weston: Port DRM backend to new output handling API

This is a complete port of the DRM backend that uses
the recently added output handling API for output
configuration.

Output can be configured at runtime by passing the
necessary configuration parameters, which can be
filled in manually or obtained from the configuration
file using previously added functionality. It is
required that the scale and transform values are set
using the previously added functionality.

After everything has been set, output needs to be
enabled manually using weston_output_enable().

v2:

 - Added missing drmModeFreeCrtc() to drm_output_enable()
   cleanup list in case of failure.
 - Split drm_backend_disable() into drm_backend_deinit()
   to accomodate for changes in the first patch in the
   series. Moved restoring original crtc to
   drm_output_destroy().

v3:

 - Moved origcrtc allocation to drm_output_set_mode().
 - Swapped connector_get_current_mode() and
   drm_output_add_mode() calls in drm_output_set_mode()
   to match current weston.
 - Moved crtc_allocator and connector_allocator update
   from drm_output_enable() to create_output_for_connector()
   to avoid problems when more than one monitor is connected
   at startup and crtc allocator wasn't updated before
   create_output_for_connector() was called second time,
   resulting in one screen being turned off.
 - Moved crtc_allocator and connector_allocator update from
   drm_output_deinit() to drm_output_destroy(), as it
   should not be called on drm_output_disable().
 - Use weston_compositor_add_pending_output().
 - Bump weston_drm_backend_config version to 2.

v4:

 - Reset output->original_crtc to NULL if drm_output_set_mode()
   fails.
 - Remove unneeded log message when disabling an output when a
   pageflip is pending.
 - Document that create_output_for_connector() takes ownership
   of the connector.
 - Free the connector if create output conditionals are not met
   in create_outputs() and update_outputs().

Signed-off-by: Armin Krezović <krezovic.armin@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

3 files changed, 348 insertions, 245 deletions

diff --git a/compositor/main.c b/compositor/main.c
index 0cc11a5e..38df77f6 100644
--- a/compositor/main.c
+++ b/compositor/main.c
@@ -1087,48 +1087,6 @@ wet_configure_windowed_output_from_config(struct weston_output *output,
 	return 0;
 }
 
-static enum weston_drm_backend_output_mode
-drm_configure_output(struct weston_compositor *c,
-		     bool use_current_mode,
-		     const char *name,
-		     struct weston_drm_backend_output_config *config)
-{
-	struct weston_config *wc = wet_get_config(c);
-	struct weston_config_section *section;
-	char *s;
-	int scale;
-	enum weston_drm_backend_output_mode mode =
-		WESTON_DRM_BACKEND_OUTPUT_PREFERRED;
-
-	section = weston_config_get_section(wc, "output", "name", name);
-	weston_config_section_get_string(section, "mode", &s, "preferred");
-	if (strcmp(s, "off") == 0) {
-		free(s);
-		return WESTON_DRM_BACKEND_OUTPUT_OFF;
-	}
-
-	if (use_current_mode || strcmp(s, "current") == 0) {
-		mode = WESTON_DRM_BACKEND_OUTPUT_CURRENT;
-	} else if (strcmp(s, "preferred") != 0) {
-		config->modeline = s;
-		s = NULL;
-	}
-	free(s);
-
-	weston_config_section_get_int(section, "scale", &scale, 1);
-	config->base.scale = scale >= 1 ? scale : 1;
-	weston_config_section_get_string(section, "transform", &s, "normal");
-	if (weston_parse_transform(s, &config->base.transform) < 0)
-		weston_log("Invalid transform \"%s\" for output %s\n",
-			   s, name);
-	free(s);
-
-	weston_config_section_get_string(section,
-					 "gbm-format", &config->gbm_format, NULL);
-	weston_config_section_get_string(section, "seat", &config->seat, "");
-	return mode;
-}
-
 static void
 configure_input_device(struct weston_compositor *compositor,
 		       struct libinput_device *device)
@@ -1153,6 +1111,65 @@ configure_input_device(struct weston_compositor *compositor,
 	}
 }
 
