drm/sun4i: frontend: Configure and enable YUV to RGB CSC when needed

In prevision of adding support for YUV formats, set the YUV to RGB
colorspace conversion coefficients if required and don't bypass the
CSC engine when converting.

The BT601 coefficients from the A33 BSP are copied over from the backend
code. Because of module inter-dependency, we can't have the frontend use
these coefficients from the backend directly.
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190118145133.21281-8-paul.kocialkowski@bootlin.com

drivers/gpu/drm/sun4i/sun4i_frontend.c

@@ -213,6 +213,8 @@ int sun4i_frontend_update_formats(struct sun4i_frontend *frontend,
 	const struct drm_format_info *format = fb->format;
 	u32 out_fmt_val;
 	u32 in_fmt_val, in_mod_val, in_ps_val;
+	unsigned int i;
+	u32 bypass;
 	int ret;
 
 	ret = sun4i_frontend_drm_format_to_input_fmt(format, &in_fmt_val);
@@ -250,9 +252,26 @@ int sun4i_frontend_update_formats(struct sun4i_frontend *frontend,
 	regmap_write(frontend->regs, SUN4I_FRONTEND_CH0_VERTPHASE1_REG, 0x400);
 	regmap_write(frontend->regs, SUN4I_FRONTEND_CH1_VERTPHASE1_REG, 0x400);
 
+	/*
+	 * Checking the input format is sufficient since we currently only
+	 * support RGB output formats to the backend. If YUV output formats
+	 * ever get supported, an YUV input and output would require bypassing
+	 * the CSC engine too.
+	 */
+	if (format->is_yuv) {
+		/* Setup the CSC engine for YUV to RGB conversion. */
+		bypass = 0;
+
+		for (i = 0; i < ARRAY_SIZE(sunxi_bt601_yuv2rgb_coef); i++)
+			regmap_write(frontend->regs,
+				     SUN4I_FRONTEND_CSC_COEF_REG(i),
+				     sunxi_bt601_yuv2rgb_coef[i]);
+	} else {
+		bypass = SUN4I_FRONTEND_BYPASS_CSC_EN;
+	}
+
 	regmap_update_bits(frontend->regs, SUN4I_FRONTEND_BYPASS_REG,
-			   SUN4I_FRONTEND_BYPASS_CSC_EN,
-			   SUN4I_FRONTEND_BYPASS_CSC_EN);
+			   SUN4I_FRONTEND_BYPASS_CSC_EN, bypass);
 
 	regmap_write(frontend->regs, SUN4I_FRONTEND_INPUT_FMT_REG,
 		     in_mod_val | in_fmt_val | in_ps_val);

drivers/gpu/drm/sun4i/sun4i_frontend.h

@@ -35,6 +35,8 @@
 #define SUN4I_FRONTEND_OUTPUT_FMT_DATA_FMT_BGRX8888	1
 #define SUN4I_FRONTEND_OUTPUT_FMT_DATA_FMT_XRGB8888	2
 
+#define SUN4I_FRONTEND_CSC_COEF_REG(c)		(0x070 + (0x4 * (c)))
+
 #define SUN4I_FRONTEND_CH0_INSIZE_REG		0x100
 #define SUN4I_FRONTEND_INSIZE(h, w)			((((h) - 1) << 16) | (((w) - 1)))