[PATCH 4/4] drm/bridge: dw-hdmi: Add support for RGB limited range

[Jernej Skrabec]

CEA 861 standard request that RGB quantization range is "limited" for
CEA modes. Support that by adding CSC matrix which downscales values.

This allows to proper color reproduction on TV and PC monitor at the
same time. In future, override property can be added, like "Broadcast
RGB" in i915 driver.

Signed-off-by: Jernej Skrabec <jernej.skrabec at siol.net>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 36 +++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 3d6021119942..101c90156fa0 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -92,6 +92,12 @@ static const u16 csc_coeff_rgb_in_eitu709[3][4] = {
 	{ 0x6756, 0x78ab, 0x2000, 0x0200 }
 };
 
+static const u16 csc_coeff_rgb_limited[3][4] = {
+	{ 0x1B7C, 0x0000, 0x0000, 0x0020 },
+	{ 0x0000, 0x1B7C, 0x0000, 0x0020 },
+	{ 0x0000, 0x0000, 0x1B7C, 0x0020 }
+};
+
 struct hdmi_vmode {
 	bool mdataenablepolarity;
 
@@ -109,6 +115,7 @@ struct hdmi_data_info {
 	unsigned int pix_repet_factor;
 	unsigned int hdcp_enable;
 	struct hdmi_vmode video_mode;
+	bool rgb_limited_range;
 };
 
 struct dw_hdmi_i2c {
@@ -960,6 +967,13 @@ static int is_color_space_conversion(struct dw_hdmi *hdmi)
 		hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_out_bus_format);
 }
 
+static int is_rgb_downscale_needed(struct dw_hdmi *hdmi)
+{
+	return  hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_in_bus_format) &&
+		hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_out_bus_format) &&
+		hdmi->hdmi_data.rgb_limited_range;
+}
+
 static int is_color_space_decimation(struct dw_hdmi *hdmi)
 {
 	if (!hdmi_bus_fmt_is_yuv422(hdmi->hdmi_data.enc_out_bus_format))
@@ -1006,6 +1020,8 @@ static void dw_hdmi_update_csc_coeffs(struct dw_hdmi *hdmi)
 				csc_coeff = &csc_coeff_rgb_in_eitu709;
 			csc_scale = 0;
 		}
+	} else if (is_rgb_downscale_needed(hdmi)) {
+		csc_coeff = &csc_coeff_rgb_limited;
 	}
 
 	/* The CSC registers are sequential, alternating MSB then LSB */
@@ -1615,6 +1631,18 @@ static void hdmi_config_AVI(struct dw_hdmi *hdmi, struct drm_display_mode *mode)
 	drm_hdmi_avi_infoframe_from_display_mode(&frame,
 						 &hdmi->connector, mode);
 
+	if (hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_out_bus_format)) {
+		drm_hdmi_avi_infoframe_quant_range(&frame, &hdmi->connector,
+						   mode,
+						   hdmi->hdmi_data.rgb_limited_range ?
+						   HDMI_QUANTIZATION_RANGE_LIMITED :
+						   HDMI_QUANTIZATION_RANGE_FULL);
+	} else {
+		frame.quantization_range = HDMI_QUANTIZATION_RANGE_DEFAULT;
+		frame.ycc_quantization_range =
+			HDMI_YCC_QUANTIZATION_RANGE_LIMITED;
+	}
+
 	if (hdmi_bus_fmt_is_yuv444(hdmi->hdmi_data.enc_out_bus_format))
 		frame.colorspace = HDMI_COLORSPACE_YUV444;
 	else if (hdmi_bus_fmt_is_yuv422(hdmi->hdmi_data.enc_out_bus_format))
@@ -1990,13 +2018,13 @@ static void dw_hdmi_enable_video_path(struct dw_hdmi *hdmi)
 	hdmi_writeb(hdmi, hdmi->mc_clkdis, HDMI_MC_CLKDIS);
 
 	/* Enable csc path */
-	if (is_color_space_conversion(hdmi)) {
+	if (is_color_space_conversion(hdmi) || is_rgb_downscale_needed(hdmi)) {
 		hdmi->mc_clkdis &= ~HDMI_MC_CLKDIS_CSCCLK_DISABLE;
 		hdmi_writeb(hdmi, hdmi->mc_clkdis, HDMI_MC_CLKDIS);
 	}
 
 	/* Enable color space conversion if needed */
-	if (is_color_space_conversion(hdmi))
+	if (is_color_space_conversion(hdmi) || is_rgb_downscale_needed(hdmi))
 		hdmi_writeb(hdmi, HDMI_MC_FLOWCTRL_FEED_THROUGH_OFF_CSC_IN_PATH,
 			    HDMI_MC_FLOWCTRL);
 	else
@@ -2100,6 +2128,10 @@ static int dw_hdmi_setup(struct dw_hdmi *hdmi, struct drm_display_mode *mode)
 	/* TOFIX: Default to RGB888 output format */
 	hdmi->hdmi_data.enc_out_bus_format = MEDIA_BUS_FMT_RGB888_1X24;
 
+	hdmi->hdmi_data.rgb_limited_range = hdmi->sink_is_hdmi &&
+		drm_default_rgb_quant_range(mode) ==
+		HDMI_QUANTIZATION_RANGE_LIMITED;
+
 	hdmi->hdmi_data.pix_repet_factor = 0;
 	hdmi->hdmi_data.hdcp_enable = 0;
 	hdmi->hdmi_data.video_mode.mdataenablepolarity = true;
-- 
2.25.1