+static void
+drm_backend_output_configure(struct wl_listener *listener, void *data)
+{
+	struct weston_output *output = data;
+	struct weston_config *wc = wet_get_config(output->compositor);
+	struct weston_config_section *section;
+	const struct weston_drm_output_api *api = weston_drm_output_get_api(output->compositor);
+	enum weston_drm_backend_output_mode mode =
+		WESTON_DRM_BACKEND_OUTPUT_PREFERRED;
+
+	char *s;
+	char *modeline = NULL;
+	char *gbm_format = NULL;
+	char *seat = NULL;
+
+	if (!api) {
+		weston_log("Cannot use weston_drm_output_api.\n");
+		return;
+	}
+
+	section = weston_config_get_section(wc, "output", "name", output->name);
+	weston_config_section_get_string(section, "mode", &s, "preferred");
+
+	if (strcmp(s, "off") == 0) {
+		weston_output_disable(output);
+		free(s);
+		return;
+	} else if (strcmp(s, "current") == 0) {
+		mode = WESTON_DRM_BACKEND_OUTPUT_CURRENT;
+	} else if (strcmp(s, "preferred") != 0) {
+		modeline = s;
+		s = NULL;
+	}
+	free(s);
+
+	if (api->set_mode(output, mode, modeline) < 0) {
+		weston_log("Cannot configure an output using weston_drm_output_api.\n");
+		free(modeline);
+		return;
+	}
+	free(modeline);
+
+	wet_output_set_scale(output, section, 1, 0);
+	wet_output_set_transform(output, section, WL_OUTPUT_TRANSFORM_NORMAL, UINT32_MAX);
+
+	weston_config_section_get_string(section,
+					 "gbm-format", &gbm_format, NULL);
+
+	api->set_gbm_format(output, gbm_format);
+	free(gbm_format);
+
+	weston_config_section_get_string(section, "seat", &seat, "");
+
+	api->set_seat(output, seat);
+	free(seat);
+
+	weston_output_enable(output);
+}
+
 static int
 load_drm_backend(struct weston_compositor *c,
 		 int *argc, char **argv, struct weston_config *wc)
@@ -1178,12 +1195,13 @@ load_drm_backend(struct weston_compositor *c,
 
 	config.base.struct_version = WESTON_DRM_BACKEND_CONFIG_VERSION;
 	config.base.struct_size = sizeof(struct weston_drm_backend_config);
-	config.configure_output = drm_configure_output;
 	config.configure_device = configure_input_device;
 
 	ret = weston_compositor_load_backend(c, WESTON_BACKEND_DRM,
 					     &config.base);
 
+	wet_set_pending_output_handler(c, drm_backend_output_configure);
+
 	free(config.gbm_format);
 	free(config.seat_id);
 
diff --git a/libweston/compositor-drm.c b/libweston/compositor-drm.c
index 8319d7cf..491f171f 100644
--- a/libweston/compositor-drm.c
+++ b/libweston/compositor-drm.c
@@ -122,16 +122,6 @@ struct drm_backend {
 	int32_t cursor_width;
 	int32_t cursor_height;
 
-        /** Callback used to configure the outputs.
-	 *
-         * This function will be called by the backend when a new DRM
-         * output needs to be configured.
-         */
-        enum weston_drm_backend_output_mode
-	(*configure_output)(struct weston_compositor *compositor,
-			    bool use_current_mode,
-			    const char *name,
-			    struct weston_drm_backend_output_config *output_config);
 	bool use_current_mode;
 };
 
@@ -161,7 +151,8 @@ struct drm_edid {
 };
 
 struct drm_output {
-	struct weston_output   base;
+	struct weston_output base;
+	drmModeConnector *connector;
 
 	uint32_t crtc_id;
 	int pipe;
@@ -176,6 +167,7 @@ struct drm_output {
 	int vblank_pending;
 	int page_flip_pending;
 	int destroy_pending;
+	int disable_pending;
 
 	struct gbm_surface *gbm_surface;
 	struct gbm_bo *gbm_cursor_bo[2];
@@ -681,7 +673,7 @@ drm_output_repaint(struct weston_output *output_base,
 	struct drm_mode *mode;
 	int ret = 0;
 
-	if (output->destroy_pending)
+	if (output->disable_pending || output->destroy_pending)
 		return -1;
 
 	if (!output->next)
@@ -787,7 +779,7 @@ drm_output_start_repaint_loop(struct weston_output *output_base)
 		.request.signal = 0,
 	};
 
