drm/i915/psr: Enable PSR1 on gen-9+ HW

We have new tests and fixes in place since the feature was last
disabled. Try again for gen-9+ hardware and enable only PSR1 by default as
a first step.
v2: Remove typo fix and comment improvements (Rodrigo)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jose Roberto de Souza <jose.souza@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
References: commit 2ee7dc49 ("drm/i915: disable PSR by default on HSW/BDW")
References: commit dcb2e993 ("Revert "drm/i915: Enable PSR by default on Valleyview and Cherryview."")
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Tested-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180928061117.12394-1-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/intel_psr.c

@@ -71,6 +71,10 @@ static bool psr_global_enabled(u32 debug)
 static bool intel_psr2_enabled(struct drm_i915_private *dev_priv,
 			       const struct intel_crtc_state *crtc_state)
 {
+	/* Disable PSR2 by default for all platforms */
+	if (i915_modparams.enable_psr == -1)
+		return false;
+
 	switch (dev_priv->psr.debug & I915_PSR_DEBUG_MODE_MASK) {
 	case I915_PSR_DEBUG_FORCE_PSR1:
 		return false;
@@ -1066,12 +1070,9 @@ void intel_psr_init(struct drm_i915_private *dev_priv)
 	if (!dev_priv->psr.sink_support)
 		return;
 
-	if (i915_modparams.enable_psr == -1) {
-		i915_modparams.enable_psr = dev_priv->vbt.psr.enable;
-
-		/* Per platform default: all disabled. */
+	if (i915_modparams.enable_psr == -1)
+		if (INTEL_GEN(dev_priv) < 9 || !dev_priv->vbt.psr.enable)
 			i915_modparams.enable_psr = 0;
-	}
 
 	/* Set link_standby x link_off defaults */
 	if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))