Check plane is compatible with CRTC

This allows us to rule out some potential solutions.

Closes: https://github.com/emersion/libhwc/issues/2

display.c

@@ -70,6 +70,7 @@ static void plane_destroy(struct hwc_plane *plane)
 struct hwc_display *hwc_display_create(int drm_fd)
 {
 	struct hwc_display *display;
+	drmModeRes *drm_res;
 	drmModePlaneRes *drm_plane_res;
 	uint32_t i;
 
@@ -86,6 +87,24 @@ struct hwc_display *hwc_display_create(int drm_fd)
 	hwc_list_init(&display->planes);
 	hwc_list_init(&display->outputs);
 
+	drm_res = drmModeGetResources(drm_fd);
+	if (drm_res == NULL) {
+		hwc_display_destroy(display);
+		return NULL;
+	}
+
+	display->crtcs = malloc(drm_res->count_crtcs * sizeof(uint32_t));
+	if (display->crtcs == NULL) {
+		drmModeFreeResources(drm_res);
+		hwc_display_destroy(display);
+		return NULL;
+	}
+	display->crtcs_len = drm_res->count_crtcs;
+	memcpy(display->crtcs, drm_res->crtcs,
+	       drm_res->count_crtcs * sizeof(uint32_t));
+
+	drmModeFreeResources(drm_res);
+
 	/* TODO: allow users to choose which layers to hand over */
 	drm_plane_res = drmModeGetPlaneResources(drm_fd);
 	if (drm_plane_res == NULL) {
@@ -112,6 +131,7 @@ void hwc_display_destroy(struct hwc_display *display)
 	hwc_list_for_each_safe(plane, tmp, &display->planes, link) {
 		plane_destroy(plane);
 	}
+	free(display->crtcs);
 	free(display);
 }
 
@@ -222,6 +242,9 @@ bool output_choose_layers(struct hwc_output *output, struct plane_alloc *alloc,
 	if (plane->layer != NULL) {
 		goto skip;
 	}
+	if ((plane->possible_crtcs & (1 << output->crtc_index)) == 0) {
+		goto skip;
+	}
 
 	hwc_list_for_each(layer, &output->layers, link) {
 		if (layer->plane != NULL) {

include/private.h

@@ -9,11 +9,15 @@ struct hwc_display {
 
 	struct hwc_list planes; /* hwc_plane.link */
 	struct hwc_list outputs; /* hwc_output.link */
+
+	uint32_t *crtcs;
+	size_t crtcs_len;
 };
 
 struct hwc_output {
 	struct hwc_display *display;
 	uint32_t crtc_id;
+	size_t crtc_index;
 	struct hwc_list link; /* hwc_display.outputs */
 
 	struct hwc_list layers; /* hwc_layer.link */

output.c

@@ -1,11 +1,25 @@
 #include <stdlib.h>
 #include <string.h>
+#include <sys/types.h>
 #include "private.h"
 
 struct hwc_output *hwc_output_create(struct hwc_display *display,
 				     uint32_t crtc_id)
 {
 	struct hwc_output *output;
+	ssize_t crtc_index;
+	size_t i;
+
+	crtc_index = -1;
+	for (i = 0; i < display->crtcs_len; i++) {
+		if (display->crtcs[i] == crtc_id) {
+			crtc_index = i;
+			break;
+		}
+	}
+	if (crtc_index < 0) {
+		return NULL;
+	}
 
 	output = calloc(1, sizeof(*output));
 	if (output == NULL) {
@@ -13,6 +27,7 @@ struct hwc_output *hwc_output_create(struct hwc_display *display,
 	}
 	output->display = display;
 	output->crtc_id = crtc_id;
+	output->crtc_index = crtc_index;
 	hwc_list_init(&output->layers);
 	hwc_list_insert(&display->outputs, &output->link);
 	return output;