drm: add crtc helper drm_crtc_from_index()

It adds a crtc helper drm_crtc_from_index() to find the registered CRTC
with a given index, just like drm_plane_from_index().

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1483015290-16660-2-git-send-email-shawnguo@kernel.org

drivers/gpu/drm/drm_crtc.c

@@ -46,6 +46,26 @@
 #include "drm_crtc_internal.h"
 #include "drm_internal.h"
 
+/**
+ * drm_crtc_from_index - find the registered CRTC at an index
+ * @dev: DRM device
+ * @idx: index of registered CRTC to find for
+ *
+ * Given a CRTC index, return the registered CRTC from DRM device's
+ * list of CRTCs with matching index.
+ */
+struct drm_crtc *drm_crtc_from_index(struct drm_device *dev, int idx)
+{
+	struct drm_crtc *crtc;
+
+	drm_for_each_crtc(crtc, dev)
+		if (idx == crtc->index)
+			return crtc;
+
+	return NULL;
+}
+EXPORT_SYMBOL(drm_crtc_from_index);
+
 /**
  * drm_crtc_force_disable - Forcibly turn off a CRTC
  * @crtc: CRTC to turn off

include/drm/drm_crtc.h

@@ -822,6 +822,7 @@ int drm_crtc_force_disable(struct drm_crtc *crtc);
 int drm_crtc_force_disable_all(struct drm_device *dev);
 
 int drm_mode_set_config_internal(struct drm_mode_set *set);
+struct drm_crtc *drm_crtc_from_index(struct drm_device *dev, int idx);
 
 /* Helpers */
 static inline struct drm_crtc *drm_crtc_find(struct drm_device *dev,