drm/i915/psr: Check if resolution is supported by default SU granularity

Selective updates have a default granularity requirements as stated
by eDP spec(PSR2 SELECTIVE UPDATE X GRANULARITY CAPABILITY register
definition), so check if HW can match those requirements before
enabling PSR2.

v3:
- Changes in the comments and commit message(Dhinakaran)
- Printing the hdisplay that do not match with default granularity

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181204003403.23361-8-jose.souza@intel.com

drivers/gpu/drm/i915/intel_psr.c

@@ -536,6 +536,17 @@ static bool intel_psr2_config_valid(struct intel_dp *intel_dp,
 		return false;
 	}
 
+	/*
+	 * HW sends SU blocks of size four scan lines, which means the starting
+	 * X coordinate and Y granularity requirements will always be met. We
+	 * only need to validate the SU block width is a multiple of 4.
+	 */
+	if (crtc_hdisplay % 4) {
+		DRM_DEBUG_KMS("PSR2 not enabled, hdisplay(%d) not multiple of 4\n",
+			      crtc_hdisplay);
+		return false;
+	}
+
 	return true;
 }