drm/i915/opregion: handle SWSCI Mailbox #2 obsoletion

Opregion Mailbox #2 is obsolete for SWSCI usage in opregion v2.x, and
repurposed in opregion v3.x. Warn about obsole mailbox presence in v2.x,
and ignore with an error for v3.x.

v2: Demote drm_warn() to drm_dbg() on opregion v2.x

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
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/20220210161603.647254-1-jani.nikula@intel.com

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

@@ -932,9 +932,17 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
 	}
 
 	if (mboxes & MBOX_SWSCI) {
-		drm_dbg(&dev_priv->drm, "SWSCI supported\n");
-		opregion->swsci = base + OPREGION_SWSCI_OFFSET;
-		swsci_setup(dev_priv);
+		u8 major = opregion->header->over.major;
+
+		if (major >= 3) {
+			drm_err(&dev_priv->drm, "SWSCI Mailbox #2 present for opregion v3.x, ignoring\n");
+		} else {
+			if (major >= 2)
+				drm_dbg(&dev_priv->drm, "SWSCI Mailbox #2 present for opregion v2.x\n");
+			drm_dbg(&dev_priv->drm, "SWSCI supported\n");
+			opregion->swsci = base + OPREGION_SWSCI_OFFSET;
+			swsci_setup(dev_priv);
+		}
 	}
 
 	if (mboxes & MBOX_ASLE) {