drm/mediatek: set mt8173 dithering function

Some panels only accept bpc (bit per color) 6-bit.
But, the default bpc in mt8173 display data path is 8-bit.
If we didn't enable dithering function to convert bpc,
display cannot show the smooth grayscale image.

In mt8173, the dithering function in OD (OverDrive) and
GAMMA module, we have to config them with
connector->display_mode.bpc when CRTC initial.

1. Clear the default value at *_DITHER_5 and *_DITHER_7 register.
2. Calculate the LSB_ERR_SHIFT bits and ADD_LSHIFT bits two values.
i.e. Input bpc of OD is 10 bits, we assume the bpc of panel is 6-bit,
so, we need to set 4-bit to LSB_ERR_SHIFT and ADD_LSHIFT bits respectively.
3. Then, set the OD or GAMMA to dithering mode depends on path-1 or path-2.

Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

1 files changed, 60 insertions, 12 deletions

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
index 42cd587d6b9b..df33b3ca6ffd 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c
@@ -31,6 +31,10 @@
 #define DISP_OD_INTSTA				0x000c
 #define DISP_OD_CFG				0x0020
 #define DISP_OD_SIZE				0x0030
+#define DISP_DITHER_5				0x0114
+#define DISP_DITHER_7				0x011c
+#define DISP_DITHER_15				0x013c
+#define DISP_DITHER_16				0x0140
 
 #define DISP_REG_UFO_START			0x0000
 
@@ -49,20 +53,59 @@
 
 #define LUT_10BIT_MASK				0x03ff
 
-#define	OD_RELAY_MODE		BIT(0)
+#define COLOR_BYPASS_ALL			BIT(7)
+#define COLOR_SEQ_SEL				BIT(13)
 
-#define	UFO_BYPASS		BIT(2)
+#define OD_RELAYMODE				BIT(0)
 
-#define	COLOR_BYPASS_ALL	BIT(7)
-#define	COLOR_SEQ_SEL		BIT(13)
+#define UFO_BYPASS				BIT(2)
 
-#define AAL_EN			BIT(0)
+#define AAL_EN					BIT(0)
 
-#define GAMMA_EN		BIT(0)
-#define GAMMA_LUT_EN		BIT(1)
+#define GAMMA_EN				BIT(0)
+#define GAMMA_LUT_EN				BIT(1)
+
+#define DISP_DITHERING				BIT(2)
+#define DITHER_LSB_ERR_SHIFT_R(x)		(((x) & 0x7) << 28)
+#define DITHER_OVFLW_BIT_R(x)			(((x) & 0x7) << 24)
+#define DITHER_ADD_LSHIFT_R(x)			(((x) & 0x7) << 20)
+#define DITHER_ADD_RSHIFT_R(x)			(((x) & 0x7) << 16)
+#define DITHER_NEW_BIT_MODE			BIT(0)
+#define DITHER_LSB_ERR_SHIFT_B(x)		(((x) & 0x7) << 28)
+#define DITHER_OVFLW_BIT_B(x)			(((x) & 0x7) << 24)
+#define DITHER_ADD_LSHIFT_B(x)			(((x) & 0x7) << 20)
+#define DITHER_ADD_RSHIFT_B(x)			(((x) & 0x7) << 16)
+#define DITHER_LSB_ERR_SHIFT_G(x)		(((x) & 0x7) << 12)
+#define DITHER_OVFLW_BIT_G(x)			(((x) & 0x7) << 8)
+#define DITHER_ADD_LSHIFT_G(x)			(((x) & 0x7) << 4)
+#define DITHER_ADD_RSHIFT_G(x)			(((x) & 0x7) << 0)
+
+void mtk_dither_set(struct mtk_ddp_comp *comp, unsigned int bpc,
+		    unsigned int CFG)
+{
+	/* If bpc equal to 0, the dithering function didn't be enabled */
+	if (bpc == 0)
+		return;
+
+	if (bpc >= MTK_MIN_BPC) {
+		writel(0, comp->regs + DISP_DITHER_5);
+		writel(0, comp->regs + DISP_DITHER_7);
+		writel(DITHER_LSB_ERR_SHIFT_R(MTK_MAX_BPC - bpc) |
+		       DITHER_ADD_LSHIFT_R(MTK_MAX_BPC - bpc) |
+		       DITHER_NEW_BIT_MODE,
+		       comp->regs + DISP_DITHER_15);
+		writel(DITHER_LSB_ERR_SHIFT_B(MTK_MAX_BPC - bpc) |
+		       DITHER_ADD_LSHIFT_B(MTK_MAX_BPC - bpc) |
+		       DITHER_LSB_ERR_SHIFT_G(MTK_MAX_BPC - bpc) |
+		       DITHER_ADD_LSHIFT_G(MTK_MAX_BPC - bpc),
+		       comp->regs + DISP_DITHER_16);
+		writel(DISP_DITHERING, comp->regs + CFG);
+	}
+}
 
 static void mtk_color_config(struct mtk_ddp_comp *comp, unsigned int w,
-			     unsigned int h, unsigned int vrefresh)
+			     unsigned int h, unsigned int vrefresh,
+			     unsigned int bpc)
 {
 	writel(w, comp->regs + DISP_COLOR_WIDTH);
 	writel(h, comp->regs + DISP_COLOR_HEIGHT);
@@ -76,14 +119,16 @@ static void mtk_color_start(struct mtk_ddp_comp *comp)
 }
 
 static void mtk_od_config(struct mtk_ddp_comp *comp, unsigned int w,
-			  unsigned int h, unsigned int vrefresh)
+			  unsigned int h, unsigned int vrefresh,
+			  unsigned int bpc)
 {
 	writel(w << 16 | h, comp->regs + DISP_OD_SIZE);
+	writel(OD_RELAYMODE, comp->regs + OD_RELAYMODE);
+	mtk_dither_set(comp, bpc, DISP_OD_CFG);
 }
 
 static void mtk_od_start(struct mtk_ddp_comp *comp)
 {
-	writel(OD_RELAY_MODE, comp->regs + DISP_OD_CFG);
 	writel(1, comp->regs + DISP_OD_EN);
 }
 
@@ -93,7 +138,8 @@ static void mtk_ufoe_start(struct mtk_ddp_comp *comp)
 }
 
 static void mtk_aal_config(struct mtk_ddp_comp *comp, unsigned int w,
-			   unsigned int h, unsigned int vrefresh)
+			   unsigned int h, unsigned int vrefresh,
+			   unsigned int bpc)
 {
 	writel(h << 16 | w, comp->regs + DISP_AAL_SIZE);
 }
@@ -109,9 +155,11 @@ static void mtk_aal_stop(struct mtk_ddp_comp *comp)
 }
 
 static void mtk_gamma_config(struct mtk_ddp_comp *comp, unsigned int w,
-			     unsigned int h, unsigned int vrefresh)
+			     unsigned int h, unsigned int vrefresh,
+			     unsigned int bpc)
 {
 	writel(h << 16 | w, comp->regs + DISP_GAMMA_SIZE);
+	mtk_dither_set(comp, bpc, DISP_GAMMA_CFG);
 }
 
 static void mtk_gamma_start(struct mtk_ddp_comp *comp)