drm/i915/dp: make DSC usage logging actually useful

Debug log when DSC is going to be used, and why, instead of
unconditionally logging the rarely used debug option setting, which
might not have any bearing on whether DSC is going to be used or not.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220330093019.4150386-1-jani.nikula@intel.com

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

@@ -1483,6 +1483,7 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 		&pipe_config->hw.adjusted_mode;
 	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
 	struct link_config_limits limits;
+	bool joiner_needs_dsc = false;
 	int ret;
 
 	limits.min_rate = intel_dp_common_rate(intel_dp, 0);
@@ -1518,19 +1519,23 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 				    adjusted_mode->crtc_clock))
 		pipe_config->bigjoiner_pipes = GENMASK(crtc->pipe + 1, crtc->pipe);
 
+	/*
+	 * Pipe joiner needs compression up to display 12 due to bandwidth
+	 * limitation. DG2 onwards pipe joiner can be enabled without
+	 * compression.
+	 */
+	joiner_needs_dsc = DISPLAY_VER(i915) < 13 && pipe_config->bigjoiner_pipes;
+
 	/*
 	 * Optimize for slow and wide for everything, because there are some
 	 * eDP 1.3 and 1.4 panels don't work well with fast and narrow.
 	 */
 	ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config, &limits);
 
-	/*
-	 * Pipe joiner needs compression upto display12 due to BW limitation. DG2
-	 * onwards pipe joiner can be enabled without compression.
-	 */
-	drm_dbg_kms(&i915->drm, "Force DSC en = %d\n", intel_dp->force_dsc_en);
-	if (ret || intel_dp->force_dsc_en ||
-	    (DISPLAY_VER(i915) < 13 && pipe_config->bigjoiner_pipes)) {
+	if (ret || joiner_needs_dsc || intel_dp->force_dsc_en) {
+		drm_dbg_kms(&i915->drm, "Try DSC (fallback=%s, joiner=%s, force=%s)\n",
+			    str_yes_no(ret), str_yes_no(joiner_needs_dsc),
+			    str_yes_no(intel_dp->force_dsc_en));
 		ret = intel_dp_dsc_compute_config(intel_dp, pipe_config,
 						  conn_state, &limits);
 		if (ret < 0)