-	if (output->destroy_pending)
+	if (output->disable_pending || output->destroy_pending)
 		return;
 
 	if (!output->current) {
@@ -877,7 +869,7 @@ vblank_handler(int fd, unsigned int frame, unsigned int sec, unsigned int usec,
 }
 
 static void
-drm_output_destroy(struct weston_output *output_base);
+drm_output_destroy(struct weston_output *base);
 
 static void
 page_flip_handler(int fd, unsigned int frame,
@@ -904,6 +896,8 @@ page_flip_handler(int fd, unsigned int frame,
 
 	if (output->destroy_pending)
 		drm_output_destroy(&output->base);
+	else if (output->disable_pending)
+		weston_output_disable(&output->base);
 	else if (!output->vblank_pending) {
 		ts.tv_sec = sec;
 		ts.tv_nsec = usec * 1000;
@@ -1344,51 +1338,6 @@ drm_assign_planes(struct weston_output *output_base)
 static void
 drm_output_fini_pixman(struct drm_output *output);
 
-static void
-drm_output_destroy(struct weston_output *output_base)
-{
-	struct drm_output *output = to_drm_output(output_base);
-	struct drm_backend *b = to_drm_backend(output->base.compositor);
-	drmModeCrtcPtr origcrtc = output->original_crtc;
-
-	if (output->page_flip_pending) {
-		output->destroy_pending = 1;
-		weston_log("destroy output while page flip pending\n");
-		return;
-	}
-
-	if (output->backlight)
-		backlight_destroy(output->backlight);
-
-	drmModeFreeProperty(output->dpms_prop);
-
-	/* Turn off hardware cursor */
-	drmModeSetCursor(b->drm.fd, output->crtc_id, 0, 0, 0);
-
-	/* Restore original CRTC state */
-	drmModeSetCrtc(b->drm.fd, origcrtc->crtc_id, origcrtc->buffer_id,
-		       origcrtc->x, origcrtc->y,
-		       &output->connector_id, 1, &origcrtc->mode);
-	drmModeFreeCrtc(origcrtc);
-
-	b->crtc_allocator &= ~(1 << output->crtc_id);
-	b->connector_allocator &= ~(1 << output->connector_id);
-
-	if (b->use_pixman) {
-		drm_output_fini_pixman(output);
-	} else {
-		gl_renderer->output_destroy(output_base);
-		gbm_surface_destroy(output->gbm_surface);
-	}
-
-	weston_plane_release(&output->fb_plane);
-	weston_plane_release(&output->cursor_plane);
-
-	weston_output_destroy(&output->base);
-
-	free(output);
-}
-
 /**
  * Find the closest-matching mode for a given target
  *
@@ -2239,7 +2188,7 @@ static struct drm_mode *
 drm_output_choose_initial_mode(struct drm_backend *backend,
 			       struct drm_output *output,
 			       enum weston_drm_backend_output_mode mode,
-			       struct weston_drm_backend_output_config *config,
+			       const char *modeline,
 			       const drmModeModeInfo *current_mode)
 {
 	struct drm_mode *preferred = NULL;
@@ -2247,21 +2196,21 @@ drm_output_choose_initial_mode(struct drm_backend *backend,
 	struct drm_mode *configured = NULL;
 	struct drm_mode *best = NULL;
 	struct drm_mode *drm_mode;
-	drmModeModeInfo modeline;
+	drmModeModeInfo drm_modeline;
 	int32_t width = 0;
 	int32_t height = 0;
 
-	if (mode == WESTON_DRM_BACKEND_OUTPUT_PREFERRED && config->modeline) {
-		if (sscanf(config->modeline, "%dx%d", &width, &height) != 2) {
+	if (mode == WESTON_DRM_BACKEND_OUTPUT_PREFERRED && modeline) {
+		if (sscanf(modeline, "%dx%d", &width, &height) != 2) {
 			width = -1;
 
-			if (parse_modeline(config->modeline, &modeline) == 0) {
-				configured = drm_output_add_mode(output, &modeline);
+			if (parse_modeline(modeline, &drm_modeline) == 0) {
+				configured = drm_output_add_mode(output, &drm_modeline);
 				if (!configured)
 					return NULL;
 			} else {
 				weston_log("Invalid modeline \"%s\" for output %s\n",
-					   config->modeline, output->base.name);
+					   modeline, output->base.name);
 			}
 		}
 	}
@@ -2330,109 +2279,104 @@ connector_get_current_mode(drmModeConnector *connector, int drm_fd,
 	return 0;
 }
 
