drm/ast: Handle failed I2C initialization gracefully

I2C initialization is allowed to fail. In this case, create a connector
without DDC adapter. The current code would dereference a NULL pointer.

Reading the modes from the connector is supposed to work without I2C
adapter. Add the respective test.

v2:
	* init edid to NULL to avoid uninitialized read (Dan)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20211206091125.29501-2-tzimmermann@suse.de

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 1e30eaeb0e1b3a75d33eea41ad508d686284c4d1..692e7a3b35556dfe5f41cfa3fc21197ee8920948 100644 (file)
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -1210,9 +1210,9 @@ static int ast_get_modes(struct drm_connector *connector)
 {
        struct ast_connector *ast_connector = to_ast_connector(connector);
        struct ast_private *ast = to_ast_private(connector->dev);
-       struct edid *edid;
-       int ret;
+       struct edid *edid = NULL;
        bool flags = false;
+       int ret;
 
        if (ast->tx_chip_type == AST_TX_DP501) {
                ast->dp501_maxclk = 0xff;
@@ -1226,7 +1226,7 @@ static int ast_get_modes(struct drm_connector *connector)
                else
                        kfree(edid);
        }
-       if (!flags)
+       if (!flags && ast_connector->i2c)
                edid = drm_get_edid(connector, &ast_connector->i2c->adapter);
        if (edid) {
                drm_connector_update_edid_property(&ast_connector->base, edid);
@@ -1332,10 +1332,13 @@ static int ast_connector_init(struct drm_device *dev)
        if (!ast_connector->i2c)
                drm_err(dev, "failed to add ddc bus for connector\n");
 
-       drm_connector_init_with_ddc(dev, connector,
-                                   &ast_connector_funcs,
-                                   DRM_MODE_CONNECTOR_VGA,
-                                   &ast_connector->i2c->adapter);
+       if (ast_connector->i2c)
+               drm_connector_init_with_ddc(dev, connector, &ast_connector_funcs,
+                                           DRM_MODE_CONNECTOR_VGA,
+                                           &ast_connector->i2c->adapter);
+       else
+               drm_connector_init(dev, connector, &ast_connector_funcs,
+                                  DRM_MODE_CONNECTOR_VGA);
 
        drm_connector_helper_add(connector, &ast_connector_helper_funcs);