drm: Add helpers to turn off CRTCs

Turning off a single CRTC or all active CRTCs of a DRM device is a
fairly common pattern. Add helpers to avoid open coding this everywhere.

The name was chosen to be consistent with drm_plane_force_disable().

Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_crtc.c

@@ -396,6 +396,51 @@ void drm_mode_object_reference(struct drm_mode_object *obj)
 }
 EXPORT_SYMBOL(drm_mode_object_reference);
 
+/**
+ * drm_crtc_force_disable - Forcibly turn off a CRTC
+ * @crtc: CRTC to turn off
+ *
+ * Returns:
+ * Zero on success, error code on failure.
+ */
+int drm_crtc_force_disable(struct drm_crtc *crtc)
+{
+	struct drm_mode_set set = {
+		.crtc = crtc,
+	};
+
+	return drm_mode_set_config_internal(&set);
+}
+EXPORT_SYMBOL(drm_crtc_force_disable);
+
+/**
+ * drm_crtc_force_disable_all - Forcibly turn off all enabled CRTCs
+ * @dev: DRM device whose CRTCs to turn off
+ *
+ * Drivers may want to call this on unload to ensure that all displays are
+ * unlit and the GPU is in a consistent, low power state. Takes modeset locks.
+ *
+ * Returns:
+ * Zero on success, error code on failure.
+ */
+int drm_crtc_force_disable_all(struct drm_device *dev)
+{
+	struct drm_crtc *crtc;
+	int ret = 0;
+
+	drm_modeset_lock_all(dev);
+	drm_for_each_crtc(crtc, dev)
+		if (crtc->enabled) {
+			ret = drm_crtc_force_disable(crtc);
+			if (ret)
+				goto out;
+		}
+out:
+	drm_modeset_unlock_all(dev);
+	return ret;
+}
+EXPORT_SYMBOL(drm_crtc_force_disable_all);
+
 static void drm_framebuffer_free(struct kref *kref)
 {
 	struct drm_framebuffer *fb =

include/drm/drm_crtc.h

@@ -2654,6 +2654,8 @@ extern struct drm_plane * drm_plane_from_index(struct drm_device *dev, int idx);
 extern void drm_plane_force_disable(struct drm_plane *plane);
 extern void drm_crtc_get_hv_timing(const struct drm_display_mode *mode,
 				   int *hdisplay, int *vdisplay);
+extern int drm_crtc_force_disable(struct drm_crtc *crtc);
+extern int drm_crtc_force_disable_all(struct drm_device *dev);
 
 extern void drm_encoder_cleanup(struct drm_encoder *encoder);