drm/ast: Fail probing if DDC channel could not be initialized

Expect the hardware to provide a DDC channel. Fail probing if its
initialization fails. Failing to initialize the DDC indicates a
larger problem, so there's no point in continuing.

v4:
	* give a rational in the commit message
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-3-tzimmermann@suse.de

drivers/gpu/drm/ast/ast_drv.h

@@ -160,7 +160,6 @@ struct ast_i2c_chan {
 
 struct ast_vga_connector {
 	struct drm_connector base;
-	struct ast_i2c_chan *i2c;
 };
 
 static inline struct ast_vga_connector *
@@ -171,7 +170,6 @@ to_ast_vga_connector(struct drm_connector *connector)
 
 struct ast_sil164_connector {
 	struct drm_connector base;
-	struct ast_i2c_chan *i2c;
 };
 
 static inline struct ast_sil164_connector *

drivers/gpu/drm/ast/ast_i2c.c

@@ -117,7 +117,7 @@ struct ast_i2c_chan *ast_i2c_create(struct drm_device *dev)
 
 	i2c = kzalloc(sizeof(struct ast_i2c_chan), GFP_KERNEL);
 	if (!i2c)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	i2c->adapter.owner = THIS_MODULE;
 	i2c->adapter.dev.parent = dev->dev;
@@ -142,10 +142,11 @@ struct ast_i2c_chan *ast_i2c_create(struct drm_device *dev)
 
 	ret = drmm_add_action_or_reset(dev, ast_i2c_release, i2c);
 	if (ret)
-		return NULL;
+		return ERR_PTR(ret);
+
 	return i2c;
 
 out_kfree:
 	kfree(i2c);
-	return NULL;
+	return ERR_PTR(ret);
 }

drivers/gpu/drm/ast/ast_mode.c

@@ -1345,22 +1345,18 @@ static int ast_crtc_init(struct drm_device *dev)
 
 static int ast_vga_connector_helper_get_modes(struct drm_connector *connector)
 {
-	struct ast_vga_connector *ast_vga_connector = to_ast_vga_connector(connector);
 	struct drm_device *dev = connector->dev;
 	struct ast_device *ast = to_ast_device(dev);
 	struct edid *edid;
 	int count;
 
-	if (!ast_vga_connector->i2c)
-		goto err_drm_connector_update_edid_property;
-
 	/*
 	 * Protect access to I/O registers from concurrent modesetting
 	 * by acquiring the I/O-register lock.
 	 */
 	mutex_lock(&ast->modeset_lock);
 
-	edid = drm_get_edid(connector, &ast_vga_connector->i2c->adapter);
+	edid = drm_get_edid(connector, connector->ddc);
 	if (!edid)
 		goto err_mutex_unlock;
 
@@ -1373,7 +1369,6 @@ static int ast_vga_connector_helper_get_modes(struct drm_connector *connector)
 
 err_mutex_unlock:
 	mutex_unlock(&ast->modeset_lock);
-err_drm_connector_update_edid_property:
 	drm_connector_update_edid_property(connector, NULL);
 	return 0;
 }
@@ -1394,19 +1389,18 @@ static int ast_vga_connector_init(struct drm_device *dev,
 				  struct ast_vga_connector *ast_vga_connector)
 {
 	struct drm_connector *connector = &ast_vga_connector->base;
+	struct ast_i2c_chan *i2c;
 	int ret;
 
-	ast_vga_connector->i2c = ast_i2c_create(dev);
-	if (!ast_vga_connector->i2c)
-		drm_err(dev, "failed to add ddc bus for connector\n");
+	i2c = ast_i2c_create(dev);
+	if (IS_ERR(i2c)) {
+		ret = PTR_ERR(i2c);
+		drm_err(dev, "failed to add ddc bus for connector; ret=%d\n", ret);
+		return ret;
+	}
 
-	if (ast_vga_connector->i2c)
-		ret = drm_connector_init_with_ddc(dev, connector, &ast_vga_connector_funcs,
-						  DRM_MODE_CONNECTOR_VGA,
-						  &ast_vga_connector->i2c->adapter);
-	else
-		ret = drm_connector_init(dev, connector, &ast_vga_connector_funcs,
-					 DRM_MODE_CONNECTOR_VGA);
+	ret = drm_connector_init_with_ddc(dev, connector, &ast_vga_connector_funcs,
+					  DRM_MODE_CONNECTOR_VGA, &i2c->adapter);
 	if (ret)
 		return ret;
 
@@ -1451,22 +1445,18 @@ static int ast_vga_output_init(struct ast_device *ast)
 
 static int ast_sil164_connector_helper_get_modes(struct drm_connector *connector)
 {
-	struct ast_sil164_connector *ast_sil164_connector = to_ast_sil164_connector(connector);
 	struct drm_device *dev = connector->dev;
 	struct ast_device *ast = to_ast_device(dev);
 	struct edid *edid;
 	int count;
 
-	if (!ast_sil164_connector->i2c)
-		goto err_drm_connector_update_edid_property;
-
 	/*
 	 * Protect access to I/O registers from concurrent modesetting
 	 * by acquiring the I/O-register lock.
 	 */
 	mutex_lock(&ast->modeset_lock);
 
-	edid = drm_get_edid(connector, &ast_sil164_connector->i2c->adapter);
+	edid = drm_get_edid(connector, connector->ddc);
 	if (!edid)
 		goto err_mutex_unlock;
 
@@ -1479,7 +1469,6 @@ static int ast_sil164_connector_helper_get_modes(struct drm_connector *connector
 
 err_mutex_unlock:
 	mutex_unlock(&ast->modeset_lock);
-err_drm_connector_update_edid_property:
 	drm_connector_update_edid_property(connector, NULL);
 	return 0;
 }
@@ -1500,19 +1489,18 @@ static int ast_sil164_connector_init(struct drm_device *dev,
 				     struct ast_sil164_connector *ast_sil164_connector)
 {
 	struct drm_connector *connector = &ast_sil164_connector->base;
+	struct ast_i2c_chan *i2c;
 	int ret;
 
-	ast_sil164_connector->i2c = ast_i2c_create(dev);
-	if (!ast_sil164_connector->i2c)
-		drm_err(dev, "failed to add ddc bus for connector\n");
+	i2c = ast_i2c_create(dev);
+	if (IS_ERR(i2c)) {
+		ret = PTR_ERR(i2c);
+		drm_err(dev, "failed to add ddc bus for connector; ret=%d\n", ret);
+		return ret;
+	}
 
-	if (ast_sil164_connector->i2c)
-		ret = drm_connector_init_with_ddc(dev, connector, &ast_sil164_connector_funcs,
-						  DRM_MODE_CONNECTOR_DVII,
-						  &ast_sil164_connector->i2c->adapter);
-	else
-		ret = drm_connector_init(dev, connector, &ast_sil164_connector_funcs,
-					 DRM_MODE_CONNECTOR_DVII);
+	ret = drm_connector_init_with_ddc(dev, connector, &ast_sil164_connector_funcs,
+					  DRM_MODE_CONNECTOR_DVII, &i2c->adapter);
 	if (ret)
 		return ret;