Make the code more robust and improve readability by using bitfield
macros instead of open coding bit operations.
While at it, also add a definition for LUT_BITS_DEFAULT.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
---
 drivers/gpu/drm/mediatek/mtk_disp_gamma.c | 41 ++++++++++++++---------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_disp_gamma.c b/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
index b9dc8754187d..4f642fed432f 100644
--- a/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
+++ b/drivers/gpu/drm/mediatek/mtk_disp_gamma.c
@@ -3,6 +3,7 @@
  * Copyright (c) 2021 MediaTek Inc.
  */
 
+#include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/component.h>
 #include <linux/module.h>
@@ -21,9 +22,16 @@
 #define GAMMA_LUT_EN					BIT(1)
 #define GAMMA_DITHERING					BIT(2)
 #define DISP_GAMMA_SIZE				0x0030
+#define DISP_GAMMA_SIZE_HSIZE				GENMASK(28, 16)
+#define DISP_GAMMA_SIZE_VSIZE				GENMASK(12, 0)
 #define DISP_GAMMA_LUT				0x0700
 
+#define DISP_GAMMA_LUT_10BIT_R			GENMASK(29, 20)
+#define DISP_GAMMA_LUT_10BIT_G			GENMASK(19, 10)
+#define DISP_GAMMA_LUT_10BIT_B			GENMASK(9, 0)
+
 #define LUT_10BIT_MASK				0x03ff
+#define LUT_BITS_DEFAULT			10
 
 struct mtk_disp_gamma_data {
 	bool has_dither;
@@ -90,33 +98,33 @@ void mtk_gamma_set_common(struct device *dev, void __iomem *regs,
 	for (i = 0; i < lut_size; i++) {
 		struct drm_color_lut diff, hwlut;
 
-		hwlut.red = drm_color_lut_extract(lut[i].red, 10);
-		hwlut.green = drm_color_lut_extract(lut[i].green, 10);
-		hwlut.blue = drm_color_lut_extract(lut[i].blue, 10);
+		hwlut.red = drm_color_lut_extract(lut[i].red, LUT_BITS_DEFAULT);
+		hwlut.green = drm_color_lut_extract(lut[i].green, LUT_BITS_DEFAULT);
+		hwlut.blue = drm_color_lut_extract(lut[i].blue, LUT_BITS_DEFAULT);
 
 		if (!lut_diff || (i % 2 == 0)) {
-			word = hwlut.red << 20 +
-			       hwlut.green << 10 +
-			       hwlut.red;
+			word = FIELD_PREP(DISP_GAMMA_LUT_10BIT_R, hwlut.red);
+			word |= FIELD_PREP(DISP_GAMMA_LUT_10BIT_G, hwlut.green);
+			word |= FIELD_PREP(DISP_GAMMA_LUT_10BIT_B, hwlut.blue);
 		} else {
 			diff.red = lut[i].red - lut[i - 1].red;
-			diff.red = drm_color_lut_extract(diff.red, 10);
+			diff.red = drm_color_lut_extract(diff.red, LUT_BITS_DEFAULT);
 
 			diff.green = lut[i].green - lut[i - 1].green;
-			diff.green = drm_color_lut_extract(diff.green, 10);
+			diff.green = drm_color_lut_extract(diff.green, LUT_BITS_DEFAULT);
 
 			diff.blue = lut[i].blue - lut[i - 1].blue;
-			diff.blue = drm_color_lut_extract(diff.blue, 10);
+			diff.blue = drm_color_lut_extract(diff.blue, LUT_BITS_DEFAULT);
 
-			word = diff.blue << 20 +
-			       diff.green << 10 +
-			       diff.red;
+			word = FIELD_PREP(DISP_GAMMA_LUT_10BIT_R, diff.red);
+			word |= FIELD_PREP(DISP_GAMMA_LUT_10BIT_G, diff.green);
+			word |= FIELD_PREP(DISP_GAMMA_LUT_10BIT_B, diff.blue);
 		}
 		writel(word, (lut_base + i * 4));
 	}
 
 	/* Enable the gamma table */
-	cfg_val = cfg_val | GAMMA_LUT_EN;
+	cfg_val |= FIELD_PREP(GAMMA_LUT_EN, 1);
 
 	writel(cfg_val, regs + DISP_GAMMA_CFG);
 }
@@ -133,9 +141,12 @@ void mtk_gamma_config(struct device *dev, unsigned int w,
 		      unsigned int bpc, struct cmdq_pkt *cmdq_pkt)
 {
 	struct mtk_disp_gamma *gamma = dev_get_drvdata(dev);
+	u32 sz;
+
+	sz = FIELD_PREP(DISP_GAMMA_SIZE_HSIZE, w);
+	sz |= FIELD_PREP(DISP_GAMMA_SIZE_VSIZE, h);
 
-	mtk_ddp_write(cmdq_pkt, h << 16 | w, &gamma->cmdq_reg, gamma->regs,
-		      DISP_GAMMA_SIZE);
+	mtk_ddp_write(cmdq_pkt, sz, &gamma->cmdq_reg, gamma->regs, DISP_GAMMA_SIZE);
 	if (gamma->data && gamma->data->has_dither)
 		mtk_dither_set_common(gamma->regs, &gamma->cmdq_reg, bpc,
 				      DISP_GAMMA_CFG, GAMMA_DITHERING, cmdq_pkt);
-- 
2.41.0