drm/vkms: Add support for writeback module

Add enable_writeback feature to vkms_config as a module.
Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com>
Reviewed-by: Melissa Wen <melissa.srw@gmail.com>
Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/15802da4f1cdfed2b728c3d35731732f161dd073.1610391685.git.sylphrenadin@gmail.com

drivers/gpu/drm/vkms/vkms_drv.c

@@ -40,6 +40,10 @@ static bool enable_cursor = true;
 module_param_named(enable_cursor, enable_cursor, bool, 0444);
 MODULE_PARM_DESC(enable_cursor, "Enable/Disable cursor support");
 
+static bool enable_writeback = true;
+module_param_named(enable_writeback, enable_writeback, bool, 0444);
+MODULE_PARM_DESC(enable_writeback, "Enable/Disable writeback connector support");
+
 DEFINE_DRM_GEM_FOPS(vkms_driver_fops);
 
 static void vkms_release(struct drm_device *dev)
@@ -189,6 +193,7 @@ static int __init vkms_init(void)
 	default_config = config;
 
 	config->cursor = enable_cursor;
+	config->writeback = enable_writeback;
 
 	return vkms_create(config);
 }

drivers/gpu/drm/vkms/vkms_drv.h

@@ -83,6 +83,7 @@ struct vkms_output {
 struct vkms_device;
 
 struct vkms_config {
+	bool writeback;
 	bool cursor;
 	/* only set when instantiated */
 	struct vkms_device *dev;

drivers/gpu/drm/vkms/vkms_output.c

@@ -41,6 +41,7 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
 	struct drm_crtc *crtc = &output->crtc;
 	struct drm_plane *primary, *cursor = NULL;
 	int ret;
+	int writeback;
 
 	primary = vkms_plane_init(vkmsdev, DRM_PLANE_TYPE_PRIMARY, index);
 	if (IS_ERR(primary))
@@ -80,9 +81,11 @@ int vkms_output_init(struct vkms_device *vkmsdev, int index)
 		goto err_attach;
 	}
 
-	ret = vkms_enable_writeback_connector(vkmsdev);
-	if (ret)
-		DRM_ERROR("Failed to init writeback connector\n");
+	if (vkmsdev->config->writeback) {
+		writeback = vkms_enable_writeback_connector(vkmsdev);
+		if (writeback)
+			DRM_ERROR("Failed to init writeback connector\n");
+	}
 
 	drm_mode_config_reset(dev);