-/**
- * Create and configure a Weston output structure
- *
- * Given a DRM connector, create a matching drm_output structure and add it
- * to Weston's output list.
- *
- * @param b Weston backend structure structure
- * @param resources DRM resources for this device
- * @param connector DRM connector to use for this new output
- * @param x Horizontal offset to use into global co-ordinate space
- * @param y Vertical offset to use into global co-ordinate space
- * @param drm_device udev device pointer
- * @returns 0 on success, or -1 on failure
- */
 static int
-create_output_for_connector(struct drm_backend *b,
-			    drmModeRes *resources,
-			    drmModeConnector *connector,
-			    int x, int y, struct udev_device *drm_device)
+drm_output_set_mode(struct weston_output *base,
+		    enum weston_drm_backend_output_mode mode,
+		    const char *modeline)
 {
-	struct drm_output *output;
-	struct drm_mode *drm_mode, *next, *current;
-	struct weston_mode *m;
+	struct drm_output *output = to_drm_output(base);
+	struct drm_backend *b = to_drm_backend(base->compositor);
 
+	struct drm_mode *drm_mode, *next, *current;
 	drmModeModeInfo crtc_mode;
 	int i;
-	enum weston_drm_backend_output_mode mode;
-	struct weston_drm_backend_output_config config = {{ 0 }};
 
-	i = find_crtc_for_connector(b, resources, connector);
-	if (i < 0) {
-		weston_log("No usable crtc/encoder pair for connector.\n");
-		return -1;
-	}
-
-	output = zalloc(sizeof *output);
-	if (output == NULL)
-		return -1;
-
-	output->base.subpixel = drm_subpixel_to_wayland(connector->subpixel);
-	output->base.name = make_connector_name(connector);
 	output->base.make = "unknown";
 	output->base.model = "unknown";
 	output->base.serial_number = "unknown";
 	wl_list_init(&output->base.mode_list);
 
-	mode = b->configure_output(b->compositor, b->use_current_mode,
-				   output->base.name, &config);
-	if (parse_gbm_format(config.gbm_format, b->gbm_format, &output->gbm_format) == -1)
-		output->gbm_format = b->gbm_format;
-
-	setup_output_seat_constraint(b, &output->base,
-				     config.seat ? config.seat : "");
-	free(config.seat);
-
-	output->crtc_id = resources->crtcs[i];
-	output->pipe = i;
-	b->crtc_allocator |= (1 << output->crtc_id);
-	output->connector_id = connector->connector_id;
-	b->connector_allocator |= (1 << output->connector_id);
-
 	output->original_crtc = drmModeGetCrtc(b->drm.fd, output->crtc_id);
-	output->dpms_prop = drm_get_prop(b->drm.fd, connector, "DPMS");
 
-	if (connector_get_current_mode(connector, b->drm.fd, &crtc_mode) < 0)
+	if (connector_get_current_mode(output->connector, b->drm.fd, &crtc_mode) < 0)
 		goto err_free;
 
-	for (i = 0; i < connector->count_modes; i++) {
-		drm_mode = drm_output_add_mode(output, &connector->modes[i]);
+	for (i = 0; i < output->connector->count_modes; i++) {
+		drm_mode = drm_output_add_mode(output, &output->connector->modes[i]);
 		if (!drm_mode)
 			goto err_free;
 	}
 
-	if (mode == WESTON_DRM_BACKEND_OUTPUT_OFF) {
-		weston_log("Disabling output %s\n", output->base.name);
-		drmModeSetCrtc(b->drm.fd, output->crtc_id,
-			       0, 0, 0, 0, 0, NULL);
-		goto err_free;
-	}
-
-	current = drm_output_choose_initial_mode(b, output, mode, &config,
-						 &crtc_mode);
+	current = drm_output_choose_initial_mode(b, output, mode, modeline, &crtc_mode);
 	if (!current)
 		goto err_free;
+
 	output->base.current_mode = &current->base;
 	output->base.current_mode->flags |= WL_OUTPUT_MODE_CURRENT;
 
