drm: introduce drm_writeback_connector_init_with_encoder() API

For vendors drivers which pass an already allocated and
initialized encoder especially for cases where the encoder
hardware is shared OR the writeback encoder shares the resources
with the rest of the display pipeline introduce a new API,
drm_writeback_connector_init_with_encoder() which expects
an initialized encoder as a parameter and only sets up the
writeback connector.

changes in v5:
- fix the encoder doc to indicate that its not valid for
users of drm_writeback_connector_init_with_encoder()

Reviewed-by: Liviu Dudau <[e-mail]>
Signed-off-by: Abhinav Kumar <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/483500/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/drm_writeback.c

···
 				 const u32 *formats, int n_formats,
 				 u32 possible_crtcs)
 {
+	int ret = 0;
+
+	drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
+
+	wb_connector->encoder.possible_crtcs = possible_crtcs;
+
+	ret = drm_encoder_init(dev, &wb_connector->encoder,
+			       &drm_writeback_encoder_funcs,
+			       DRM_MODE_ENCODER_VIRTUAL, NULL);
+	if (ret)
+		return ret;
+
+	ret = drm_writeback_connector_init_with_encoder(dev, wb_connector, &wb_connector->encoder,
+			con_funcs, formats, n_formats);
+
+	if (ret)
+		drm_encoder_cleanup(&wb_connector->encoder);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_writeback_connector_init);
+
+/**
+ * drm_writeback_connector_init_with_encoder - Initialize a writeback connector with
+ * a custom encoder
+ *
+ * @dev: DRM device
+ * @wb_connector: Writeback connector to initialize
+ * @enc: handle to the already initialized drm encoder
+ * @con_funcs: Connector funcs vtable
+ * @formats: Array of supported pixel formats for the writeback engine
+ * @n_formats: Length of the formats array
+ *
+ * This function creates the writeback-connector-specific properties if they
+ * have not been already created, initializes the connector as
+ * type DRM_MODE_CONNECTOR_WRITEBACK, and correctly initializes the property
+ * values.
+ *
+ * This function assumes that the drm_writeback_connector's encoder has already been
+ * created and initialized before invoking this function.
+ *
+ * In addition, this function also assumes that callers of this API will manage
+ * assigning the encoder helper functions, possible_crtcs and any other encoder
+ * specific operation.
+ *
+ * Drivers should always use this function instead of drm_connector_init() to
+ * set up writeback connectors if they want to manage themselves the lifetime of the
+ * associated encoder.
+ *
+ * Returns: 0 on success, or a negative error code
+ */
+int drm_writeback_connector_init_with_encoder(struct drm_device *dev,
+		struct drm_writeback_connector *wb_connector, struct drm_encoder *enc,
+		const struct drm_connector_funcs *con_funcs, const u32 *formats,
+		int n_formats)
+{
 	struct drm_property_blob *blob;
 	struct drm_connector *connector = &wb_connector->base;
 	struct drm_mode_config *config = &dev->mode_config;
···
 	if (IS_ERR(blob))
 		return PTR_ERR(blob);
 
-	drm_encoder_helper_add(&wb_connector->encoder, enc_helper_funcs);
-
-	wb_connector->encoder.possible_crtcs = possible_crtcs;
-
-	ret = drm_encoder_init(dev, &wb_connector->encoder,
-			       &drm_writeback_encoder_funcs,
-			       DRM_MODE_ENCODER_VIRTUAL, NULL);
-	if (ret)
-		goto fail;
 
 	connector->interlace_allowed = 0;
 
···
 	if (ret)
 		goto connector_fail;
 
-	ret = drm_connector_attach_encoder(connector,
-						&wb_connector->encoder);
+	ret = drm_connector_attach_encoder(connector, enc);
 	if (ret)
 		goto attach_fail;
 
···
 attach_fail:
 	drm_connector_cleanup(connector);
 connector_fail:
-	drm_encoder_cleanup(&wb_connector->encoder);
-fail:
 	drm_property_blob_put(blob);
 	return ret;
 }
-EXPORT_SYMBOL(drm_writeback_connector_init);
+EXPORT_SYMBOL(drm_writeback_connector_init_with_encoder);
 
 int drm_writeback_set_fb(struct drm_connector_state *conn_state,
 			 struct drm_framebuffer *fb)

include/drm/drm_writeback.h

···
 	 * @drm_writeback_connector control the behaviour of the @encoder
 	 * by passing the @enc_funcs parameter to drm_writeback_connector_init()
 	 * function.
+	 * For users of drm_writeback_connector_init_with_encoder(), this field
+	 * is not valid as the encoder is managed within their drivers.
 	 */
 	struct drm_encoder encoder;
 
···
 				 const struct drm_encoder_helper_funcs *enc_helper_funcs,
 				 const u32 *formats, int n_formats,
 				 u32 possible_crtcs);
+
+int drm_writeback_connector_init_with_encoder(struct drm_device *dev,
+				struct drm_writeback_connector *wb_connector,
+				struct drm_encoder *enc,
+				const struct drm_connector_funcs *con_funcs, const u32 *formats,
+				int n_formats);
 
 int drm_writeback_set_fb(struct drm_connector_state *conn_state,
 			 struct drm_framebuffer *fb);