compositor-drm: Support configuring the framebuffer format from weston.ini

This patch adds a new weston.ini key, gbm-format, to the [core] section.
This new key can be rgb565, xrgb8888 or xrgb2101010, and makes the
compositor use the corresponding GBM format for the framebuffer.

man/weston.ini.man

@@ -104,6 +104,13 @@ directory are:
 .BR xwayland.so
 .fi
 .RE
+.TP 7
+.BI "gbm-format="format
+sets the GBM format used for the framebuffer for the GBM backend. Can be
+.B xrgb8888,
+.B xrgb2101010,
+.B rgb565.
+By default, xrgb8888 is used.
 .RS
 .PP
 

src/compositor-drm.c

@@ -2581,9 +2581,11 @@ drm_compositor_create(struct wl_display *display,
 		      struct weston_config *config)
 {
 	struct drm_compositor *ec;
+	struct weston_config_section *section;
 	struct udev_device *drm_device;
 	struct wl_event_loop *loop;
 	const char *path;
+	char *s;
 	uint32_t key;
 
 	weston_log("initializing drm backend\n");
@@ -2595,7 +2597,23 @@ drm_compositor_create(struct wl_display *display,
 	/* KMS support for sprites is not complete yet, so disable the
 	 * functionality for now. */
 	ec->sprites_are_broken = 1;
-	ec->format = GBM_FORMAT_XRGB8888;
+
+	section = weston_config_get_section(config, "core", NULL, NULL);
+	weston_config_section_get_string(section,
+					 "gbm-format", &s, "xrgb8888");
+	if (strcmp(s, "xrgb8888") == 0)
+		ec->format = GBM_FORMAT_XRGB8888;
+	else if (strcmp(s, "rgb565") == 0)
+		ec->format = GBM_FORMAT_RGB565;
+	else if (strcmp(s, "xrgb2101010") == 0)
+		ec->format = GBM_FORMAT_XRGB2101010;
+	else {
+		weston_log("fatal: unrecognized pixel format: %s\n", s);
+		free(s);
+		goto err_base;
+	}
+	free(s);
+
 	ec->use_pixman = param->use_pixman;
 
 	if (weston_compositor_init(&ec->base, display, argc, argv,

weston.ini

@@ -1,6 +1,7 @@
 [core]
 #modules=xwayland.so,cms-colord.so
 #shell=desktop-shell.so
+#gbm-format=xrgb2101010
 
 [shell]
 background-image=/usr/share/backgrounds/gnome/Aqua.jpg