-	weston_output_init(&output->base, b->compositor, x, y,
-			   connector->mmWidth, connector->mmHeight,
-			   config.base.transform, config.base.scale);
+	/* Set native_ fields, so weston_output_mode_switch_to_native() works */
+	output->base.native_mode = output->base.current_mode;
+	output->base.native_scale = output->base.current_scale;
+
+	output->base.mm_width = output->connector->mmWidth;
+	output->base.mm_height = output->connector->mmHeight;
+
+	return 0;
+
+err_free:
+	drmModeFreeCrtc(output->original_crtc);
+	output->original_crtc = NULL;
+
+	wl_list_for_each_safe(drm_mode, next, &output->base.mode_list,
+							base.link) {
+		wl_list_remove(&drm_mode->base.link);
+		free(drm_mode);
+	}
+
+	return -1;
+}
+
+static void
+drm_output_set_gbm_format(struct weston_output *base,
+			  const char *gbm_format)
+{
+	struct drm_output *output = to_drm_output(base);
+	struct drm_backend *b = to_drm_backend(base->compositor);
+
+	if (parse_gbm_format(gbm_format, b->gbm_format, &output->gbm_format) == -1)
+		output->gbm_format = b->gbm_format;
+}
+
+static void
+drm_output_set_seat(struct weston_output *base,
+		    const char *seat)
+{
+	struct drm_output *output = to_drm_output(base);
+	struct drm_backend *b = to_drm_backend(base->compositor);
+
+	setup_output_seat_constraint(b, &output->base,
+				     seat ? seat : "");
+}
+
+static int
+drm_output_enable(struct weston_output *base)
+{
+	struct drm_output *output = to_drm_output(base);
+	struct drm_backend *b = to_drm_backend(base->compositor);
+	struct weston_mode *m;
+
+	output->dpms_prop = drm_get_prop(b->drm.fd, output->connector, "DPMS");
 
 	if (b->use_pixman) {
 		if (drm_output_init_pixman(output, b) < 0) {
 			weston_log("Failed to init output pixman state\n");
-			goto err_output;
+			goto err_free;
 		}
 	} else if (drm_output_init_egl(output, b) < 0) {
 		weston_log("Failed to init output gl state\n");
-		goto err_output;
+		goto err_free;
 	}
 
-	output->backlight = backlight_init(drm_device,
-					   connector->connector_type);
 	if (output->backlight) {
 		weston_log("Initialized backlight, device %s\n",
 			   output->backlight->path);
@@ -2442,15 +2386,8 @@ create_output_for_connector(struct drm_backend *b,
 		weston_log("Failed to initialize backlight\n");
 	}
 
-	weston_compositor_add_output(b->compositor, &output->base);
-
-	find_and_parse_output_edid(b, output, connector);
-	if (connector->connector_type == DRM_MODE_CONNECTOR_LVDS)
-		output->base.connection_internal = 1;
-
 	output->base.start_repaint_loop = drm_output_start_repaint_loop;
 	output->base.repaint = drm_output_repaint;
-	output->base.destroy = drm_output_destroy;
 	output->base.assign_planes = drm_assign_planes;
 	output->base.set_dpms = drm_set_dpms;
 	output->base.switch_mode = drm_output_switch_mode;
@@ -2458,6 +2395,12 @@ create_output_for_connector(struct drm_backend *b,
 	output->base.gamma_size = output->original_crtc->gamma_size;
 	output->base.set_gamma = drm_output_set_gamma;
 
+	output->base.subpixel = drm_subpixel_to_wayland(output->connector->subpixel);
+
+	find_and_parse_output_edid(b, output, output->connector);
+	if (output->connector->connector_type == DRM_MODE_CONNECTOR_LVDS)
+		output->base.connection_internal = 1;
+
 	weston_plane_init(&output->cursor_plane, b->compositor,
 			  INT32_MIN, INT32_MIN);
 	weston_plane_init(&output->fb_plane, b->compositor, 0, 0);
@@ -2475,31 +2418,155 @@ create_output_for_connector(struct drm_backend *b,
 				    ", preferred" : "",
 				    m->flags & WL_OUTPUT_MODE_CURRENT ?
 				    ", current" : "",
-				    connector->count_modes == 0 ?
+				    output->connector->count_modes == 0 ?
 				    ", built-in" : "");
 
-	/* Set native_ fields, so weston_output_mode_switch_to_native() works */
-	output->base.native_mode = output->base.current_mode;
-	output->base.native_scale = output->base.current_scale;
-
 	return 0;
 
