drm/i915/psr: Avoid DPCD reads when panel does not support PSR

Ville noticed that we are unncessarily reading DPCD's after knowing
panel did not support PSR. Looks like this check that was present
earlier got removed unintentionally, let's put it back.

While we do this, add the PSR version number in the debug print.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NTarun Vyas <tarun.vyas@intel.com>
Reviewed-by: NVathsala Nagaraju <vathsala.nagaraju@intel.com>
Signed-off-by: NDhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180511195145.3829-1-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/intel_psr.c

@@ -246,10 +246,12 @@ void intel_psr_init_dpcd(struct intel_dp *intel_dp)
 	drm_dp_dpcd_read(&intel_dp->aux, DP_PSR_SUPPORT, intel_dp->psr_dpcd,
 			 sizeof(intel_dp->psr_dpcd));
 
-	if (intel_dp->psr_dpcd[0]) {
-		dev_priv->psr.sink_support = true;
-		DRM_DEBUG_KMS("Detected EDP PSR Panel.\n");
-	}
+	if (!intel_dp->psr_dpcd[0])
+		return;
+
+	DRM_DEBUG_KMS("eDP panel supports PSR version %x\n",
+		      intel_dp->psr_dpcd[0]);
+	dev_priv->psr.sink_support = true;
 
 	if (INTEL_GEN(dev_priv) >= 9 &&
 	    (intel_dp->psr_dpcd[0] == DP_PSR2_WITH_Y_COORD_IS_SUPPORTED)) {
@@ -266,8 +268,8 @@ void intel_psr_init_dpcd(struct intel_dp *intel_dp)
 		 */
 		dev_priv->psr.sink_psr2_support =
 				intel_dp_get_y_coord_required(intel_dp);
-		DRM_DEBUG_KMS("PSR2 %s on sink", dev_priv->psr.sink_psr2_support
-			      ? "supported" : "not supported");
+		DRM_DEBUG_KMS("PSR2 %ssupported\n",
+			      dev_priv->psr.sink_psr2_support ? "" : "not ");
 
 		if (dev_priv->psr.sink_psr2_support) {
 			dev_priv->psr.colorimetry_support =