[libcamera-devel] [PATCH 02/11] ipa: ipu3: Improve the documentation of BDS grid

[Jean-Michel Hautbois]

The BDS grid has its own limitations for the log2 width and height for
each cell of pixels. Use constexpr for those and comment it to help
understanding their usage.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
---
 src/ipa/ipu3/ipu3.cpp | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/ipa/ipu3/ipu3.cpp b/src/ipa/ipu3/ipu3.cpp
index 90053069..c71f2a6c 100644
--- a/src/ipa/ipu3/ipu3.cpp
+++ b/src/ipa/ipu3/ipu3.cpp
@@ -345,6 +345,8 @@ int IPAIPU3::start()
 }
 
 /**
+ * \brief Calculate a grid for the AWB statistics
+ *
  * This function calculates a grid for the AWB algorithm in the IPU3 firmware.
  * Its input is the BDS output size calculated in the ImgU.
  * It is limited for now to the simplest method: find the lesser error
@@ -364,16 +366,24 @@ void IPAIPU3::calculateBdsGrid(const Size &bdsOutputSize)
 	/* Set the BDS output size in the IPAConfiguration structure */
 	context_.configuration.grid.bdsOutputSize = bdsOutputSize;
 
-	for (uint32_t widthShift = 3; widthShift <= 7; ++widthShift) {
+	/*
+	 * The log2 of the width and height of each cell is limited by the ImgU
+	 * in the interval [3, 7] according to the kernel header.
+	 */
+	constexpr uint32_t kCellMin = 3;
+	constexpr uint32_t kCellMax = 7;
+
+	for (uint32_t widthShift = kCellMin; widthShift <= kCellMax; ++widthShift) {
 		uint32_t width = std::min(kMaxCellWidthPerSet,
 					  bdsOutputSize.width >> widthShift);
 		width = width << widthShift;
-		for (uint32_t heightShift = 3; heightShift <= 7; ++heightShift) {
+
+		for (uint32_t heightShift = kCellMin; heightShift <= kCellMax; ++heightShift) {
 			int32_t height = std::min(kMaxCellHeightPerSet,
 						  bdsOutputSize.height >> heightShift);
 			height = height << heightShift;
 			uint32_t error  = std::abs(static_cast<int>(width - bdsOutputSize.width))
-							+ std::abs(static_cast<int>(height - bdsOutputSize.height));
+					+ std::abs(static_cast<int>(height - bdsOutputSize.height));
 
 			if (error > minError)
 				continue;
-- 
2.30.2