drm/i915: tell the user KMS is required for gen6+

Educate the users why i915 won't load on gen6+ and nomodeset.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=61671
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1477,8 +1477,11 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	info = (struct intel_device_info *) flags;
 
 	/* Refuse to load on gen6+ without kms enabled. */
-	if (info->gen >= 6 && !drm_core_check_feature(dev, DRIVER_MODESET))
+	if (info->gen >= 6 && !drm_core_check_feature(dev, DRIVER_MODESET)) {
+		DRM_INFO("Your hardware requires kernel modesetting (KMS)\n");
+		DRM_INFO("See CONFIG_DRM_I915_KMS, nomodeset, and i915.modeset parameters\n");
 		return -ENODEV;
+	}
 
 	dev_priv = kzalloc(sizeof(*dev_priv), GFP_KERNEL);
 	if (dev_priv == NULL)