drm: Warn if plane/crtc/encoder/connector index exceeds our 32bit bitmasks

We use 32bit bitmasks to track planes/crtcs/encoders/connectors.
Naturally we can only do that if the index of those objects stays
below 32. Issue a warning whenever we exceed that limit, hopefully
prompting someone to fix the problem.

For connectors the issue is a bit more complicated as they can
be created/destroyed at runtime due to MST. So the problem is no
longer a purely theoretical programmer error. As the connector
indexes are allocated via ida, we can simply limit the maximum
value the ida is allowed to hand out. The error handling is already
in place.

v2: Return an error to the caller (Harry)
v3: Print a debug message so that we know what happened (Maarten)

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180125133020.23845-1-ville.syrjala@linux.intel.com
Reviewed-by: Harry Wentland <harry.wentland@amd.com>

drivers/gpu/drm/drm_connector.c

@@ -205,9 +205,14 @@ int drm_connector_init(struct drm_device *dev,
 	connector->dev = dev;
 	connector->funcs = funcs;
 
-	ret = ida_simple_get(&config->connector_ida, 0, 0, GFP_KERNEL);
-	if (ret < 0)
+	/* connector index is used with 32bit bitmasks */
+	ret = ida_simple_get(&config->connector_ida, 0, 32, GFP_KERNEL);
+	if (ret < 0) {
+		DRM_DEBUG_KMS("Failed to allocate %s connector index: %d\n",
+			      drm_connector_enum_list[connector_type].name,
+			      ret);
 		goto out_put;
+	}
 	connector->index = ret;
 	ret = 0;
 

drivers/gpu/drm/drm_crtc.c

@@ -282,6 +282,10 @@ int drm_crtc_init_with_planes(struct drm_device *dev, struct drm_crtc *crtc,
 	WARN_ON(primary && primary->type != DRM_PLANE_TYPE_PRIMARY);
 	WARN_ON(cursor && cursor->type != DRM_PLANE_TYPE_CURSOR);
 
+	/* crtc index is used with 32bit bitmasks */
+	if (WARN_ON(config->num_crtc >= 32))
+		return -EINVAL;
+
 	crtc->dev = dev;
 	crtc->funcs = funcs;
 

drivers/gpu/drm/drm_encoder.c

@@ -110,6 +110,10 @@ int drm_encoder_init(struct drm_device *dev,
 {
 	int ret;
 
+	/* encoder index is used with 32bit bitmasks */
+	if (WARN_ON(dev->mode_config.num_encoder >= 32))
+		return -EINVAL;
+
 	ret = drm_mode_object_add(dev, &encoder->base, DRM_MODE_OBJECT_ENCODER);
 	if (ret)
 		return ret;

drivers/gpu/drm/drm_plane.c

@@ -173,6 +173,10 @@ int drm_universal_plane_init(struct drm_device *dev, struct drm_plane *plane,
 	unsigned int format_modifier_count = 0;
 	int ret;
 
+	/* plane index is used with 32bit bitmasks */
+	if (WARN_ON(config->num_total_plane >= 32))
+		return -EINVAL;
+
 	ret = drm_mode_object_add(dev, &plane->base, DRM_MODE_OBJECT_PLANE);
 	if (ret)
 		return ret;