drm/i915: add config function for YCBCR420 outputs

This patch checks encoder level support for YCBCR420 outputs.
The logic goes as simple as this:
If the input mode is YCBCR420-only mode: prepare HDMI for
YCBCR420 output, else continue with RGB output mode.

It checks if the mode is YCBCR420 and source can support this
output then it marks the ycbcr_420 output indicator into crtc
state, for further staging in driver.

V2: Split the patch into two, kept helper functions in DRM layer.
V3: Changed the compute_config function based on new DRM API.
V4: Rebase
V5: Rebase
V6: Check and handle YCBCR420-only modes, discard the property
    based approach (Ville)
V7: Addressed review comments from Ville
    - add else case in 12BPC check.
    - extract ycbcr420 state inside hdmi_12bpc_possible function.
V8: Addressed review comments from Ville
    - Remove extra blank lines.
    - Remove "HDMI" from the description of ycbcr420 state variable.
    - Remove local variable, use crtc_state->ycbcr420 instead.
    Added r-b from Ville.
V9: Rebase
V10: Added r-b from Imre

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1500650709-14447-2-git-send-email-shashank.sharma@intel.comSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -10969,6 +10969,7 @@ intel_pipe_config_compare(struct drm_i915_private *dev_priv,
 	PIPE_CONF_CHECK_I(hdmi_scrambling);
 	PIPE_CONF_CHECK_I(hdmi_high_tmds_clock_ratio);
 	PIPE_CONF_CHECK_I(has_infoframe);
+	PIPE_CONF_CHECK_I(ycbcr420);
 
 	PIPE_CONF_CHECK_I(has_audio);
 

drivers/gpu/drm/i915/intel_drv.h

@@ -780,6 +780,9 @@ struct intel_crtc_state {
 
 	/* HDMI High TMDS char rate ratio */
 	bool hdmi_high_tmds_clock_ratio;
+
+	/* output format is YCBCR 4:2:0 */
+	bool ycbcr420;
 };
 
 struct intel_crtc {

drivers/gpu/drm/i915/intel_hdmi.c

@@ -1330,8 +1330,15 @@ static bool hdmi_12bpc_possible(struct intel_crtc_state *crtc_state)
 		if (connector_state->crtc != crtc_state->base.crtc)
 			continue;
 
-		if ((info->edid_hdmi_dc_modes & DRM_EDID_HDMI_DC_36) == 0)
-			return false;
+		if (crtc_state->ycbcr420) {
+			const struct drm_hdmi_info *hdmi = &info->hdmi;
+
+			if (!(hdmi->y420_dc_modes & DRM_EDID_YCBCR420_DC_36))
+				return false;
+		} else {
+			if (!(info->edid_hdmi_dc_modes & DRM_EDID_HDMI_DC_36))
+				return false;
+		}
 	}
 
 	/* Display Wa #1139 */
@@ -1342,6 +1349,24 @@ static bool hdmi_12bpc_possible(struct intel_crtc_state *crtc_state)
 	return true;
 }
 
+static bool
+intel_hdmi_ycbcr420_config(struct drm_connector *connector,
+			   struct intel_crtc_state *config,
+			   int *clock_12bpc, int *clock_8bpc)
+{
+	if (!connector->ycbcr_420_allowed) {
+		DRM_ERROR("Platform doesn't support YCBCR420 output\n");
+		return false;
+	}
+
+	/* YCBCR420 TMDS rate requirement is half the pixel clock */
+	config->port_clock /= 2;
+	*clock_12bpc /= 2;
+	*clock_8bpc /= 2;
+	config->ycbcr420 = true;
+	return true;
+}
+
 bool intel_hdmi_compute_config(struct intel_encoder *encoder,
 			       struct intel_crtc_state *pipe_config,
 			       struct drm_connector_state *conn_state)
@@ -1349,7 +1374,8 @@ bool intel_hdmi_compute_config(struct intel_encoder *encoder,
 	struct intel_hdmi *intel_hdmi = enc_to_intel_hdmi(&encoder->base);
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
-	struct drm_scdc *scdc = &conn_state->connector->display_info.hdmi.scdc;
+	struct drm_connector *connector = conn_state->connector;
+	struct drm_scdc *scdc = &connector->display_info.hdmi.scdc;
 	struct intel_digital_connector_state *intel_conn_state =
 		to_intel_digital_connector_state(conn_state);
 	int clock_8bpc = pipe_config->base.adjusted_mode.crtc_clock;
@@ -1379,6 +1405,14 @@ bool intel_hdmi_compute_config(struct intel_encoder *encoder,
 		clock_12bpc *= 2;
 	}
 
+	if (drm_mode_is_420_only(&connector->display_info, adjusted_mode)) {
+		if (!intel_hdmi_ycbcr420_config(connector, pipe_config,
+						&clock_12bpc, &clock_8bpc)) {
+			DRM_ERROR("Can't support YCBCR420 output\n");
+			return false;
+		}
+	}
+
 	if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv))
 		pipe_config->has_pch_encoder = true;