-err_output:
-	weston_output_destroy(&output->base);
 err_free:
-	wl_list_for_each_safe(drm_mode, next, &output->base.mode_list,
-							base.link) {
-		wl_list_remove(&drm_mode->base.link);
-		free(drm_mode);
+	drmModeFreeProperty(output->dpms_prop);
+
+	return -1;
+}
+
+static void
+drm_output_deinit(struct weston_output *base)
+{
+	struct drm_output *output = to_drm_output(base);
+	struct drm_backend *b = to_drm_backend(base->compositor);
+
+	if (b->use_pixman) {
+		drm_output_fini_pixman(output);
+	} else {
+		gl_renderer->output_destroy(&output->base);
+		gbm_surface_destroy(output->gbm_surface);
 	}
 
-	drmModeFreeCrtc(output->original_crtc);
+	weston_plane_release(&output->fb_plane);
+	weston_plane_release(&output->cursor_plane);
+
+	drmModeFreeProperty(output->dpms_prop);
+
+	/* Turn off hardware cursor */
+	drmModeSetCursor(b->drm.fd, output->crtc_id, 0, 0, 0);
+}
+
+static void
+drm_output_destroy(struct weston_output *base)
+{
+	struct drm_output *output = to_drm_output(base);
+	struct drm_backend *b = to_drm_backend(base->compositor);
+	drmModeCrtcPtr origcrtc = output->original_crtc;
+
+	if (output->page_flip_pending) {
+		output->destroy_pending = 1;
+		weston_log("destroy output while page flip pending\n");
+		return;
+	}
+
+	if (output->base.enabled)
+		drm_output_deinit(&output->base);
+
+	if (origcrtc) {
+		/* Restore original CRTC state */
+		drmModeSetCrtc(b->drm.fd, origcrtc->crtc_id, origcrtc->buffer_id,
+			       origcrtc->x, origcrtc->y,
+			       &output->connector_id, 1, &origcrtc->mode);
+		drmModeFreeCrtc(origcrtc);
+	}
+
+	weston_output_destroy(&output->base);
+
+	drmModeFreeConnector(output->connector);
+
+	if (output->backlight)
+		backlight_destroy(output->backlight);
+
 	b->crtc_allocator &= ~(1 << output->crtc_id);
 	b->connector_allocator &= ~(1 << output->connector_id);
+
 	free(output);
-	free(config.modeline);
+}
 
-	return -1;
+static int
+drm_output_disable(struct weston_output *base)
+{
+	struct drm_output *output = to_drm_output(base);
+	struct drm_backend *b = to_drm_backend(base->compositor);
+
+	if (output->page_flip_pending) {
+		output->disable_pending = 1;
+		return -1;
+	}
+
+	if (output->base.enabled)
+		drm_output_deinit(&output->base);
+
+	output->disable_pending = 0;
+
+	weston_log("Disabling output %s\n", output->base.name);
+	drmModeSetCrtc(b->drm.fd, output->crtc_id,
+		       0, 0, 0, 0, 0, NULL);
+
+	return 0;
+}
+
+/**
+ * Create a Weston output structure
+ *
+ * Given a DRM connector, create a matching drm_output structure and add it
+ * to Weston's output list. It also takes ownership of the connector, which
+ * is released when output is destroyed.
+ *
+ * @param b Weston backend structure
+ * @param resources DRM resources for this device
+ * @param connector DRM connector to use for this new output
+ * @param drm_device udev device pointer
+ * @returns 0 on success, or -1 on failure
+ */
+static int
+create_output_for_connector(struct drm_backend *b,
+			    drmModeRes *resources,
+			    drmModeConnector *connector,
+			    struct udev_device *drm_device)
+{
+	struct drm_output *output;
+	int i;
+
+	i = find_crtc_for_connector(b, resources, connector);
+	if (i < 0) {
+		weston_log("No usable crtc/encoder pair for connector.\n");
+		return -1;
+	}
+
+	output = zalloc(sizeof *output);
+	if (output == NULL)
+		return -1;
+
+	output->connector = connector;
+	output->crtc_id = resources->crtcs[i];
+	output->pipe = i;
+	output->connector_id = connector->connector_id;
+
+	output->backlight = backlight_init(drm_device,
+					   connector->connector_type);
+
+	output->base.enable = drm_output_enable;
+	output->base.destroy = drm_output_destroy;
+	output->base.disable = drm_output_disable;
+	output->base.name = make_connector_name(connector);
+
+	output->destroy_pending = 0;
+	output->disable_pending = 0;
+	output->original_crtc = NULL;
+
+	b->crtc_allocator |= (1 << output->crtc_id);
+	b->connector_allocator |= (1 << output->connector_id);
+
+	weston_output_init_pending(&output->base, b->compositor);
+	weston_compositor_add_pending_output(&output->base, b->compositor);
+
+	return 0;
 }
 
