drm/i915/dp: abstract link config selection

For now, there's just the one link config selection, optimizing for slow
and wide link. No functional changes.

Keep the debug logging in the caller, to avoid duplication later on if
alternative link confing selection gets added.

v2: Improved commit message
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/64848b76bf90d6ceecd7ec6b5add28531e0b1a41.1524730974.git.jani.nikula@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -1704,6 +1704,42 @@ static bool intel_edp_compare_alt_mode(struct drm_display_mode *m1,
 	return bres;
 }
 
+/* Optimize link config in order: max bpp, min clock, min lanes */
+static bool
+intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
+				  struct intel_crtc_state *pipe_config,
+				  const struct link_config_limits *limits)
+{
+	struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
+	int bpp, clock, lane_count;
+	int mode_rate, link_clock, link_avail;
+
+	for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 * 3) {
+		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
+						   bpp);
+
+		for (clock = limits->min_clock; clock <= limits->max_clock; clock++) {
+			for (lane_count = limits->min_lane_count;
+			     lane_count <= limits->max_lane_count;
+			     lane_count <<= 1) {
+				link_clock = intel_dp->common_rates[clock];
+				link_avail = intel_dp_max_data_rate(link_clock,
+								    lane_count);
+
+				if (mode_rate <= link_avail) {
+					pipe_config->lane_count = lane_count;
+					pipe_config->pipe_bpp = bpp;
+					pipe_config->port_clock = link_clock;
+
+					return true;
+				}
+			}
+		}
+	}
+
+	return false;
+}
+
 static bool
 intel_dp_compute_link_config(struct intel_encoder *encoder,
 			     struct intel_crtc_state *pipe_config)
@@ -1711,8 +1747,6 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 	struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
 	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
 	struct link_config_limits limits;
-	int bpp, clock, lane_count;
-	int mode_rate, link_avail, link_clock;
 	int common_len;
 
 	common_len = intel_dp_common_len_rate_limit(intel_dp,
@@ -1766,37 +1800,22 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 		      intel_dp->common_rates[limits.max_clock],
 		      limits.max_bpp, adjusted_mode->crtc_clock);
 
-	for (bpp = limits.max_bpp; bpp >= limits.min_bpp; bpp -= 2 * 3) {
-		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
-						   bpp);
-
-		for (clock = limits.min_clock; clock <= limits.max_clock; clock++) {
-			for (lane_count = limits.min_lane_count;
-			     lane_count <= limits.max_lane_count;
-			     lane_count <<= 1) {
-
-				link_clock = intel_dp->common_rates[clock];
-				link_avail = intel_dp_max_data_rate(link_clock,
-								    lane_count);
-
-				if (mode_rate <= link_avail) {
-					goto found;
-				}
-			}
-		}
-	}
-
-	return false;
-
-found:
-	pipe_config->lane_count = lane_count;
-	pipe_config->pipe_bpp = bpp;
-	pipe_config->port_clock = intel_dp->common_rates[clock];
+	/*
+	 * Optimize for slow and wide. This is the place to add alternative
+	 * optimization policy.
+	 */
+	if (!intel_dp_compute_link_config_wide(intel_dp, pipe_config, &limits))
+		return false;
 
 	DRM_DEBUG_KMS("DP lane count %d clock %d bpp %d\n",
-		      pipe_config->lane_count, pipe_config->port_clock, bpp);
-	DRM_DEBUG_KMS("DP link bw required %i available %i\n",
-		      mode_rate, link_avail);
+		      pipe_config->lane_count, pipe_config->port_clock,
+		      pipe_config->pipe_bpp);
+
+	DRM_DEBUG_KMS("DP link rate required %i available %i\n",
+		      intel_dp_link_required(adjusted_mode->crtc_clock,
+					     pipe_config->pipe_bpp),
+		      intel_dp_max_data_rate(pipe_config->port_clock,
+					     pipe_config->lane_count));
 
 	return true;
 }