drm/i915: Clean up HDMI deep color handling a bit

Reogranize the HDMI deep color state computation to just
loop over possible bpc values. Avoids having to maintain
so many variants of the clock etc.

The current code also looks confused w.r.t. port_clock vs.
bw_constrained. It would happily update port_clock for
deep color but then not actually enable deep color due to
bw_constrained being set. The new logic handles that case
correctly.

v2: Pull stuff into separate funcs (Jani)
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190828183424.7856-1-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_hdmi.c

@@ -2265,9 +2265,7 @@ static bool hdmi_deep_color_possible(const struct intel_crtc_state *crtc_state,
 
 static bool
 intel_hdmi_ycbcr420_config(struct drm_connector *connector,
-			   struct intel_crtc_state *config,
-			   int *clock_12bpc, int *clock_10bpc,
-			   int *clock_8bpc)
+			   struct intel_crtc_state *config)
 {
 	struct intel_crtc *intel_crtc = to_intel_crtc(config->base.crtc);
 
@@ -2276,11 +2274,6 @@ intel_hdmi_ycbcr420_config(struct drm_connector *connector,
 		return false;
 	}
 
-	/* YCBCR420 TMDS rate requirement is half the pixel clock */
-	config->port_clock /= 2;
-	*clock_12bpc /= 2;
-	*clock_10bpc /= 2;
-	*clock_8bpc /= 2;
 	config->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
 
 	/* YCBCR 420 output conversion needs a scaler */
@@ -2295,6 +2288,76 @@ intel_hdmi_ycbcr420_config(struct drm_connector *connector,
 	return true;
 }
 
+static int intel_hdmi_port_clock(int clock, int bpc)
+{
+	/*
+	 * Need to adjust the port link by:
+	 *  1.5x for 12bpc
+	 *  1.25x for 10bpc
+	 */
+	return clock * bpc / 8;
+}
+
+static int intel_hdmi_compute_bpc(struct intel_encoder *encoder,
+				  struct intel_crtc_state *crtc_state,
+				  int clock, bool force_dvi)
+{
+	struct intel_hdmi *intel_hdmi = enc_to_intel_hdmi(&encoder->base);
+	int bpc;
+
+	for (bpc = 12; bpc >= 10; bpc -= 2) {
+		if (hdmi_deep_color_possible(crtc_state, bpc) &&
+		    hdmi_port_clock_valid(intel_hdmi,
+					  intel_hdmi_port_clock(clock, bpc),
+					  true, force_dvi) == MODE_OK)
+			return bpc;
+	}
+
+	return 8;
+}
+
+static int intel_hdmi_compute_clock(struct intel_encoder *encoder,
+				    struct intel_crtc_state *crtc_state,
+				    bool force_dvi)
+{
+	struct intel_hdmi *intel_hdmi = enc_to_intel_hdmi(&encoder->base);
+	const struct drm_display_mode *adjusted_mode =
+		&crtc_state->base.adjusted_mode;
+	int bpc, clock = adjusted_mode->crtc_clock;
+
+	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
+		clock *= 2;
+
+	/* YCBCR420 TMDS rate requirement is half the pixel clock */
+	if (crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
+		clock /= 2;
+
+	bpc = intel_hdmi_compute_bpc(encoder, crtc_state,
+				     clock, force_dvi);
+
+	crtc_state->port_clock = intel_hdmi_port_clock(clock, bpc);
+
+	/*
+	 * pipe_bpp could already be below 8bpc due to
+	 * FDI bandwidth constraints. We shouldn't bump it
+	 * back up to 8bpc in that case.
+	 */
+	if (crtc_state->pipe_bpp > bpc * 3)
+		crtc_state->pipe_bpp = bpc * 3;
+
+	DRM_DEBUG_KMS("picking %d bpc for HDMI output (pipe bpp: %d)\n",
+		      bpc, crtc_state->pipe_bpp);
+
+	if (hdmi_port_clock_valid(intel_hdmi, crtc_state->port_clock,
+				  false, force_dvi) != MODE_OK) {
+		DRM_DEBUG_KMS("unsupported HDMI clock (%d kHz), rejecting mode\n",
+			      crtc_state->port_clock);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 int intel_hdmi_compute_config(struct intel_encoder *encoder,
 			      struct intel_crtc_state *pipe_config,
 			      struct drm_connector_state *conn_state)
@@ -2306,11 +2369,8 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
 	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;
-	int clock_10bpc = clock_8bpc * 5 / 4;
-	int clock_12bpc = clock_8bpc * 3 / 2;
-	int desired_bpp;
 	bool force_dvi = intel_conn_state->force_audio == HDMI_AUDIO_OFF_DVI;
+	int ret;
 
 	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		return -EINVAL;
@@ -2332,17 +2392,11 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
 			intel_conn_state->broadcast_rgb == INTEL_BROADCAST_RGB_LIMITED;
 	}
 
-	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK) {
+	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
 		pipe_config->pixel_multiplier = 2;
-		clock_8bpc *= 2;
-		clock_10bpc *= 2;
-		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_10bpc,
-						&clock_8bpc)) {
+		if (!intel_hdmi_ycbcr420_config(connector, pipe_config)) {
 			DRM_ERROR("Can't support YCBCR420 output\n");
 			return -EINVAL;
 		}
@@ -2359,43 +2413,9 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
 				intel_conn_state->force_audio == HDMI_AUDIO_ON;
 	}
 
-	/*
-	 * Note that g4x/vlv don't support 12bpc hdmi outputs. We also need
-	 * to check that the higher clock still fits within limits.
-	 */
-	if (hdmi_deep_color_possible(pipe_config, 12) &&
-	    hdmi_port_clock_valid(intel_hdmi, clock_12bpc,
-				  true, force_dvi) == MODE_OK) {
-		DRM_DEBUG_KMS("picking bpc to 12 for HDMI output\n");
-		desired_bpp = 12*3;
-
-		/* Need to adjust the port link by 1.5x for 12bpc. */
-		pipe_config->port_clock = clock_12bpc;
-	} else if (hdmi_deep_color_possible(pipe_config, 10) &&
-		   hdmi_port_clock_valid(intel_hdmi, clock_10bpc,
-					 true, force_dvi) == MODE_OK) {
-		DRM_DEBUG_KMS("picking bpc to 10 for HDMI output\n");
-		desired_bpp = 10 * 3;
-
-		/* Need to adjust the port link by 1.25x for 10bpc. */
-		pipe_config->port_clock = clock_10bpc;
-	} else {
-		DRM_DEBUG_KMS("picking bpc to 8 for HDMI output\n");
-		desired_bpp = 8*3;
-
-		pipe_config->port_clock = clock_8bpc;
-	}
-
-	if (!pipe_config->bw_constrained) {
-		DRM_DEBUG_KMS("forcing pipe bpp to %i for HDMI\n", desired_bpp);
-		pipe_config->pipe_bpp = desired_bpp;
-	}
-
-	if (hdmi_port_clock_valid(intel_hdmi, pipe_config->port_clock,
-				  false, force_dvi) != MODE_OK) {
-		DRM_DEBUG_KMS("unsupported HDMI clock, rejecting mode\n");
-		return -EINVAL;
-	}
+	ret = intel_hdmi_compute_clock(encoder, pipe_config, force_dvi);
+	if (ret)
+		return ret;
 
 	/* Set user selected PAR to incoming mode's member */
 	adjusted_mode->picture_aspect_ratio = conn_state->picture_aspect_ratio;