 static void
@@ -2578,7 +2645,6 @@ create_outputs(struct drm_backend *b, uint32_t option_connector,
 	drmModeConnector *connector;
 	drmModeRes *resources;
 	int i;
-	int x = 0, y = 0;
 
 	resources = drmModeGetResources(b->drm.fd);
 	if (!resources) {
@@ -2610,21 +2676,17 @@ create_outputs(struct drm_backend *b, uint32_t option_connector,
 		    (option_connector == 0 ||
 		     connector->connector_id == option_connector)) {
 			if (create_output_for_connector(b, resources,
-							connector, x, y,
-							drm_device) < 0) {
+							connector, drm_device) < 0) {
 				drmModeFreeConnector(connector);
 				continue;
 			}
-
-			x += container_of(b->compositor->output_list.prev,
-					  struct weston_output,
-					  link)->width;
+		} else {
+			drmModeFreeConnector(connector);
 		}
-
-		drmModeFreeConnector(connector);
 	}
 
-	if (wl_list_empty(&b->compositor->output_list))
+	if (wl_list_empty(&b->compositor->output_list) &&
+	    wl_list_empty(&b->compositor->pending_output_list))
 		weston_log("No currently active connector found.\n");
 
 	drmModeFreeResources(resources);
@@ -2638,7 +2700,6 @@ update_outputs(struct drm_backend *b, struct udev_device *drm_device)
 	drmModeConnector *connector;
 	drmModeRes *resources;
 	struct drm_output *output, *next;
-	int x = 0, y = 0;
 	uint32_t connected = 0, disconnects = 0;
 	int i;
 
@@ -2664,23 +2725,13 @@ update_outputs(struct drm_backend *b, struct udev_device *drm_device)
 		connected |= (1 << connector_id);
 
 		if (!(b->connector_allocator & (1 << connector_id))) {
-			struct weston_output *last =
-				container_of(b->compositor->output_list.prev,
-					     struct weston_output, link);
-
-			/* XXX: not yet needed, we die with 0 outputs */
-			if (!wl_list_empty(&b->compositor->output_list))
-				x = last->x + last->width;
-			else
-				x = 0;
-			y = 0;
 			create_output_for_connector(b, resources,
-						    connector, x, y,
-						    drm_device);
+						    connector, drm_device);
 			weston_log("connector %d connected\n", connector_id);
 
+		} else {
+			drmModeFreeConnector(connector);
 		}
-		drmModeFreeConnector(connector);
 	}
 	drmModeFreeResources(resources);
 
@@ -2695,6 +2746,16 @@ update_outputs(struct drm_backend *b, struct udev_device *drm_device)
 				drm_output_destroy(&output->base);
 			}
 		}
+
+		wl_list_for_each_safe(output, next, &b->compositor->pending_output_list,
+				      base.link) {
+			if (disconnects & (1 << output->connector_id)) {
+				disconnects &= ~(1 << output->connector_id);
+				weston_log("connector %d disconnected\n",
+				       output->connector_id);
+				drm_output_destroy(&output->base);
+			}
+		}
 	}
 }
 
@@ -3078,6 +3139,12 @@ renderer_switch_binding(struct weston_keyboard *keyboard, uint32_t time,
 	switch_to_gl_renderer(b);
 }
 
+static const struct weston_drm_output_api api = {
+	drm_output_set_mode,
+	drm_output_set_gbm_format,
+	drm_output_set_seat,
+};
+
 static struct drm_backend *
 drm_backend_create(struct weston_compositor *compositor,
 		   struct weston_drm_backend_config *config)
@@ -3087,6 +3154,7 @@ drm_backend_create(struct weston_compositor *compositor,
 	struct wl_event_loop *loop;
 	const char *path;
 	const char *seat_id = default_seat;
+	int ret;
 
 	weston_log("initializing drm backend\n");
 
