamera::ipa::rkisp1 {
  * The gain should be adapted to the sensor specific gain code before applying.
  */
 
+/**
+ * \var IPAFrameContext::awb
+ * \brief Context for the Automatic White Balance algorithm
+ *
+ * \struct IPAFrameContext::awb.gains
+ * \brief White balance gains
+ *
+ * \var IPAFrameContext::awb.gains.red
+ * \brief White balance gain for R channel
+ *
+ * \var IPAFrameContext::awb.gains.green
+ * \brief White balance gain for G channel
+ *
+ * \var IPAFrameContext::awb.gains.blue
+ * \brief White balance gain for B channel
+ *
+ * \var IPAFrameContext::awb.temperatureK
+ * \brief Estimated color temperature
+ */
+
 /**
  * \var IPAFrameContext::sensor
  * \brief Effective sensor values