drm/ast: Add BMC virtual connector

Most aspeed devices have a BMC, which allows to remotely see the screen.
Also in the common use case, those servers don't have a display connected.
So add a Virtual connector, to reflect that even if no display is
connected, the framebuffer can still be seen remotely.
This prepares the work to implement a detect_ctx() for the Display port
connector.

v4: call drm_add_modes_noedid() with 4096x4096 (Thomas Zimmermann)
    remove useless struct field init to 0 (Thomas Zimmermann)
    don't use drm_simple_encoder_init() (Thomas Zimmermann)
    inline ast_bmc_connector_init() (Thomas Zimmermann)

Fixes: fae7d186 ("drm/probe-helper: Default to 640x480 if no EDID on DP")
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230713134316.332502-1-jfalempe@redhat.com

drivers/gpu/drm/ast/ast_drv.h

@@ -214,6 +214,10 @@ struct ast_device {
 			struct drm_encoder encoder;
 			struct drm_connector connector;
 		} astdp;
+		struct {
+			struct drm_encoder encoder;
+			struct drm_connector connector;
+		} bmc;
 	} output;
 
 	bool support_wide_screen;

drivers/gpu/drm/ast/ast_mode.c

@@ -1735,6 +1735,60 @@ static int ast_astdp_output_init(struct ast_device *ast)
 	return 0;
 }
 
+/*
+ * BMC virtual Connector
+ */
+
+static const struct drm_encoder_funcs ast_bmc_encoder_funcs = {
+	.destroy = drm_encoder_cleanup,
+};
+
+static int ast_bmc_connector_helper_get_modes(struct drm_connector *connector)
+{
+	return drm_add_modes_noedid(connector, 4096, 4096);
+}
+
+static const struct drm_connector_helper_funcs ast_bmc_connector_helper_funcs = {
+	.get_modes = ast_bmc_connector_helper_get_modes,
+};
+
+static const struct drm_connector_funcs ast_bmc_connector_funcs = {
+	.reset = drm_atomic_helper_connector_reset,
+	.fill_modes = drm_helper_probe_single_connector_modes,
+	.destroy = drm_connector_cleanup,
+	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
+};
+
+static int ast_bmc_output_init(struct ast_device *ast)
+{
+	struct drm_device *dev = &ast->base;
+	struct drm_crtc *crtc = &ast->crtc;
+	struct drm_encoder *encoder = &ast->output.bmc.encoder;
+	struct drm_connector *connector = &ast->output.bmc.connector;
+	int ret;
+
+	ret = drm_encoder_init(dev, encoder,
+			       &ast_bmc_encoder_funcs,
+			       DRM_MODE_ENCODER_VIRTUAL, "ast_bmc");
+	if (ret)
+		return ret;
+	encoder->possible_crtcs = drm_crtc_mask(crtc);
+
+	ret = drm_connector_init(dev, connector, &ast_bmc_connector_funcs,
+				 DRM_MODE_CONNECTOR_VIRTUAL);
+	if (ret)
+		return ret;
+
+	drm_connector_helper_add(connector, &ast_bmc_connector_helper_funcs);
+
+	ret = drm_connector_attach_encoder(connector, encoder);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
 /*
  * Mode config
  */
@@ -1842,6 +1896,9 @@ int ast_mode_config_init(struct ast_device *ast)
 		if (ret)
 			return ret;
 	}
+	ret = ast_bmc_output_init(ast);
+	if (ret)
+		return ret;
 
 	drm_mode_config_reset(dev);