@@ -3107,7 +3175,6 @@ drm_backend_create(struct weston_compositor *compositor,
 	b->sprites_are_broken = 1;
 	b->compositor = compositor;
 	b->use_pixman = config->use_pixman;
-	b->configure_output = config->configure_output;
 	b->use_current_mode = config->use_current_mode;
 
 	if (parse_gbm_format(config->gbm_format, GBM_FORMAT_XRGB8888, &b->gbm_format) < 0)
@@ -3230,6 +3297,14 @@ drm_backend_create(struct weston_compositor *compositor,
 
 	compositor->backend = &b->base;
 
+	ret = weston_plugin_api_register(compositor, WESTON_DRM_OUTPUT_API_NAME,
+					 &api, sizeof(api));
+
+	if (ret < 0) {
+		weston_log("Failed to register output API.\n");
+		goto err_udev_monitor;
+	}
+
 	return b;
 
 err_udev_monitor:
diff --git a/libweston/compositor-drm.h b/libweston/compositor-drm.h
index 1266031f..8f89a2b3 100644
--- a/libweston/compositor-drm.h
+++ b/libweston/compositor-drm.h
@@ -29,12 +29,13 @@
 #define WESTON_COMPOSITOR_DRM_H
 
 #include "compositor.h"
+#include "plugin-registry.h"
 
 #ifdef  __cplusplus
 extern "C" {
 #endif
 
-#define WESTON_DRM_BACKEND_CONFIG_VERSION 1
+#define WESTON_DRM_BACKEND_CONFIG_VERSION 2
 
 struct libinput_device;
 
@@ -51,8 +52,17 @@ enum weston_drm_backend_output_mode {
 	WESTON_DRM_BACKEND_OUTPUT_PREFERRED,
 };
 
-struct weston_drm_backend_output_config {
-	struct weston_backend_output_config base;
+#define WESTON_DRM_OUTPUT_API_NAME "weston_drm_output_api_v1"
+
+struct weston_drm_output_api {
+	/** The mode to be used by the output. Refer to the documentation
+	 *  of WESTON_DRM_BACKEND_OUTPUT_PREFERRED for details.
+	 *
+	 * Returns 0 on success, -1 on failure.
+	 */
+	int (*set_mode)(struct weston_output *output,
+			enum weston_drm_backend_output_mode mode,
+			const char *modeline);
 
 	/** The pixel format to be used by the output. Valid values are:
 	 * - NULL - The format set at backend creation time will be used;
@@ -60,15 +70,26 @@ struct weston_drm_backend_output_config {
 	 * - "rgb565"
 	 * - "xrgb2101010"
 	 */
-	char *gbm_format;
+	void (*set_gbm_format)(struct weston_output *output,
+			       const char *gbm_format);
+
 	/** The seat to be used by the output. Set to NULL to use the
-	 * default seat. */
-	char *seat;
-	/** The modeline to be used by the output. Refer to the documentation
-	 * of WESTON_DRM_BACKEND_OUTPUT_PREFERRED for details. */
-	char *modeline;
+	 *  default seat.
+	 */
+	void (*set_seat)(struct weston_output *output,
+			 const char *seat);
 };
 
+static inline const struct weston_drm_output_api *
+weston_drm_output_get_api(struct weston_compositor *compositor)
+{
+	const void *api;
+	api = weston_plugin_api_get(compositor, WESTON_DRM_OUTPUT_API_NAME,
+				    sizeof(struct weston_drm_output_api));
+
+	return (const struct weston_drm_output_api *)api;
+}
+
 /** The backend configuration struct.
  *
  * weston_drm_backend_config contains the configuration used by a DRM
@@ -109,17 +130,6 @@ struct weston_drm_backend_config {
 	 */
 	char *gbm_format;
 
-	/** Callback used to configure the outputs.
-	 *
-	 * This function will be called by the backend when a new DRM
-	 * output needs to be configured.
-	 */
-	enum weston_drm_backend_output_mode
-		(*configure_output)(struct weston_compositor *compositor,
-				    bool use_current_mode,
-				    const char *name,
-				    struct weston_drm_backend_output_config *output_config);
-
 	/** Callback used to configure input devices.
 	 *
 	 * This function will be called by the backend when a new input device