Better handle outputs without CRTC

This happens if you plug in more outputs than supported by your GPU.

This patch makes it so outputs without CRTCs appear as disabled. As soon as
they get a CRTC (signalled via the mode event), we can enable them.

include/sway/config.h

@@ -568,7 +568,7 @@ struct output_config *new_output_config(const char *name);
 
 void merge_output_config(struct output_config *dst, struct output_config *src);
 
-void apply_output_config(struct output_config *oc, struct sway_output *output);
+bool apply_output_config(struct output_config *oc, struct sway_output *output);
 
 struct output_config *store_output_config(struct output_config *oc);
 

include/sway/output.h

@@ -31,7 +31,7 @@ struct sway_output {
 	int lx, ly;
 	int width, height;
 
-	bool enabled;
+	bool enabled, configured;
 	list_t *workspaces;
 
 	struct sway_output_state current;

sway/config/output.c

@@ -137,13 +137,12 @@ struct output_config *store_output_config(struct output_config *oc) {
 	return oc;
 }
 
-static void set_mode(struct wlr_output *output, int width, int height,
+static bool set_mode(struct wlr_output *output, int width, int height,
 		float refresh_rate) {
 	int mhz = (int)(refresh_rate * 1000);
 	if (wl_list_empty(&output->modes)) {
 		wlr_log(WLR_DEBUG, "Assigning custom mode to %s", output->name);
-		wlr_output_set_custom_mode(output, width, height, mhz);
-		return;
+		return wlr_output_set_custom_mode(output, width, height, mhz);
 	}
 
 	struct wlr_output_mode *mode, *best = NULL;
@@ -158,10 +157,12 @@ static void set_mode(struct wlr_output *output, int width, int height,
 	}
 	if (!best) {
 		wlr_log(WLR_ERROR, "Configured mode for %s not available", output->name);
+		wlr_log(WLR_INFO, "Picking default mode instead");
+		best = wl_container_of(output->modes.prev, mode, link);
 	} else {
 		wlr_log(WLR_DEBUG, "Assigning configured mode to %s", output->name);
-		wlr_output_set_mode(output, best);
 	}
+	return wlr_output_set_mode(output, best);
 }
 
 void terminate_swaybg(pid_t pid) {
@@ -174,33 +175,48 @@ void terminate_swaybg(pid_t pid) {
 	}
 }
 
-void apply_output_config(struct output_config *oc, struct sway_output *output) {
+bool apply_output_config(struct output_config *oc, struct sway_output *output) {
 	struct wlr_output *wlr_output = output->wlr_output;
 
-	if (oc && oc->enabled == 0) {
+	if (oc && !oc->enabled) {
+		// Output is configured to be disabled
 		if (output->enabled) {
 			output_disable(output);
 			wlr_output_layout_remove(root->output_layout, wlr_output);
 		}
 		wlr_output_enable(wlr_output, false);
-		return;
+		return true;
 	} else if (!output->enabled) {
+		// Output is not enabled. Enable it, output_enable will call us again.
 		if (!oc || oc->dpms_state != DPMS_OFF) {
 			wlr_output_enable(wlr_output, true);
 		}
 		output_enable(output, oc);
-		return;
+		return true;
 	}
 
+	bool modeset_success;
 	if (oc && oc->width > 0 && oc->height > 0) {
 		wlr_log(WLR_DEBUG, "Set %s mode to %dx%d (%f GHz)", oc->name, oc->width,
 			oc->height, oc->refresh_rate);
+		modeset_success =
 			set_mode(wlr_output, oc->width, oc->height, oc->refresh_rate);
 	} else if (!wl_list_empty(&wlr_output->modes)) {
 		struct wlr_output_mode *mode =
 			wl_container_of(wlr_output->modes.prev, mode, link);
-		wlr_output_set_mode(wlr_output, mode);
+		modeset_success = wlr_output_set_mode(wlr_output, mode);
+	} else {
+		// Output doesn't support modes
+		modeset_success = true;
 	}
+	if (!modeset_success) {
+		// Failed to modeset, maybe the output is missing a CRTC. Leave the
+		// output disabled for now and try again when the output gets the mode
+		// we asked for.
+		wlr_log(WLR_ERROR, "Failed to modeset output %s", wlr_output->name);
+		return false;
+	}
+
 	if (oc && oc->scale > 0) {
 		wlr_log(WLR_DEBUG, "Set %s scale to %f", oc->name, oc->scale);
 		wlr_output_set_scale(wlr_output, oc->scale);
@@ -264,6 +280,8 @@ void apply_output_config(struct output_config *oc, struct sway_output *output) {
 			break;
 		}
 	}
+
+	return true;
 }
 
 static void default_output_config(struct output_config *oc,

sway/desktop/output.c

@@ -503,7 +503,18 @@ static void handle_destroy(struct wl_listener *listener, void *data) {
 
 static void handle_mode(struct wl_listener *listener, void *data) {
 	struct sway_output *output = wl_container_of(listener, output, mode);
+	if (!output->configured) {
+		return;
+	}
 	if (!output->enabled) {
+		struct output_config *oc = output_find_config(output);
+		if (output->wlr_output->current_mode != NULL &&
+				(!oc || oc->enabled)) {
+			// We want to enable this output, but it didn't work last time,
+			// possibly because we hadn't enough CRTCs. Try again now that the
+			// output has a mode.
+			output_enable(output, oc);
+		}
 		return;
 	}
 	arrange_layers(output);
@@ -592,7 +603,6 @@ void handle_new_output(struct wl_listener *listener, void *data) {
 	output->damage_destroy.notify = damage_handle_destroy;
 
 	struct output_config *oc = output_find_config(output);
-
 	if (!oc || oc->enabled) {
 		output_enable(output, oc);
 	} else {

sway/tree/output.c

@@ -78,6 +78,12 @@ void output_enable(struct sway_output *output, struct output_config *oc) {
 	}
 
 	output->enabled = true;
+	if (!apply_output_config(oc, output)) {
+		output->enabled = false;
+		return;
+	}
+
+	output->configured = true;
 	list_add(root->outputs, output);
 
 	output->lx = wlr_output->lx;
@@ -104,8 +110,6 @@ void output_enable(struct sway_output *output, struct output_config *oc) {
 		ipc_event_workspace(NULL, ws, "init");
 	}
 
-	apply_output_config(oc, output);
-
 	if (ws && config->default_orientation == L_NONE) {
 		// Since the output transformation and resolution could have changed
 		// due to applying the output config, the previously set layout for the